Saving money on heating – 2

This is an expansion of the previous post, as it seems I have more luck with a wood stove than the general experience.

Saving energy seems to be all the rage these days, it isn’t just me, both the Grauniad and the Daily Fail seem to be at it. Looking at the scepticism in the Grauniad article comments, it seems not everyone can make a wood-burning stove work for them from a financial viewpoint.

My experience is most definitely that a wood burning stove can reduce heating bills. Indeed, if I could think of an intelligent way to go about hot water I could bring my gas bill down to just cooking; I managed to avoid running the central heating at all last year, but I didn’t particularly want for heat.

I figured it would be interesting to revisit this, to bring out the parameters that enable me to heat the whole house, which seems key to transforming a wood burning stove from lifestyle accessory to money saving tool. I have to admit that I bought the stove as a lifestyle accessory in the easy party times before I realised I wanted to retire early, so I am sweating an existing asset ๐Ÿ˜‰

#1 Don’t own too much house

I had a rough experience with negative equity early in my house owning career. This has made my vision of a house very different to that of most of my fellow Britons. I do not have a deep existential belief that property always goes up in value.

Sarah Beeny and the rest of Britain may believe houses always go up, but I don’t, because I know otherwise from personal experience

As a result I didn’t stretch myself to the maximum mortgage I could get after that first one, I bought as much house as my living requirements wanted. As a single man I bought a two-up-two down, because that was all I could afford. When I bought this house, with DxGF we went for a three bed semi, which suited us about right, and it suits my current living arrangements right for DW and I.

It is small compared to the houses of many of my work ex-colleagues, many of whom subscribed to the mantra of buying lots of house because it made them feel good about themselves, and well, y’know, housing always goes up so it’s a great investment too. Good luck to them, and obviously with kids you need more than the one spare room we have. Somewhere between when I grew up and now, we also collectively decided that children each had to have their individual bedrooms, which obviously puts the pressure on families as we increasingly live separate lives.

Nationwide house price index. House prices never go down, well, until they do.

Over a thirty-year plus house owning career the price of a house probably does go up in real terms, but the change is not smooth or monotonic. There be switchbacks in the housing market, and woe betide you if you buy and take a switchback at the same time as some bad luck. If you can sweat it out that’s great, but lose your job or need to move at the wrong point in the cycle and you are exposed to negative equity. I cannot describe the soul destroying feeling of paying down a mortgage on a house you’ve sold for less than the mortgage…

What’s that got to do with heating? It’s a damn sight easier to heat a small space than a big one ๐Ÿ˜‰ Heating a modest house is always going to be easier than heating a McMansion, all other things being equal. That is not the only extra cost of a larger house, you also have to clean, furnish and decorate the extra space too.

FWIW some people claim you can get round having too much house by just heating part of it. Don’t do that for long periods. You may be able to get away with it in drier parts of America but not in the damp of a British winter. You need both ventilation and some heat in a house otherwise condensation will get you, and you’ll have to redecorate that room in Spring ๐Ÿ˜‰

#2 prize features in the house that help you save energy

The trouble with these are you have to do this before you buy the house. I was lucky in getting a collection of features that worked well with a wood burner, but it may be of value to call them out.

The principal disadvantage of a terraced house or semi is you get to hear your neighbours, so you want to avoid choosing a house next a young couple of child-bearing age ๐Ÿ˜‰ I should have jumped to that with my first house. On the upside, you get to use some of their heat on the party wall, which is a quarter of your wall area. Although it’s probably a significant effect it isn’t make or break. In an ideal world I’d like to live in a detached house, and would look to retain some of the following features:

Cavity walls

wall temp upstairs

My house was already cavity wall insulated, which is something else to look for, but it had crappy single glazing which I put up with for far too long. The actual cost of changing this wasn’t too bad – I had a grossly inflated expectation of the cost which is why I stalled it for a long time. I’d buy a house with single glazing over one of a similar size that didn’t have cavity walls any time. I’d go as far as not having cavity walls would be a dealbreaker for me in any future house purchase unless power costs came down a lot. Retrofitting cavity insulation is cheap enough, andย  you can do something about single glazing, but insulating solid walls is very, very dear it seems. Having lived with both, solid walls are comparatively cold in winter, and seem to increase the thermal delays of the house. That’s bad for the typical work pattern of non-occupation during the day, unless you can reduce draughts so the heat isn’t lost in the day. That doesn’t usually go with the sort of house that has solid walls, because of their age.

