What is the Green Deal?

Posted in Green on April 23rd, 2014 by Andy
A cloudy green haze

Sometimes knowing what to do can seem like peering through a green fog…

The Green Deal is a government scheme to try and take some of the sting out of making green home improvements. The state of the housing stock in the UK is pretty dire, so we certainly need to do something, but is a Green Deal loan a good deal for homeowners? Well, yes and no…

How does it work?

Basically you as a homeowner make a booking with a Green Deal Assessor. This costs about £100-150, but you can sometimes get it for free. The Green Deal Assessor will have a bit of a look at your house, check your bills and make a bit of a rough estimate of the energy efficiency of your house. Based on this they’ll make some recommendations for improvements you could make that will pay for themselves in fuel savings. That last bit is important, it’s the “Golden Rule” of the Green Deal. You pay for the improvements by taking out a Green Deal loan, and the repayments on the loan aren’t supposed to cost you any more than you pay now, it’s all paid for through the efficiency improvements. The loan repayments are taken automatically out of your electricity bill.

The Green Deal can be used to fund anything from extra insulation to new boilers, solar panels, heat pumps, etc.

The assessor will also advise you of any Green Deal cashback grants that are available to you, it’s often worth getting an assessment done just to be eligible for these, even if you have no intention of taking out a loan.

Should I take out a Green Deal loan?

I reckon it’s like this:

You may notice that nowhere in this flow chart do I recommend getting an actual Green Deal loan. That’s for a couple of good reasons:

  1. The interest rates aren’t good. If you need to take out loan you can get a better deal from normal lenders like your bank or a building society. You’ll save money doing it this way.
  2. A Green Deal loan is tied to the property, so could make it difficult to sell your house. Buyers are understandably wary of taking on a debt incurred by someone else, even though the “Golden Rule” supposedly means they’d only be paying what they would have paid in the bills anyway.

So is the Green Deal pointless?


Green Deal assessments are useful, they help people decide what they should improve. Adding more insulation and draughtproofing is very cost-effective, and almost anyone will benefit from improving it but a lot of people don’t realise this. A Green Deal assessment should spell it out. The fact is you don’t need to spunk megabucks on green bling to save money and cut carbon.

Also, having an assessment done frees up Green Deal cashback funding you can use to subsidise improvements. Even if you have no intention of taking a Green Deal loan, it can be well worth your money to get an assessment done.


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Electricity Suppliers’ Fuel Mix 2013

Posted in Green on December 30th, 2013 by Andy
Wind turbines silhouetted against a sunset

How much of an effect do these things really have?

How clean is UK electricity really? How much cleaner is the supply from a “green” electricity company? Will switching to electric cars mean less pollution?

All these questions depend on the fuel mix of the electricity supply. The power plants operated by some power companies are much dirtier than others, and by law all companies are required to declare where they’re getting the juice they sell you. The list below is an updated version of the one I compiled last year.

SupplierNuclearGasCoalRenewOtherCO2 intensityCO2 emissionsCost on billExternal costCost including external
British Gas28%34%26%10%2%0.3791,251£521.21£59.32£580.53
Southern / Scottish Hydro / Swalec / Atlantic / M&S /Ebico1%28%54%15%2%0.6132,023£534.81£104.26£639.07
Scottish Power1%26%59%13%1%0.6402,112£531.99£111.27£643.26
Good Energy0%0%0%100%0%0.0000£533.72£1.82£535.54
Utility Warehouse0%51%34%14%1%0.5121,690£558.58£68.75£627.33
First Utility5%31%52%8%4%0.4701,551£581.42£106.03£687.45
Green Energy UK0%79%0%21%0%0.190627£498.96£10.55£509.51
Spark Energy5%31%52%8%4%0.6192,043£492.33£106.03£598.36


The supplier’s standard tariff was used, and does not take into account any discounts or special offers.

External costs are (in pence per kWh): coal = 5.4, gas = 0.39, nuclear = 0.48, renewable = 0.055, other = 6.05. (source: Pearce et al 1992). Fuel mix multiplied by this number gives the external cost, and the annual total shown above is for 3300kWh.

The Big Six

Between them Npower, British Gas, EDF, EON, SSE and Scottish Power supply 90% of homes in the UK, so the power they’re generating is the most important.

  • Npower: Once again, one of the worst suppliers. They manage to combine high prices with a supply that has actually got dirtier recently. Avoid.
  • British Gas: Rising prices and a somewhat less clean supply than last year has eaten into their lead over the other Big 6, but they’re still the best overall.
  • EDF: Snapping at BG’s heels comes EDF. They’re slightly more expensive but the carbon intensity of the power they feed into the gird has dropped even further, and they’re now the cleanest generator among the Big 6 by a long way. At 0.161kg CO2e kWh-1 they now supply genuinely low-carbon electricity to 5.7 million households. If you want a Big 6 supplier, you could do far worse.
  • EON: Their use of coal has leapt from 30% to 50% in the last year, and the numbers reflect it. Cheap, but definitely a generator that’s heading in the wrong direction.
  • SSE: The biggest supplier of renewable power to the grid is also one of the burners of coal, which erases all the good work on renewables.  Their coal use has also leapt this year, from 35% to 54%, which represents a huge amount of coal burned. Don’t buy your power from here if you like living on Earth.
  • Scottish Power: Saving the worst for last, Scottish Power claims the wooden spoon from Npower this year. Despite supplying good amounts of renewable power their heavy reliance on coal over gas makes them the dirtiest supplier on the grid.

