Fisher Stove -Grandma

Millwright · Sep 8, 2014

Greetings all across the pond, this message is sent from little old England where I have stumbled across a Fisher Grandma stove in a scrap iron yard. I have renovated the stove but in order to comply with UK laws I need to know to heat output rating in BTUs or Kilowatts so I can calculate the air intake requirements. I know the Grandma stove is said to be rated at 1500 sq feet, but how do you convert this to a energy rating please?

Many thanks for any advice you can offer,

Steve

Shwammy · Sep 8, 2014

Unfortunately they weren't ever rated for BTU's. You can use a conversion chart, sort of a back end way of figuring it out. It's around 80,000 BTU's as a guesstimate after looking at a chart. Just search for "square feet to BTU calculator".

Millwright · Sep 14, 2014

Shwammy said:
Unfortunately they weren't ever rated for BTU's. You can use a conversion chart, sort of a back end way of figuring it out. It's around 80,000 BTU's as a guesstimate after looking at a chart. Just search for "square feet to BTU calculator".

Hi Shwammy,

Many thanks for your reply - most appreciated. I'm curious, how do you in the States go about calculating the intake requirements for a fisher stove if you don't have a manufacturer's BTU rating? In the UK the law is quite prescriptive on size of permanent air openings/vents for stoves.

Best regards from across the pond...

Steve

Shwammy · Sep 14, 2014

We don't. If you live in a mobile home you must install a stove that is capable of using an outside air source. In a nutshell that's all there is too it.

Grisu · Sep 16, 2014

Millwright said:
Hi Shwammy,

Many thanks for your reply - most appreciated. I'm curious, how do you in the States go about calculating the intake requirements for a fisher stove if you don't have a manufacturer's BTU rating? In the UK the law is quite prescriptive on size of permanent air openings/vents for stoves.

Best regards from across the pond...

Steve

Stoves here are emission tested to a max of 7.5 g particulate/hr and the minimum air opening is set by the manufacturer to stay below that threshold. Older (pre-EPA) stoves have been grandfathered in. Not sure what regulation in the UK are regarding emissions and burning in older, less efficient stoves. Maybe ask a local chimney sweep.

coaly · Oct 19, 2014

Steve;
I knew I had a "Woodburner's Calculator" here and finally found it.
It's a nifty cardboard slide rule type calculator that is used for figuring BTU Output needed by cubic feet in different temperature zones of the US. On the back is also a calculator with surface temperature and surface area (square inches) that gives BTU / Hr. and Watts. A manufacture rating is calculated with a specified surface temperature, (which wasn't done back then) where real world output will vary with the surface temperature at any given time. So the keyword in your question is "manufacturers BTU rating".
I can give you the actual output in BTU / Hr or Watts when the surface temperature and square inches of heating surface is known.
Here's what the back of the calculator looks like set randomly to 400* f. at 2000 square inches that shows a total of 13,000 BTU or 3800 Watts.

If you give me the square inches of heating surface and average temp you run, I can give you exact Watts at that output. The maximum temp you run would be the temp to use for max output to calculate maximum air required. It would be good to know what your normal vs. maximum is.

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Fisher Stove -Grandma

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