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Our stove: how do I estimate its heat output?


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Nominally, I know the rating of the stove (5kW) in our current house, but I guess that most of its output goes into warming the arses of the local sparrows.

Readying the house for sale, or maybe rent, I appreciate that most people aren't as devoted as I am in terms of paying daily homage to the fiery monster in the inglenook. The stove has a back-boiler, and it does a spiffing job of producing super-heated-close-to-boiling-water every night ready for SWMBO's bath. It provides heat for a few scalding radiators too. So much so that it's a good deal safer to touch them if there's a bit of air trapped in the rads.

 

There's no way any purchaser or renter is going to tolerate that. How do I guess -or work out even- how much electricity (or kWH) of electricity I need to produce  the same (or slightly less) 'comfort'?

 

I know exactly how much anthracite we have consumed over the years (2 bags per week in't season). Is it possible from that information to work out how many kWh I have put in? And then make a guess at the number of kWh has gone into warming the local sparrows? And thus derive the number of nice clean kWh of E7 I will need?  (Gas isn't a possibility).

 

I am aware of @JSHarris calculator (and other online calculators), but I wanted to check those results against a reverse-engineered number

 

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Having just read another thread about how to put temp sensors in a slab, my mind quickly produced a picture of a plastic sparrow on Iain,s chimney with a probe up its a***. ?

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Anthracite has a calorific value around 9.2kWh per kg. True efficiency of a closed stove could range from 20% to 80%. Without supporting evidence I would tend to the bottom half of this range.

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48 minutes ago, gravelld said:

It would be interesting to know the test process stove manufacturers go through to derive the efficiency figures, assumptions made, and so on.

 

EN 13240 if you want to look it up...

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52 minutes ago, gravelld said:

It would be interesting to know the test process stove manufacturers go through to derive the efficiency figures, assumptions made, and so on.

I've seen maybe 20 stoves up at our hutting fraternity. In general...cold weather, poor insulation...folk want maximum output.

My observations are that new stoves which equals very expensive; are fantastic to look at ( big glass and slow flickering burn) but don't pump out much heat. No great surprise as most have ceramic or fire brick lining on the inside to aid the fire temperature so less heat radiating through the stove wall.

Mine on the other hand was £250 from machine mart and rated at 11kw.

Probably because it's just 4 bits of cast iron bolted together. However it is fantastic for keeping the place toasty. Internal temperature is regulated by a combination of fuel type, control of the rudimentary stove vent and choosing which windows to open and how wide.? I'd call it stove art.

IMG_20160925_120111216.thumb.jpg.5e7e61250ddcc798669562d17bc11f82.jpg

Putting it in the middle of the floor must help too, instead of heating up the inglenook walls...horses for courses passivers?

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How much do you want to spend, and how much time do you want to spend on it.

You could buy a few temperature sensors and wire them into a Raspberry Pi.  Then log the temperature differences between the input air, the output gasses, the water input and the water output.

Or just use a cheap infrared thermometer to do the same thing.

Keep a record of the mass of anthracite you use for each burn.

Fair bit of number crunching at the end, but simple enough to set up in a spreadsheet.

http://www.engineeringtoolbox.com/boiler-efficiency-d_438.html

You can possibly compare the amount of losses up the birds arse with this.

http://www.engineeringtoolbox.com/fuels-air-flue-gas-d_170.html

And

http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html

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@Tennentslager Are you saying your cheap Machine mart stove is just a "tin box" with no fire bricks to line the fire box?

 

I am thinking SWMBO is thinking of a WBS for our static 'van, but I don't like the idea of one with no fire bricks as surely the sides and back will get much hotter?

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43 minutes ago, ProDave said:

@Tennentslager Are you saying your cheap Machine mart stove is just a "tin box" with no fire bricks to line the fire box?

 

I am thinking SWMBO is thinking of a WBS for our static 'van, but I don't like the idea of one with no fire bricks as surely the sides and back will get much hotter?