Smaller suppliers

The big winner this year is Green Energy UK, who combine seriously low prices with the second cleanest fuel mix (base on natural gas an renewables). Only the 100% renewable Good Energy beat them on external cost, but can’t match their prices. Other honourable mentions go to LOCO2 and Ecotricity, both of which manage to beat all of the Big 6 on price and green credentials.

Less impressive are Spark Energy, who are cheap but very dirty, and First Utility who once again claim the dubious honour of being the worst supplier in Britain. If I was one of their customers I would really want to know why they seem to pay so much for the dirtiest power available, when it should be the cheapest.

Ovo’s performance looks pretty lacklustre, but like Ecotricity and Green Energy Uk they also have a 100% green tariff that would be well worth a look.

What is the “external cost”?

It’s an attempt to sum up all the different negative impacts that generating energy has, from carbon emissions and deaths from poor air quality, to destruction of forests due to acid rain. It expresses this impact as a cost in pence per kWh generated. In a fair world, the source of that damage (ie: the owner of the power plant and their customers) would pay for that damage, so by adding the external cost to the actual cost of  your power you can get an idea of whether cheap dirty power is a better deal for society than expensive clean power.

If you’re feeling really keen to offset this you could of course make a donation to a green project equal to your external cost.  Or you could sink it into a green crowdfunding project like the ones on Abundance Generation. Just a thought.

Pearce, D.W., Bann, C. and Georgiou, S. (1992) The Social Costs of Fuel Cycles, Report to 
the UK Department of Energy,
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How to control indoor air quality

Posted in Green, Howto on May 25th, 2013 by Andy

I recently blogged about how I solved an indoor air quality problem in my house by fitting a single room MVHR unit, but thought it might be useful to look into the different ways to tackle this common problem.

A family seated at the dinner table wearing gas masks

There must be a better way

What causes mould, condensation and humidity indoors?

The amount of moisture that the air can hold varies with temperature. Warm air can hold more water than cold air. This is known as the Relative Humidity. An RH of 80% means that the air contains 80% of the maximum for that temperature. Cooling the air would cause the RH to go up, until at 100% the air could no longer contain that water, and it would condense out. So we need to avoid very moist air from touching anything cold and causing condensation.

The main sources of moisture in your home are wet rooms (ie: showers), cooking, and the presence of people. These all release moisture which if not ventilated can build up. Besides humidity the other problems for indoor air quality include CO2, volatile gases, radon, outside pollutants, etc. However monitoring humidity is cheap and easy, so can serve as a useful proxy for indoor air quality in general.

How can we tackle a dampness problem?

The first thing to do is buy a cheap humidity monitor and see what your RH is. It’s very difficult to tell without one, as people are pretty insensitive to humidity. If you’re seeing above about 70% RH in winter, you should take some action.

Eliminate sources of moisture


This means doing simple things like putting lids on pots on the stove, or opening the windows while showering (assuming it’s warm enough!).

  • Pros: Simple, costs nothing
  • Cons: Limited effectiveness, especially in winter.

Mechanical Extract Ventilation (MEV)

This includes simple extractor fans in wet places like the bathroom or kitchen. These vary widely in price, with the more effective humidistat controlled versions costing several times that of the cheapest. The range of fitting options are wide, you can fit them through walls or windows or you can mount them in the ceiling and run a duct through your loft to the eaves.

The main drawback is that by simply chucking all your nice warm internal air out they create negative pressure which sucks cold outside air  in elsewhere. So while your indoor air quality will improve, your house will be colder. At current energy prices it is still cheaper to burn more fuel to replace the lost heat than it is to pay for a more expensive MVHR option (see below), but there is the comfort and carbon footprint angle to consider. Most extractor fans are also very draughty when not running, although ones with shutters are available.

  • Pros: Wide range available, can be very cheap.
  • Cons: Substantial heat loss

Positive Input Ventilation (PIV)


Essentially the opposite of MEV, PIV continually forces fresh air into the house, creating a slight positive pressure within. That air needs to have a defined exit path, so you’ll need continually open airbricks, trickle vents or MEV as well.

PIV units are often mounted in the loft where they draw air that is not quite as cold as external air, but if you’ve insulated your loft as well as you should have the difference will be pretty minimal. Effectively the have the same drawback as MEV. Since they run continuously the temperature swings will be less uncomfortable, but overall your heating bills will be higher. Some are available with heating elements to warm incoming air, but since this is straight resistive heating it’s a very expensive and dirty way to heat your home.

  • Pros: Effective, and don’t cause sudden temperature drops.
  • Cons: Same heat loss as MEV, or very expensive if pre-heating the air supply.



Dehumidifiers can get the moisture out of the air without venting it to the outside, and have the bonus that the dried air releases some heat, and is easier to heat than moist air. This would seem like a good option for a green home, if not for one major risk.

