Wood burner vs Gas stove running cost.

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Minkeycat
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Wood burner vs Gas stove running cost.

Post by Minkeycat » Tue 17th Nov, 2020 11:53 am

We need to change our woodburner to something less powerful and to keep our insurers happy. Does anyone know how the running costs of a 5kw woodburner would compare to the gas (LPG) fuelled equivalent?

TIA

CliffordPope
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Re: Wood burner vs Gas stove running cost.

Post by CliffordPope » Thu 19th Nov, 2020 4:29 pm

I can give you a comparison, but it's hard to make it meaningful by comparing like with like.

In the "summer" we cook using a gas stove running on 47Kg LPG bottles. We buy one a year, so that costs £59, but it only does cooking. Hot water is by immersion heater.

In "Winter" we use a solid fuel Rayburn running on logs, and that provides heat (kitchen, and to some extent downstairs bathroom and two other rooms), cooking, and hot water. That costs about £780. That cost also provides quite a lot of logs for the open fire in the sitting room. Occasionally we use the gas for more complicated cooking or in milder weather if we have delayed lighting the Rayburn.
There's obviously a big but variable overlap from day to day in Spring and Autumn.

So I don't suppose those figures are really very helpful. :)

Flyfisher
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Re: Wood burner vs Gas stove running cost.

Post by Flyfisher » Thu 19th Nov, 2020 8:01 pm

Based on this data: https://www.engineeringtoolbox.com/fuel ... d_169.html, dry wood will yield about 4.28 kWh/Kg whereas natural gas will yield about 13.1 kWh/Kg.

Based on this supplier https://www.engineeringtoolbox.com/wood ... -d_40.html, 3m3 of mixed hardwood costs £255 or £85/m3

The density of dry wood varies by species but let's use a figure of 650 Kg/m3 based on this data: https://www.engineeringtoolbox.com/wood ... -d_40.html, which gives us a cost of £85 / 650Kg = 13p/Kg, which will yield 13.1kWh or about 1p/kWh

I pay about 3p/kWh for mains gas, which suggests that a gas stove will cost around three times more to run than a wood stove for the same heat output, assuming both stoves are equally efficient.

I must admit I was expecting that bought-in wood would be more expensive than mains gas. Is my maths correct?

a twig
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Re: Wood burner vs Gas stove running cost.

Post by a twig » Thu 19th Nov, 2020 8:38 pm

Haven't looked properly but one thing pops out, you've assumed the metre cubed of wood is solid. Realistically with all the air when you buy a cubic
metre you should probably halve the wood you get for your £80.

Also I haven't been able to purchase a cubic metre of dried hardwood logs for much under £100 in years.

EDIT: These people sell stoves and reckon it's 10p kWh - http://www.gratefireplace.co.uk/blog/th ... explained/

paulc
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Re: Wood burner vs Gas stove running cost.

Post by paulc » Thu 19th Nov, 2020 11:51 pm

The proce one pays for logs varies quite a bit depending on where you are in the country. In East Anglia, a load, which might be two cubic metres is around £180. Once neatly stacked, you'd be lucky to get one cubic metre.
Wood makes sense for as long as you have a free or dirt cheap source of logs and somewhere to process & store them. If you are having to buy the stuff in ready to burn, gas, oil, or even coal is much cheaper in my opinion.

CliffordPope
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Re: Wood burner vs Gas stove running cost.

Post by CliffordPope » Fri 20th Nov, 2020 8:43 am

As I observed though, it partly depends what exactly your stove is doing. A "woodburner" normally does just that - it heats space, but nothing more. True, you can get ones that have a boiler at the back and heat hot water, but of course that's only useful if you run it enough to heat the water for all your needs. You can't cook on it normally, except perhaps heat a kettle or a small pan. So you'd still need gas for an ordinary cooker - they are not alternatives but complementary.

A rangecooker does everything, but not instantly, and not in summer :)

Wood is sold in all sorts of different measures, and it's hard to compare. I buy seasoned hardwood that has been stored in a big shed, and pay £185 per tipper load at summer prices. Stacked neatly it's probably something over 2 cubic metres.

Flyfisher
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Re: Wood burner vs Gas stove running cost.

Post by Flyfisher » Fri 20th Nov, 2020 12:02 pm

paulc wrote:
Thu 19th Nov, 2020 11:51 pm
The proce one pays for logs varies quite a bit depending on where you are in the country. In East Anglia, a load, which might be two cubic metres is around £180. Once neatly stacked, you'd be lucky to get one cubic metre.
Wood makes sense for as long as you have a free or dirt cheap source of logs and somewhere to process & store them. If you are having to buy the stuff in ready to burn, gas, oil, or even coal is much cheaper in my opinion.
I agree there is a huge variation in firewood quality and quantity. If sold by weight you have the moisture content issue and if sold by volume you have the ‘space’ issue. I’d certainly not suggest my calcs are definitive, but I was surprised myself at the result even allowing for a large variation as I’d also thought mains gas was a cheaper form of heat than bought-in firewood. Indeed, I’ve always thought of mains gas as THE cheapest fuel available. Hmm.

