[Greenbuilding] Wood Heating Experience & Exterior Wood Boiler charging Thermal Tank for Radiant Heat

Corwyn corwyn at midcoast.com
Sat Dec 24 10:12:50 PST 2011


On 12/24/2011 12:42 PM, Sacie Lambertson wrote:
> /If you have a drafty house, you need to keep the fire going to maintain
> somewhat even temperature. _ However, with a tight house, a hot
> intermittent fire heats the house and the house holds the heat._/
>
> Would this assertion be true regardless of the size of the house?  Or
> the size of the stove?

Those aren't the really relevant characteristics, nor is tightness 
alone.  The relevant ones are 1) Heat loss of the house (all forms, 
conductive, convective, and radiant); 2) The thermal mass of the house. 
  The lower the first and the higher the second, the greater the time 
constant, and thus the longer it will take to cool down after being heated.

In general, larger houses will have larger heat losses.  In general, 
smaller stoves will achieve their maximum efficiency with a relatively 
smaller fire.   A well insulated and tight house, with a low thermal 
mass will require more frequent, smaller fires in order to avoid 
overheating.

Let's say you start with a house that loses 50,000 BTU / hour, and has 
thermal mass of 10,000 BTU / degree.  This means you are losing 5 
degrees per hour, and probably need to turn on the heat every two hours. 
  Now, if you double the insulation and half the air leakage, you will 
be losing 25,000 BTUs / hour (or 2.5 degrees per hour) so can go for 4 
hours without heat.  If your wood stove puts out 100,000 BTUs / hour, 
and you can make fires in one hour increments, a fire will last 4 hours, 
however, the swing of the temperature in the house will be 10 degrees. 
If you then double the thermal mass in the house, you will still be 
using the same amount of heat, but the temperature swings will only be 5 
degrees between fires (every 4 hours).  And so on.

[numbers above are completely made up, for ease of calculations]


Thank You Kindly,

Corwyn

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.greenfret.com/
topher at greenfret.com
(207) 882-7652



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