Excess humidity means that the home is not well ventilated enough. Besides moisture other pollutants such as CO2 can build up. While a dehumidifier can remove the moisture it doesn’t remove anything else, and excessive CO2 levels indoors can cause fatigue, headaches, etc. I would advise people to use dehumidifiers sparingly, and only to deal with point sources of humidity such as drying clothes indoors. Don’t leave them running continuously unless you are also monitoring CO2 levels. Unfortunately CO2 monitors can be quite expensive.

The better solution IMO is to ventilate, not dehumidify.

  • Pros: Tackles the problem directly
  • Cons: Not particularly cheap, risks masking air quality problems.

Insulate cold spots


Condensation will only form when air is allowed to cool so much that the water condenses. By eliminating cold spots you prevent this dampness from forming. Old windows and doors can be replaced or secondary glazing fitted, air leaks can be plugged, and cold spots on walls can be insulated (watch out for voids in cavity insulation, or bits that people forget to insulate like dormer windows and the ceiling of bay windows).

  • Pros: Often an easy DIY job, reduces fuel bills.
  • Cons: Not always easy to do, cures condensation but doesn’t actually improve air quality.

Whole house MVHR (Mechanical Ventilation with Heat Recovery)


This is the gold-standard solution. Air is extracted through ducts, passed over a heat exchanger and vented. Fresh air is drawn in and picks up heat from the heat exchanger to supply warmed air.

Generally it is impractical to retrofit a whole-house MVHR unless you’re doing a major refurb, due to the need to run ducts. MVHR also requires a high standard of air tightness in the house, which has to be designed into the structure of the building. MVHR is popular in high-tech Passivhaus eco-homes, but is very rare otherwise due to the four-figure pricetag.

  • Pros: Effective, quiet, comfortable, green.
  • Cons: Expensive, requires highly air tight house, requires duct runs.

Single room MVHR


This is a hybrid of conventional MEV and MVHR. A continuously running fan is fitted through the wall of wet rooms such as the kitchen and bathroom, and includes a heat exchanger to warm the supply air. Often an old bathroom extractor fan can be directly replaced with a single room MVHR, making them ideal for retrofit.

In my case I’ve found a single MVHR in the bathroom has been sufficient to control humidity for my whole house.

  • Pros: Effective, retrofittable, reduces heat loss.
  • Cons: More expensive than MEV while doing basically the same job.
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Vent-Axia HR25H Single Room MVHR Review

Posted in Gadgets, Green, Tech on December 1st, 2012 by Andy

I’ve spent a bit of effort draughtproofing my house, which has been great for keeping the place warm. The downside is that a certain level of ventilation is necessary to prevent humidity building up. This means condensation, mould and other nastiness. This winter has been quite bad, with black mould growing on cold spots around the place. That’s unacceptable to me with wee kids in the house, so something needed to be done.

The problem has two solutions:

  1. Get the humidity down by increasing ventilation
  2. Eliminate cold spots where humid air would condense

The main sources of damp in a house will be the bathroom and kitchen. Using a cheap humidity monitor I’ve been tracking our humidity levels and found them consistently above the 70% danger level where problems arise. Clearly we needed to avoid pumping any more moisture into the house, so extract ventilation in the bathroom seems like the top priority.

I’ll be tackling the cold spots in due course too, but for now it’s time for some mechanical ventilation with heat recovery (MVHR).

What is MVHR?

I’m allergic to the idea of simply blowing air we’ve heated with fossil fuels straight out the side of the house, so instead of an extractor fan I went shopping for a through-wall mechanical ventilation heat recovery unit. Unlike a regular extractor fan these also draw in fresh air and pass it over a heat exchanger that recovers some of the heat from the outgoing air. As well as reducing draughts by supplying air to replace that extracted, it will reduce the cooling effect of sucking out the warm moist air.

Is it worth fitting MVHR?

New tightly sealed houses use whole-house MVHR systems, but these are a different kettle of fish. Indeed, fitting one is only worth it if your air tightness is very good. Given that I had a humidity problem I took my air tightness to be somewhat higher than it should be, and coupled to the carbon-saving and comfort boosting properties it seemed the extra expense was worth it.

The Vent-Axia HR25H

I chose the HR25H over several competing products (Envirovent Retrovent and it’s replacement the cringingly-named Heat Sava, Vent-Axia HR25 Solo and Tempra) due to the combination of good performance, low price, and generally positive reviews from owners. The unit is not balanced, it extracts slightly more than it inputs, but this is a plus point in my books as it will draw air from the rest of the house into the bathroom so that other rooms get the benefit too.

Essentially the HR25H is a plastic tube with a divider down the middle. This penetrates the wall, and the fans are mounted on the exterior end, with the filter and electronics on the inner end. A cartridge type plastic heat exchanger sits in the middle of the tube and the whole lot is powered by a switched-mode power supply unit located up to 5m away. Like all MVHR it’s designed to run constantly on trickle and speed up when needed. Like most people I opted for the humidistat controlled version so that it would automatically boost whenever it was needed. Sensitivity is controllable, although getting it right can take a bit of fiddling.


A view inside the existing hole in my wall

Just a smidge of drilling required to make this usable…

To install this MVHR you’ll need a 100mm or 152mm hole through your wall. I already had a large airbrick through the wall, which had been bodged about with during the time of previous owners and currently had a nasty plastic grille. This was a good thing, as core drilling all the way through 300mm of wall is not my idea of fun.

