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re: wood stove water heater
7 oct 1998
georges wrote:
>i'm trying to preheat the water into an electric hot water heater
>using the heat from a wood stove... i wrapped a 1/2 inch tube around
>the 6" diameter stove pipe ( 9 turns around the stove pipe). flow
>through the water tube is induced with a laing circulating pump,
>which runs about 3 gpm.
a btu can heat a pound of water 1 f, so heating 50 gallons of water
from 50->110 f at 8 pounds per gallon requires about 24k btu, and
3 gpm is about 1500 pounds of water per hour which could move say,
30k btu/h of heat with a 20 f temperature difference. sounds good.
>...the flu temperature is about 500 degrees f...
getting 30k btu/h from the stove into the water through a water film
thermal conductance of about 60 btu/h-f-ft^2 and a 300 f temperature
difference requires about 30k/60/300 = 1.7 ft^2, eg 13 feet of 1/2"
500 f copper pipe, about 4 spaced turns in a flat 1' spiral.
>...i'm looking for a method to better connect the copper tube to
>the stove pipe. any recommendations?
why not lay some chicken wire or hardware cloth on the stove top (a
better thermal conductor than the stovepipe), and lay the copper pipe
over that, with more wire on top to avoid cracking, then fill the
sandwich with an inch or two of sandcrete?
you might not need the pump if the water heater's above the stove.
nick
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