What makes stoves so efficient?

[Khriss]

29 minutes ago, openspaceman said:

That's efficiency of converting your labour into heat rather than the efficiency of converting chemical energy of the log into heat which we were discussing.

Indeed . Basically it's how dry yr wood is - water requires a huge calorie conversion, more than cement from my distant O level Chemistry remembering. So it's that that will be yr overall loss in combustion. K

[openspaceman]

2 hours ago, Khriss said:

Indeed . Basically it's how dry yr wood is - water requires a huge calorie conversion, more than cement from my distant O level Chemistry remembering. So it's that that will be yr overall loss in combustion. K

Yes it takes energy to boil the water off before the log will burn but it's not a large proportion of the energy in the log, the  problem is more that it reduces the combustion temperature and the knock on effect of that is  worse pollution given off. Even burning bone dry wood produces steam in the flue as the hydrogen in the wood turns to water.

 

Comparing it with cement is very apples and oranges

[Big J]

I'm not sure that a stove is really that efficient. 

 

We've had a few stoves over the years, and for the past 5 years we've had two different 20kw stoves. Over that time we've averaged about 37 cubic metres (loose) per 12 month period. I deliberately don't use the term winter as where we were in Scotland you'd rarely have a month pass without the fire being lit at some point. 

 

20kw might seem like a lot, but the boiler for the last house was 28kw. I'm efficient at burning wood - I religiously use a flue thermometer and never run it too hot or cool. A friend of ours has a doctorate in thermography and thermal imaged our old house and he said for it's age that it's quite heat efficient. New house isn't quite as cool but the climate is milder here in Devon.

 

With all that in mind, we're reliably a barrow a day with winter weather. Not a small barrow at that. If the temperature is below 10c, we're doing about 3.5 cube a month and when you see two years worth stacked up at the back of the house you start thinking you're a bit mad for not just filling up the oil tank. 

Edited January 6, 2019 by Big J

[Woodworks]

19 minutes ago, Big J said:

I'm not sure that a stove is really that efficient. 

 

 

 

Not meaning to be rude Jonathan but your choice of a stove is not exactly the hight of efficient design. If I remember right you like the Champion stoves which just appear to be a metal box you chuck logs into. Great value on the face of it but they may well not be getting the hot enough to burn all the gases so plenty more to be had from the wood. Our current 7kWh stove which is not exactly state of the art but it can still manage to heat the whole house. If we used that exclusively I estimate we would need 8 cube per season. 

[Big J]

2 minutes ago, Woodworks said:

Not meaning to be rude Jonathan but your choice of a stove is not exactly the hight of efficient design. If I remember right you like the Champion stoves which just appear to be a metal box you chuck logs into. Great value on the face of it but they may well not be getting the hot enough to burn all the gases so plenty more to be had from the wood. Our current 7kWh stove which is not exactly state of the art but it can still manage to heat the whole house. If we used that exclusively I estimate we would need 8 cube per season. 

I actually rated the Champion Stove Company stove higher than the one that we have at the moment. We have a Woodwarm 20kw double sided stove which would have been over £2k. We've still burned about 14 cube on it so far this winter. And that's with me letting it go out on the milder days. Living room and downstairs is 20-22c and the upstairs is 16-18c. Not excessive, and just the nature of heating these crappy old buildings.

[Woodworks]

11 minutes ago, Big J said:

I actually rated the Champion Stove Company stove higher than the one that we have at the moment. We have a Woodwarm 20kw double sided stove which would have been over £2k. We've still burned about 14 cube on it so far this winter. And that's with me letting it go out on the milder days. Living room and downstairs is 20-22c and the upstairs is 16-18c. Not excessive, and just the nature of heating these crappy old buildings.

Eeek!  Yes, I am a big fan of Woodwarm stoves. My folks 12 kWh one is probably the best stove I have ever used. If the Champion ones are better than them I will eat my hat (easy to say as I never wear one)

 

Edit. Maybe being double sided they are not as well insulated with glass both sides. Some thin double glazing cant be a match for 25mm or vermiculite board so maybe still not getting hot enough?

 

Edited January 6, 2019 by Woodworks

[Big J]

1 minute ago, Woodworks said:

Eeek!  Yes, I am a big fan of Woodwarm stoves. My folks 12 kWh one is probably the best stove I have ever used. If the Champion ones are better than them I will eat my hat (easy to say as I never wear one)

They are much simpler stoves and the glass won't stay clear in the same way, but the heat output was always superb. The way that the fire seemed to burn (front to back) meant that it was very easy to overnight on softwood (without slumbering the fire). You'd get 16 hours plus out of it on the denser hardwoods. It wouldn't smoke in normal operation and I have a couple of friends that put a lot of wood through theirs in smoke controlled zones without anyone noticing.

 

When we took the stove out when we moved, there was minimal ash from the chimney and we didn't sweep it for the duration of our stay in that house. 5 years and some 180 odd cubic metres burned. 

 

I just prefer big stoves with a front to back log loading construction. 2ft logs all day long, minimal processing and maximal heat. I do appreciate that for a properly insulated house that it's total overkill, but we've not living in a house with modern insulation thus far.

[openspaceman]

32 minutes ago, Big J said:

but we've not living in a house with modern insulation thus far.

In which case you will burn a similar  amount of energy in oil.

 

As I said earlier energy released has to be accounted for, it either goes up the chimney as hot smoke, remains in ash pan as unburnt fuel or it enters the room and is dissipated through roof, walls, floor, windows and vents.

 

In point of fact if the glass blackens the combustion is incomplete which means chemical energy is lost as carbon monoxide and other PICs and of course a decent gas or oil condensing boiler will have a flue gas temperature of less than 100C whereas not many stoves will be lower than 200C which represents a significant loss even with a clean burn.

 

 

[billpierce]

I actually rated the Champion Stove Company stove higher than the one that we have at the moment. We have a Woodwarm 20kw double sided stove which would have been over £2k. We've still burned about 14 cube on it so far this winter. And that's with me letting it go out on the milder days. Living room and downstairs is 20-22c and the upstairs is 16-18c. Not excessive, and just the nature of heating these crappy old buildings.

Hope you do get sorted with a new build sometime j. Few pals have build nice wooden well insulated houses, was round there new years day and it was still cosy as owt at 2 in the afternoon, no fire been lit since the night before and no other heating. I couldn't believe it. In out draft stone small houses it's the first thing to do every morning!

[Big J]

10 minutes ago, billpierce said:

1 hour ago, Big J said:

I actually rated the Champion Stove Company stove higher than the one that we have at the moment. We have a Woodwarm 20kw double sided stove which would have been over £2k. We've still burned about 14 cube on it so far this winter. And that's with me letting it go out on the milder days. Living room and downstairs is 20-22c and the upstairs is 16-18c. Not excessive, and just the nature of heating these crappy old buildings.

Hope you do get sorted with a new build sometime j. Few pals have build nice wooden well insulated houses, was round there new years day and it was still cosy as owt at 2 in the afternoon, no fire been lit since the night before and no other heating. I couldn't believe it. In out draft stone small houses it's the first thing to do every morning!

We'd be far better off in the UK funding much improved building than RHI or FITS. The founder of the architecture practice my wife used to work with in Edinburgh said that many of the methods of producing sustainable power on a small scale were not actually sustainable as the payback period exceeded the effective working life of the device. That was nearly 10 years ago though. It has changed a bit since then. However, an airtight and well insulated house is 10 times better than a house of typical insulation and micro power generation (or Eco-bling, as my wife's boss used to call it).