I had hoped to avoid drilling altogether, and simply bash enough of the airbrick out, but the vent narrowed inside the wall too much (difficult to see in the pics). You can hire core drilling kits for around £50, or hire someone else to do it for about £40-90.

It’s important to make sure you drill with a slight downwards slant (which is why the hole isn’t going through the top of the vent in the picture). Sitting a spirit level on the chuck of your drill and tilting until the bubble moves is good enough. This will ensure that any condensation that forms inside the heat exchanger drains outwards. This is important, you will get condensation inside it, and if it can’t escape it will fill up the heat exchanger and the unit will conk out.

The MVHR fitted into the wall and wiring going in

Note the tile-over-tile job from previous owners. I constantly find nasty things like this whenever I do any DIY on this house. Luckily they left some spare tiles for me so I can patch up the hideousness when I’m done.

I fitted a plastic wall sleeve to the hole and filled the rest of the void with expanding foam. I’m sure the latter is awful for the environment, but it’s supremely useful stuff for sealing weird shaped holes and penetrating little gaps. Then it’s simply a matter of sliding the HR25H into the sleeve where it seals very tightly due to the rubber seals around it. The kit includes 5m of cable to run to the power supply unit. I went straight up through the ceiling, across the top of the insulation in the roof and down to the wall outside the bathroom where an existing junction box was close. After wiring the MVHR to the low voltage side of the power supply box and having the mains connected to the high voltage side I hit the switch and it all powered up nicely. The power supply even includes a fuse and a switch, so there’s no requirement for any additional hardware to spur off your existing wiring.


The unit is quiet in trickle mode. You can hear it nearby, but only if you listen for it. After all my hard work I needed a shower and was pleased when boost came on almost immediately.

Boost mode is much noisier, but so is any extractor fan. If I listen up the stairs I can hear it running in the bathroom if the door is open. If you shut the bathroom door it’s barely audible in the bedrooms adjacent to the bathroom, so I won’t be waking anybody up when I’ve got an early start.

Some action snaps:

Time shows 13:27, humidity 70%

Immediately pre-shower. Temperature is reading a little high as I inadvertently left the monitor over a radiator for a few minutes just prior. So much for a controlled experiment…

Time 1332, humidity 87%

Immediately post-shower…

Time 1336, humidity 91%

Peak humidity. The monitor does lag a bit, I assume it’s averaging readings from the last few minutes.

Time 1400, humidity 84%

Seems to be working…

Time 1419, humidity 79%

…yep, definitely working!

Note the drop in temperature. Some of this is due to the accidentally high reading pre-shower, then the effect of running the hot shower, but some drop while ventilating is inevitable. External temperature was pretty chilly, probably no more than 10ºC. No heat exchanger is 100% efficient, and just think how much colder it would have got if we weren’t recovering some of the exhaust heat.

The humidistat is adjustable between 60-90% relative humidity. While the adjustment is just a case of twiddling a knob, you do have to remove the face of the MVHR to do this, which means it’s a screwdriver job. To be honest this is a pain , but once you get it right there should be no need to tinker. I found the best way was to set mine to be relatively insensitive so that it shut off too early. Then I tweaked it downwards until it went into boost again, and kept repeating this until I was happy with the RH level when it shut off.

Power usage is 2W in trickle and 22W in boost. I estimate mine will run in boost for about 2h a day, putting annual consumption at  under 16kWh (assuming it’s switched off for half the year). That’s around £2.25 for me, so worth every penny to prevent nasty mould spores getting at my kids.


Besides a regular clean of the filters little is required. Replacement heat exchangers are available and simple to fit. Some users have reported prematurely dead fans, but they have a five-year warranty on them, so it should only be nuisance value if they do conk out. The electronics are all easily accessible, and you can pull the whole unit out from inside, so there shouldn’t ever be any need to go up a ladder to attend to the outside.


I’m happy with the HR25H. At around £275 delivered it’s substantially cheaper than some of the competition, and performs well. My humidity readings are now in the low 60’s or high 50’s (max has been 67%), and it’s done so without wasting heat. Fitting it was pretty easy, especially since I could use an existing airbrick. Besides an occasional clean out it should do it’s thing without any effort from us, which is just how I like it.

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Windy 3HP Air Source Heat Pump Review

Posted in Green, Tech on November 8th, 2012 by Andy

A beige box with vents on the top and frontThe Fimer Windy 3HP (“hp” = heat pump) is a through-wall reversible air-conditioner which can function as a heat pump in winter and an air conditioner in summer (the two are essentially the same process run in reverse, just imaging you’re trying to cool the Earth’s atmosphere in winter and venting the waste heat into your house).

It’s a single unit that mounts on an internal wall getting it’s supply and vent through a single hole in the wall. Because of this there are no bulky units to fit outside your house, and the whole thing can be installed as a DIY job. It’s just about the easiest and cheapest way to get an air source heat pump into your home.

I recently fitted one to replace a segment of my gas boiler’s central heating that had never worked since we moved in, and as an experiment in heat pump heating this winter.

