[Greenbuilding] heating water with wood stove - heat transfer/efficiency calculations?

Reuben Deumling 9watts at gmail.com
Wed Nov 9 14:19:08 PST 2011

Thanks, Gary.
The situation in question involves a stove that might be on two hours per
day. That is the main reason for inquiring--to see if it is reasonable to
assume an adequate amount of heat would be transferred to the water.
As for a coil on the stovepipe--it would be on the outside of the pipe: no
draft implications from that.

On Wed, Nov 9, 2011 at 12:21 PM, Gary BIs <gary at builditsolar.com> wrote:

> Hi,
> There are some articles here: http://www.builditsolar.com/**
> Projects/BioFuel/biofuels.htm#**FireboxCoils<http://www.builditsolar.com/Projects/BioFuel/biofuels.htm#FireboxCoils>
> The articles give some hints at heat output -- like this external coil one:
> "How much hot water will the exchanger produce? Well, during a typical
> seven-hour cycle we would load 55 to 60 pounds of wood into the Atlanta
> Catalytic, which would boost the 42-gallon tank's contents to just short of
> 140° F. This eight-pound-per-hour burn rate is probably somewhat higher
> than most folks use, so the volume of hot water that you might get from a
> similar unit could be slightly less. Of course, if you maintain a strong
> burn all day long, the total over a 24-hour period should still be more
> than 100 gallons per day of plenty-hot water. And even if you often operate
> your stove in a "closed down" condition, the system will significantly
> reduce your utility bills."
> Read more: http://www.motherearthnews.**com/do-it-yourself/woodstove-**
> water-heating.aspx?page=3#**ixzz1dF0uYXN2<http://www.motherearthnews.com/do-it-yourself/woodstove-water-heating.aspx?page=3#ixzz1dF0uYXN2>
> The outfit than makes the inside of box coils gives some hints at how much
> water each model will heat up.
> I think that anything coupled to the outside of the stove or the outside
> of the chimney is going to have low efficiency, but if the wood stove is on
> a lot anyway, maybe that OK.
> Some people don't like the idea of coils on chimneys as it may effect
> draft to the point of making problems.
> Gary
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