ElectronicFur
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Re: Wood burner vs Gas stove running cost.

Post by ElectronicFur » Fri 20th Nov, 2020 6:11 pm

One thing I would look into before switching to a gas stove, is how much humidity the stove releases.

As it happens I have just today been monitoring the humidity levels in our study, which has an open gas fire in it. When the fire is on, the absolute humidity rises, so I think burning the gas is adding moisture into the air. The absolute humidity went from 9 g/m2 to 11 g/m2 after one hour.

So whilst convenient, I'm thinking I'd rather have a wood burner in there.

a twig
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Re: Wood burner vs Gas stove running cost.

Post by a twig » Sat 21st Nov, 2020 7:46 am

Well yes, burning gas produces water vapour as a "waste product" so you will be adding moisture to the room, unless it's a closed fire and all the waste goes up the flue.

Minkeycat
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Re: Wood burner vs Gas stove running cost.

Post by Minkeycat » Sat 21st Nov, 2020 10:19 pm

Many thanks all. This is very interesting. We do like the woodburner but we're thatched and I have to say I'm a bit peeved because we recently paid nearly £3,000 to have the chimney lined and a new pot etc to make it conform to the latest regulations so, for instance, the top of the chimney was 120cm above the thatch. This was so just we could start using the woodburner that was installed nearly 20 years ago and never used by the previous owner! We've just had the insurance renewal and this year I'm told the insurance industry have decided, based on no information, that the top of the chimney must now be 180cm above the thatch which will require planning permission, new pot and new liner (and which will look utterly ridiculous). Without complying, we're down to one insurer in the whole country who'll cover us (although I found another one within 2 phone calls) so they've got us over a barrel.
My thoughts are that we have a perfectly good liner up which we could potentially vent a gas fire so we could still have the character of flame but would venting a gas fire like that take moisture out too? I don't know how gas fires work. It doesn't need to be hugely powerful, would presumably allay the "fears" of the insurers as there wouldn't be sparks to land on the thatch and the house would remain looking like a nice little cottage rather than looking like someone's put a tin mine on the roof! It would also be less hassle than logs so there are advantages. We only light a fire at weekends but a fire feels somewhat necessary in a house like this. It would have to be LPG though because we're not on mains gas here. If we can get gas in, it means we can stay in the house that we love but with the insurers niggling away like this, it's putting the idea of moving into my head.

paulc
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Re: Wood burner vs Gas stove running cost.

Post by paulc » Sun 22nd Nov, 2020 12:01 am

It might be possible to fit a rigid stainless steel extension to the top (or bottom) of the existing liner. That would save on the cost of having to rip the whole thing out and starting from scratch. Not sure if planning permission would be required - That would need to be checked with the local council.
If you used a sealed gas fire, fumes and condensation would all go up the chimney. Whether you could reuse the existing liner would depend on the size, what diameter the new fire requires, and the opinion of the installer.

88v8
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Re: Wood burner vs Gas stove running cost.

Post by 88v8 » Sun 29th Nov, 2020 9:49 am

Even after raising their height our chimneys have less than 6ft freeboard, we have two 8kw (nominal) woodburners, and I only have them swept once, not twice as insurers insist.

The insurance aggravation has been increasing year on year, and last year when our insurer told us they could no longer cover woodburners in a thatched house, I decided not to bother with insurance any more.
However, I did buy a ¾" hose for reach end of the cottage.

We get through about 3-4 tons of wood a year, cost maybe £500. Plus that's 3 tons to be chopped up, stacked in the woodhouse, lugged up a long flight of steps. Make up the fires each morning, ashes. Not sure I'll be doing that in ten years.

As a rule, we light up in the early evening, the one in the dining room first, then after dinner we let that diminish, and light up in the sitting room.
We need the evening heat as our storage heaters run down.

This year, it's only this last week we've really started lighting up.

Cost-wise, given that you only run the fire at weekends, it doesn't really matter, does it? And you'll save all the unnecessary 'improvement' work the insurers want.
If you'd be happy with a gas version, I'd go for it. You can sell the woodburner on eBay.

The insurance aggravation will only get worse.
Thatch is an unbalanced portfolio, it only takes one fire to wipe out a year's profit.
Many owners don't run their stoves properly; they don't have a thermometer, they burn any old wood seasoned or not - I've seen posters on here confessing to burning old pallets and other softwood - they leave the woodburner unattended so it overheats, they burn solid fuel in wood-grade liners. One can hardly blame the insurers for losing patience.

Question is what you will do when Nanny Gubmt decides that gas will be banned. But we'll leave that for another day.

Ivor

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