Big box goes on wall

The unit itself is a fat box about the size and shape of a large suitcase. It mounts onto a plate screwed to the wall and comes with a standard 3-pin plug, although I’ll be wiring mine into a fused spur once I’ve finished monitoring it via a plug-in meter. You’ll need to get out the core drill and punch a 150mm hole through your wall. From there two concentric plastic sleeves carry air in or out and the box simply hangs on the plate on the inner wall. It weighs 23kg, so it can be fitted single-handed if you’re careful. I’d get a friend in if you’re hefting your chunky heat pump above about knee height.

Internal air is drawn in the top through removable washable filters and vents horizontally out the front. This can create a bit of a breeze at full blast, so have a think about what you’re pointing it at. That’s not necessarily a bad thing though, my wee girl loves standing in front of it and having the warm air blow in her hair!

There are more powerful 4Hp and 5HP units available. They’re the same physical size, but are rated higher.

Good points

It heats pretty effectively, drawing up to about 700W maximum, and heats our small 3.5x4m room quickly. Stated COP is 3.14 in heating mode (at 7ºC outside, 21ºC inside), and max thermal output around 2.2kW. Since the air is blown out it doesn’t feel dangerously hot like a 2.2kW convection heater would, and the mixing of the air heats the room evenly and quickly. Compared to the floor-standing 3kW heater we were using air source heat pump is a massive upgrade, safer around the kids, and much cheaper to run.

Under control of its thermostat the unit seems quite accurate, coming up to the temperature set point without overshooting, and keeping the temperature nicely within about 0.5ºC.

A brick wall with a vent in it

The vent is pretty low-profile and unobtrusive (dodgy amateur concrete job notwithstanding…)

The vent on the outside wall is quite small and tidy, although not everyone will be a fan of the plasticky grille.

The wall unit contains no buttons, which is good for child-friendliness if mounted low down, but does leave you somewhat reliant on the tacky wee IR remote. Apparently an RF version exists too.

Power consumption on standby is good, at about 3W. This is low enough that measures like timer switches become pretty marginal, so it can just be left on standby if switching it off is inconvenient.

The unit itself is quite modestly styled and should suit a range of decor. It’s paintable if you want it to blend in further.

Not so good

Due to having the whole gubbins (compressor, fans, etc) inside one box it can be noisy. It’s about comparable to a powerful fan heater, and mine does have a slight whistle which is a little annoying, but not teeth-grindingly so.

The main problem is the controls, specifically the ability to automate. There is no proper facility for timed on/off cycles. The only facility it has is a delayed on or off function. In “Timer On” mode you set the machine up how you want and switch it off, leaving the remote pointed at it. At the right time the remote sends the “on” signal and off it goes. Likewise for “Timer Off”, set it running, leave the remote in view and it switches it off at the appointed time. Unfortunately you can’t set both on and off times, it’s one or the other. So every night I have to set mine to come on the next morning, then it has to be switched off manually. A bit poor really, Fimer really need to sort this out.

The remote must be left pointing at the unit for timer mode to work, I get around this limitation by putting some sticky velcro on the remote and leaving it stuck inside an alcove opposite. Again, you’ll need to think about where you’re positioning it to get around this (or try to find an RF version).

Power consumption when not heating or cooling is not great. When switched on the fans run constantly even if there’s no demand for heat (or cooling), drawing about 30W continuous. Nice for a bit of air movement, but it would be better if the fans stopped after a reasonable time of inactivity.

Due to the entire condenser being mounted indoors it will collect condensate in its internal tank even in heating mode, you’ll either need to empty this occasionally or fit the included auto drain kit. I  recommend the latter, it includes about a meter of rubber tubing, so have a think about where you’ll drain condensate to. Even if you don’t fit the full drain kit, fitting the tap from it makes draining the tank a lot easier, or else you’ll be needing an allen key to remove a fiddly drain plug every few days.

Dehumidify mode seems  fairly ineffective, I didn’t see anywhere near the stated 1l h-1 figure and it draws about 500W continuously. I’d recommend a proper demidifier with a decent sized tank if you need to control damp.

The box sticks out a fair way from the wall (about 300mm), so it won’t suit hallways.

Green credentials

The COP the manufacturer claims is 3.14 in heating mode. This means the best case scenario is that it will use 1kWh of electricity to create 3.14kWh of heat. Realistically you should probably expect more like 2.5 IMO, but maybe I’m being cynical. Whether this is greener than a gas boiler for example will depend on the CO2 intensity of your electricity supply.

My old gas boiler is 78% efficient, meaning that to create 100kWh of heat it will use 128kWh of gas, releasing 23.5kg of CO2.

The Windy 3HP will use something like 40kWh of electricity to do the same (assuming COP=2.5). At bog-standard grid carbon intensity that would release about 21kg CO2e, although taken as an annual aggregate your supplier may be better or worse than that (UK fuel mix: energy companies emissions compared). So marginally cleaner in carbon terms, but using electricity does allow you to get the supply from a clean source. For example, on a couple of mornings I’ve had enough sunshine to run the heat pump off my modest little 2kWp PV system at least some of the time, even in November. During spring and early autumn I’d expect to be doing this quite a lot. I hope the polar bears appreciate it.

Obviously if you’ve got a very clean gas boiler and a dirty electricity supply (Scottish Power is the worst by the way) then it might not make sense, but if you’re heating with oil or resistive heaters or have clean electricity available then you’ll be streaks ahead.