Central chimney

the chimney wall temperature is 22C, 2C higher even after the stove has not been running for more than 12 hours overnight

If you are going to use a stove that is, obviously irrelevant if you use gas central heating. You want to use that precious heat all for yourself. You don’t want to share half of it with the neighbours, or even worse do your bit for global warming by sharing it with the great outdoors.

The chimney in my house goes up the middle of the house. As such the flue runs past the bedroom wall and the wall of my den (the second bedroom) and the heat does warm the walls and the room perceptibly – though with a latency of several hours. As shown, the temperature of the chimney breast upstairs is 2C higher than the adjacent wall, so it is effectively a low-temperature radiator about 0.5m by 2m area. This is measured 12 hours after the stove has stopped running, outside temperature was about 14C.

That’s good in practice, we tend to start the fire when the sun goes down and the first floor is perceptibly warmer the next day than the ground floor. Which is great, it works with the usage pattern of the space. I would also favour a house with a chimney running through the middle of the house in a future purchase, assuming it were a two-storey house.

Of course you don’t get character with a house like mine. This sort of thing doesn’t particularly trouble us, but from TV shows it seems this matters to many people, not just Sarah Beeny ๐Ÿ˜‰ In general you need more energy to heat a house with character because they tend to be more draughty and have solid walls, this is all part of the complex tradeoff you have to make when choosing somewhere to live. Having a significant heat gradient from the room to the fire does make things feel more homely, as it draws people together, and probably panders to some atavistic memory of our forebears in front of the fire. Not for nothing does the cat curl up in front of the fire rather than the radiator. That is also part of the character of a place, I love it when we go away to somewhere in the winter with a massive open fire in a huge inglenook fireplace with a heat gradient thatย  made us feel cosy in the warm space. However, I wouldn’t like to pay for it every winter day.

#3 Insulate and draught-proof first

The great thing about insulation is that it’s cheap, and a reasonably easy DIY win. I only have three inches of loft insulation, and a reasonable amount of junk up there. Go for more than 3 inches and you can’t use the loft for storage since 3 inches is the typical depth of the rafters. In a modern house you can’t store much in the loft anyway, because of the cheap prefab woodwork cluttering up the loft. Although I only have three inches of rockwool and the current recommendation is for more than twice that, the loft boards and the junk probably help. It’s damn cold in the loft compared to the house in winter ๐Ÿ™‚

Draught-proofing is best done in double glazed windows using integral rubber seals, but you can DIY here, though none of the DIY solutions last more than a couple of years. They are at least cheap DIY. Doors are also a problem. For me the double glazing fixed draughts almost totally (there is a porch and old conservatory that keep draughts from the main front and back door). I believe nutting draughts is a major part of why I can avoid using the central heating, because the house can hold the heat from a fire in the evening almost through to the next afternoon.

My previous Victorian two up two down had individual room gas fires. For a gas fire to work it has to be open to the outside to vent the flue and open to the inside for the heat to get out. No complaints about the efficacy of the gas fires, but the house would not hold heat from the evening to the morning, let alone the afternoon. It was always brass monkeys in the morning, and that’s a bastard for getting up to go to work.