Yes.

My stove thermometer is on the flue about a metre up...usually sits at 200 for dry wood moderately stacked. 100 for coal ticking over.

It's a cast iron cylinder (okay it's got a couple of baffles for the exhaust gas) with a door. 

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10 hours ago, A_L said:

Anthracite has a calorific value around 9.2kWh per kg. True efficiency of a closed stove could range from 20% to 80%. Without supporting evidence I would tend to the bottom half of this range.

 

Sorry but this statement doesn't seem consistent with the physics.  Inefficiency could be defined as the percentage of heat energy lost out of the system, and the system here is the house interior.  There are two main sources of heat loss: heat carried in the gas stream, and (in the case of wood) latent heat of evaporation.  Wood burns inefficiently because it has a high moisture content and this water has to be boiled off, and the remaining lignin and cellose has a reasonable low energy density, so unless wood has been air dried for at least 2 or 3 years then most if the energy goes into boiling its water content.  This isn't the same for coal or coke.

 

The other thing is if the chimney is internal to the house, then a lot of the heat is lost inside the house and goes to heat the upper storey.  A decent sealed stove only allows enough air through to oxydise the coal and I know by putting my hand in the gas stream coming out of the chimney, in our farmhouse that it ain't that hot. Maybe 40°C. So I would have expected the system efficiency of a decent multifuel stove burning coal or smokeless to be nearer the 80% end.

 

The carbon contribution is a completely different matter?

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13 hours ago, Trw144 said:

 

EN 13240 if you want to look it up...

 

Hmmm. So it costs £244 to read the standard which is supposed to protect me? Before I get all self righteous, in what way is that democratic?

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15 minutes ago, gravelld said:

Hmmm. So it costs £244 to read the standard which is supposed to protect me? Before I get all self righteous, in what way is that democratic?

See if your local library can get hold of a copy.

They get some of them down here.

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18 hours ago, Tennentslager said:

I've seen maybe 20 stoves up at our hutting fraternity. In general...cold weather, poor insulation...folk want maximum output.

My observations are that new stoves which equals very expensive; are fantastic to look at ( big glass and slow flickering burn) but don't pump out much heat. No great surprise as most have ceramic or fire brick lining on the inside to aid the fire temperature so less heat radiating through the stove wall.

Mine on the other hand was £250 from machine mart and rated at 11kw.

Probably because it's just 4 bits of cast iron bolted together. However it is fantastic for keeping the place toasty. Internal temperature is regulated by a combination of fuel type, control of the rudimentary stove vent and choosing which windows to open and how wide.? I'd call it stove art.

IMG_20160925_120111216.thumb.jpg.5e7e61250ddcc798669562d17bc11f82.jpg

Putting it in the middle of the floor must help too, instead of heating up the inglenook walls...horses for courses passivers?

 

Where are the Sheriff and the Enamel Mug?

 

F

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Suspect that for all the accuracy you will get you can estimate the amount it puts unto the room by leaving it off and putting a stack of heaters on top,until it feels the same, then count the heaters.

 

Leaving a stove to tenants is playing with fire xDxDxD:D.

Edited by Ferdinand
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13 hours ago, recoveringacademic said:

 

Oh Scheisse! Hadn't thought of that.

 

It does depend on who they are, and so on. I have Ts who I would trust and wouldn't, but i wouldn't fit one on the basic precautionary principle. If you are seriously looking at rental you could invite a Council Person to comment before you start.

 

Smoke damage to house if they leave door open etc.

 

But many modern people, never mind tenants, struggle with stuff more basic than that.

 

All the 100 pages of rental paperwork will be good firestarters, mind.

 

Ferdinand

 

Edited by Ferdinand
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Can't you simply replace the WBS+BB with an oil fired unit?

Simple, cheap enough to run, and idiot proof ( if your making sure they don't run out of oil that is ). How would you integrate E7 / E10 other to provide heating ? Would you fit an electric boiler ?

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