The refrigerant is a non-ozone depleting one (R410) as required by law. It’s still a pretty horrendous greenhouse gas so make sure it’s disposed of properly at end of life, or you’ll probably negate all the carbon savings it’s ever made.


Not a machine without flaws, but at about £400 delivered it’s got to be the most affordable air source heat pump available. It’s easy and cheap to fit, effective and will make your home a happier place. If you’re looking for an all-singing all-dancing air source heat pump to heat your whole home, this isn’t it. But if you’re using electric heating or want to take some load off your fossil-fuel spewing gas boiler then it’ll do the business.

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UK fuel mix: how clean is your electricity?

Posted in Green on October 21st, 2012 by Andy

The power that comes out of your wall from the national grid comes from a variety of sources: smoke belching coal plants, clean hydroelectric dams, or controversial nuclear reactors.

A smokestack belching smoke

Want to see less of this?

Different energy companies use a different fuel mix, and as a result the electricity the national grid supplies us differs in how green it is. If we want to be green,where should we get our power from?

Fuel Mix

By law, all UK energy companies have to publish their “fuel mix”. This is the proportion of their power that they get from various sources. From this we can put some actual numbers on how clean the different companies are:

SupplierNuclearGasCoalRenew.OtherCO2 Intensity
CO2 emissions
Cost on bill
External cost
Cost including external
Npower2%55%29%12%2%0.4741565£516.71£63.28£ 579.99
Brit Gas27%50%14%8%2%0.3161042£448.08£38.78£ 486.86
EDF / Sainsbuys69%0%28%3%0%0.253834£488.27£60.60£ 548.87
Eon6%49%30%11%4%0.4761570£499.56£69.23£ 568.79
Southern / Scottish Hydro / Swalec / Atlantic / M&S /Ebico1%49%35%14%1%0.5011653£485.42£71.09£ 556.51
Scottish Power0%40%47%14%0%0.5681874£483.23£88.80£ 572.03
Ecotricity*2%20%12%64%2%0.191630£488.31£28.82£ 517.13
Good Energy0%0%0%100%0%00£485.20£1.82£ 487.02
LoCO20%55%0%45%0%0.198653£ 452.31£7.90£ 460.21
Utility Warehouse2%55%29%12%2%0.4741565£ 436.02£63.28£ 499.30
First Utility6%52%32%5%4%0.5001651£ 564.50£73.76£ 638.26
Ovo*5%39%24%29%3%0.3771244£ 403.79£56.01£ 459.80
Green Energy UK*0%64%0%36%0%0.230760£ 460.44£8.89£ 469.33

*These suppliers also offer a fully green tariff that has the same 100% renewable fuel mix as Good Energy.

This table assumes the average UK domestic electricity consumption of 3300kWh per year. Prices shown are valid for October 2012 or the price rises due in Nov 2012 where applicable. Tariffs compared were the standard online dual fuel rate and do not include any special deals for new customers.

What is the “external cost”?

It’s a way of putting a number on all the damage done by emissions. It includes global warming potential, other environmental damage (such as acid rain), and health problems and deaths from air and water quality. The worst offenders are dirty fossil fuel power stations like coal and oil, but even renewable sources aren’t zero impact (they’re just very low).

When expressed as a monetary value, it represents the amount you’d have to pay extra to offset the actual damage from the emissions. Simply put, the lower the external cost, the cleaner and more sustainable the source. This is a more broad-ranging metric than simple CO2e emissions, which only evaluate global warming potential and none of the other negative impacts.

The actual numbers used (in pence per kWh): coal = 5.4, gas = 0.39, nuclear = 0.48, renewable = 0.055, other = 6.05. (source: Pearce et al 1992). Fuel mix multiplied by this number gives the external cost, and the annual total shown above is for 3300kWh.

But isn’t all power from the national grid the same?

No. While it’s true that even if you’re on a 100% renewables deal the actual electrons that reach you may have come from another source, the fact of an electricity supply contract is that it’s a two-way transaction. Electrons flow to you from the grid, and money flows away from you to your supplier. It doesn’t matter if the electrons you actually consume come from a coal plant at the end of your road, if the money you pay your power company obligates them to purchase the same amount of green energy and feed it into the national grid (possibly at a different time from when you are consuming electricity). The net result is that your consumption has caused the same amount of that type of electricity to be generated and fed into the grid. So there really are “green electrons” and “dirty electrons”, it’s just that the process is abstracted a little by the presence of the national grid.

What stands out?

Even within the Big 6 energy companies (not known for their greenness) there’s a wide variation in the quality of the supply. When you look at just CO2, EDF and British Gas are surprisingly good, getting almost as low as some of the smaller specialist green suppliers. However, EDF only gets so low because of all their nuclear plants, and this shows in the overall impact where they fall back into the pack of dirty offenders. In the long run, the green suppliers like Good Energy, LoCO2, Green Energy UK and Ecotricity all come out well ahead, although British Gas is actually not far off them (and is cheap!).

Npower is the worst of the big six, being both dirty and expensive. But if you want the absolute worst deal in Britain you’ll be heading off to First Utility.

Scotland is a country keen to promote it’s renewable resources but unfortunately the Scottish companies seem to be topping up their decent renewable percentages with a lot of coal, so end up being some of the dirtiest. Oops.