In the current house I didn’t notice the problem of the house not holding heat, because like most people I’d set the central heating to come on a bit before it was time to get up. So that solved the problem with the brass monkeys, but the leakage of heat meant the wood burning stove couldn’t work well for the whole house – it had the same problem as the previous house, it was freezing in the morning. So I used the central heating just for the morning. This combination reduced the gas bill, but what transformed things was fitting the double glazing. That allowed the wood stove to take over the heating of the whole house. The stove is a small one with a rated max output of 6.5kW. In all fairness to the installers, it was only specified to heat the front room, which it was easily able to do despite the initial draughts, and those draughts were hardly perceptible to me. It’s extremely necky to then pitch for using a single room heating appliance to heat the entire house, but it works for me.

So the takeaway is that you can heat your house with a log-burner alone, as long as the house isn’t too big, as long as you have dealt with insulation, double glazing and draught-proofing properly first. Insulation and draughtproofing are relatively cheap to do compared to installing a log burner. I’ve probably spent ยฃ10k on windows and the log burner combined. It’s hard to say where the break-even point is. The windows have probably added something to the value of the house, if only because the previous ones were obviously ropey. If I say the total outlay is ยฃ8k allowing for that then the breakeven point is about 8 years or so, shorter if gas prices rise faster than inflation.

various other related issues

My gas boiler is over 20 years old, and a modern one would undoubtedly be more efficient. I have savings allocated to replacing that, but I am putting that off because there seem to be very serious reliability problems associated with condensing boilers which is the only type allowed to be fitted these days. The problem seems to be the extra complexity, and the condensate has to be discharged outside, and there is a problem with the discharge pipe freezing so the condensate backs up and the safety system shuts down the boiler. A heating system that doesn’t like freezing temperatures outside isn’t the greatest triumph of engineering smarts IMO. On the other hand, I would benefit from a modern pressurised on-demand hot water system without storage. Downsides of that are I have mixed feelings about the lack of resilience against interruptions to the mains water supply that I expect to be increasingly likely as we have interruptions to the mains power supply. The 25 gallon cold water tank in the loft gives some peace of mind there ๐Ÿ˜‰

Since I don’t use the boiler for heating I can eat the lack of efficiency, and I haven’t come to a conclusion about the hot water. Losing the storage tanks would KO any opportunity to use solar hot water, and I could probably halve the dwell time of the boiler by changing the primitive mechanical programmer for a modern electronic one to get just one heating period for hot water a day rather than the two the current programmer insists on. You probably need that for a four-person family but it’s overkill for the two of us most of the time.

All round, saving money on energy/heating demands a whole systems approach and a reasonably methodical process before you do anything, and the opportunities may well be constrained by the design and size of your house.You have to start with what you have and work with it, and unfortunately the main issues are the size and design of your house, which you’re pretty much stuck with.

Running a 25 year old boiler and a modern wood stove isn’t the obvious way to attack this, but it works well enough for me, my combined gas and electricity bill is ~ยฃ500 and I believe they are still significantly overcharging me on estimated consumption. This is less than half the typical UK power bill, and it is notable that about a third of it is the fixed standing charges.

I was lucky with some of the features of my house, but only realised the benefits once the last link had been completed of the insulate and draughtproof chain, which was replacing the windows. Unfortunately, it looks like you have to get everything to work together before you can use a wood burning stove for the main or only heat source. Mine is only 6.5kW flat out. Using this calculator a replacement whole house boiler for my house would need to be 17kW with typical assumptions. The improved heat holding capacity I’ve ended up with probably explains why a wood burning stove works for me. I can leverage the investment by using it to replace my heating gas consumption, shortening the break-even period.

Looking at all the grousing in the Guardian comments, many people buy wood stoves as a lifestyle acessory, and there’s nothing wrong at all in that. It is then a lifestyle cost, not a way to save money, even though some of the cost is defrayed by reduced gas usage. It’s reasonable to allow for that but it won’t pay for it.

Bear in mind that in the UK people typically move house every seven years so the opportunity for cost recovery is limited. I’m unusual in that I stayed in my first house ten years and have only moved once, I’ve lived in this house for 14 years and don’t have any current plans to move, soย  I can expect to reach breakeven and into the free lunch beyond.