Ovo are the cheapest overall, but LoCO2 only cost £1 more a year and emit about half as much CO2. If you go with Ovo, use their proper green tariff, as their standard one is pretty dirty.


If you want the cleanest electricity available you can’t beat Good Energy, LoCO2, or the green tariffs from Ecotricity, Ovo and Green Energy UK. If you want to go with a major supplier, British Gas is by far the cleanest electricity.

Disclosure: I’m a Good Energy customer, and wholeheartedly recommend them. If you’d like to switch to them and get a £25 bonus for us both, please get in touch.

Pearce, D.W., Bann, C. and Georgiou, S. (1992) The Social Costs of Fuel Cycles, Report to 
the UK Department of Energy,
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Insulation and refurb for the kids bedroom

Posted in Green, Tech on August 13th, 2012 by Andy

We’ve got our second child on the way, so it’s time to shift the nursery from the box room to something bigger, and the room could do with some more insulation. We’ve been using it as a study (and to be honest a bit of a dumping zone) but it’s a good size and will be much better used as the kids’ bedroom. The project would also be a nice little experiment for me in internal wall insulation.

A cold-looking baby bundled up with just the face showing

Grumpy cold babies: what we’re all trying to avoid…

The Problem

This room is cold and ugly. It has nasty old metal-framed single glazed windows and a giant hole in the wall (air brick). There was a hideous mauve wallpaper peeling from the walls. Something had to be done.

The Solution

  • Re-line the external wall with internal wall insulation.
  • Seal the air vent.
  • Strip wallpaper and paint a neutral colour. We’ll be applying stickers that the kids can change as they grow or we move things around.
  • New double-glazing

I opted for Kingspan K17 insulated plasterboard for the internal wall insulation. I like the way everything is integrated into one slab. It gets stuck straight onto the walls with adhesive and has a vapour control layer to prevent condensation inside the wall (a genuine problem when adding insulation). Thermal conductivity is 0.021W mK-1.

Getting it done

Luckily the old wallpaper was in such poor condition that most of it came away by hand. We’ve got an el cheaper wallpaper stripper from B&Q and used that on the stubborn bits. Underneath we found an unpleasant green paint/primer/something that we’ve struck elsewhere in the house. It’s nasty flaky rubbish that turns to mush when steamed, and alternately sticks like shit to a blanket or falls off the wall at the drop of a hat. We gambled and didn’t remove it all, just a bit of a sand on the loose bits, and most of it seems alright. If all the paint falls off in a year’s time I guess we’ll know we ballsed that up.

A slab of insulated plasterboard

Insulated plasterboard has the high-performance insulation bonded to the back of the plasterboard, with a foil vapour control layer in between.

I stuck the Kingspan K17 to the outside wall using Insta Stik MP. Very easy to use, but if you’re using the “self applicator” type with a little plastic tube instead of a gun be aware that you can’t stop half way through as it keeps seeping out of the nozzle, so cut all your boards and check them for fit before you start gumming them to the wall. I used a continuous bead of the stuff around the edges to try to prevent vapour getting behind the insulation slabs from the joints.

Doing  the actual insulation slabs was easy, but I underestimated the amount of work that changing skirting boards, coving, radiators, and fitting new window boards would create. I was limited to quite a thin type of Kingspan K17 by the piping for the radiator, so could only fit 25mm (plus plasterboard makes 37.5mm). Make sure you plan your cuts around the windows carefully, so that you can use the parts you’re removing to do inside the window reveals (otherwise they’ll act as cold bridges). You don’t want to have to buy extra sheets just to do details.

The cavity in the wall for the air brick was stuffed with offcuts of rockwool and I simply stuck the Kingpsan K17 over the top. Should be well insulated and air tight.

For paint we went for some Dulux one coat. I’d not used one coat paint before and was skeptical, but it covered really well. A couple of spots needed a quick second coat after half and hour, but otherwise it covered really well.

Moving the wall inwards meant shortening the skirting boards on the adjacent walls, and new coving as the old stuff doesn’t survive being pulled off. The change in depth of the window reveals also means the old window sills were too short, so new PVC window boards went on.


The nasty old metal Crittal windows might as well have been a hole in the wall, so out they went and in their place came in some nice new double glazed units supplied by Unique Windows Doors and Conservatories, a local company. I highly recommend this father and son team if you’re in the southeast of England. Very good standard of parts and workmanship, nice blokes and a good price to boot.

Frames were from Liniar, glazing units were some 4-16-4 Argon filled Pilkington K.

Thermal performance

The wall was composed of three heat-losing elements:

  • Brick wall with cavity wall insulation inside it
  • Single glazed metal-framed windows
  • Air vent
Before After Max heat loss before Max heat loss after Annual heat saving Annual cost saving Annual CO2 saving
Walls 3.3WK-1 2.0WK-1 84W 51W 79kWh £3.25 15kg
Windows 13.0WK-1 4.4WK-1 325W 110W 534kWh £23.54 98kg
Vent 4.7WK-1 0WK-1 118W 0W 228kWh £9.37 42kg
Total 21WK-1 6.4WK-1 527W 161W 841kWh £36.16 155kg

As you can see, most of the improvement actually comes from the windows and the ventilation. The thin layer of Kingspan K17 adds relatively little. This is because the wall was already insulated and the layer of internal wall insulation was very thin.

Was it worth it?

To be honest, the internal wall insulation probably wasn’t for the amount of extra work it involved compared to the energy savings. If you have to re-do your plasterboard anyway or you’re able to fit a more worthwhile thickness of internal wall insulation then go for it. I’ve canned any further internal wall insulation plans for rooms that simply need a lick of paint. On the plus side there’s a couple of cold bridges around the house that will benefit from applying the offcuts of Kingspan K17.

Apart from that, the room looks great and feels warmer and lighter and will make a really nice bedroom for the kids, so we’re chuffed with it.

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My new fusion-powered house

Posted in Green, Tech on March 1st, 2012 by Andy
Solar panels on the roof of my house

The sign of the modern-day sun worshipper

Powering your house with million-year old dead trees is so last century. What you really want is a toaster that’s fuelled by a massive ball of nuclear fusion!

With that in mind, I’ve had a 2kWp photovoltaic array nailed to my roof. The roof needed work anyway, and the window of opportunity for the government’s more generous level of Feed-in Tariff was about to close, so we thought “what the heck!” and got the cheque book out.

So far I’m really pleased with the amount of power it’s producing. It’s designed to produce 2oooW of power on a sunny summer day, but you get somewhat less if it’s cloudy or winter. Nonetheless it’s been putting out well over 20kWh of energy a week, which is pretty good going for Feb IMO. According to PVGIS it should produce about 1600kWh per year, and the idea is to try and grab as much of that as possible for use at home. That can be easier said than done, on a sunny day it easily outstrips what you can use at home. That’s not a biggy though, you get paid for all the power you produce, whether you use it yourself or not. As an investment I feel pretty happy that it should pay out quite well in the long run, it’s basically a government-backed, index-linked income for the next 25 years which is a lot better than you’ll get putting your cash in the bank these days.

Really happy with our installer too, both the PV dude and the roofers were excellent, so if anyone in Kent needs a roofer I can recommend a good one.

All-up it gives me a warm fuzzy feeling to be micro-generating, and it’s got my brain ticking over about knock-on projects. First up is a decent power monitoring system, probably a gnarly DIY solution like this. After that I’d like to look at optimising our use of the power we’re producing, probably something along the lines of automatically using hot water storage as a dump load. That could be bit tricky though, as we’ve got a combi boiler. Open to any suggestions on that one…

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How to Track Your Home Energy Use

Posted in Green, Howto, Websites on November 24th, 2011 by Andy

First of all, I admit it: data is geeky. But it can also save you a lot of money and reduce your carbon footprint.

As part of my drive to improve the energy efficiency of my home I’ve started tracking my energy usage through the site iMeasure. It’s a very handy site and free to use, plug your power and gas meter readings into it every so often and it’ll generate a load of stats about your usage.

After only a few readings it will have enough data to forecast your usage for the year, but by far the most useful trick it pulls is correlating your usage against data from the closest weather station. The point of this is that the amount of energy you’re using for heating is only really relevant if it’s compared to how cold it is.

A chart showing energy use against degree days

This iMeasure chart shows my actual gas usage at various temperatures. The blue regression line shows how efficient the heating system is. A more efficient system will have a shallower slope

It’ll also tell you how much CO2 you’re emitting through your energy use, and what your costs are.

Where the site really shines is if you’re making changes to improve your efficiency. There are ways to predict the effect of most measures, but there’s nothing better than seeing the change reflected in your actual usage.

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Is your house leaking money?

Posted in Green, Tech on November 4th, 2011 by Andy

Draftproofing your home is just as important to keeping it warm as good central heating and insulation are. Sorting your air leaks out can save you money and reduce your carbon footprint. But where to start?

Smoke drifting in the dark

A little bit of smoke could help keep you warm this winter

Leak testing

All homes are supposed to be tested for air leaks when they’re sold these days. Basically a dude comes to your house and fits a giant fan into the doorway, then measures how much the pressure inside changes due to the air leaks. The result goes on your Energy Performance Certificate, which rates the home’s carbon footprint. You can pay to have this done, but you’re looking at £200 or so, which is unlikely to be worth it.

You can approximate the procedure yourself if you have an extractor fan:

  • Close all windows and vents, mask over any remaining vents and air leaks with tape.
  • Turn off your heating and crank the extractor fan up to maximum.
  • Slowly go round your house with a smoke pencil or jos stick
The smoke will be pulled away from any air leaks which are letting air into the house. In particular check for:
  • Badly sealed doors and windows. Sort these with stick on draft strip.
  • Gaps around pipes under the sink, in the bathroom, and where any other pipes disappear into walls and floors. Squirt expanding foam into these.
  • Unsealed wooden floorboards are a carbon footprint nightmare. A mixture of wallpaper paste, newspaper and floor stain can fill the cracks.
  • Open chimneys or flues. If these aren’t being used seal them with a chimney cap or balloon.
Doing all this is cheap and easy, and just as important for your carbon footprint as more expensive and labour-intensive jobs like insulating your loft or getting cavity wall insulation or double-glazing. I recently went round and sealed up leaks I estimate were costing me £60 per year in heating. To do this I used a £5 can of foam, £5 worth of draft strip and about £10 worth of materials to seal my floorboards. Easy money, and a smaller carbon footprint.
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