furnace [RE-wrenches]

[Lawrence Elliott]

Hello Kurt!

I run into this very often in my area.

My first suggestion would be to completely ignore the ancient "forged
air and dust system"

In the last four installs I have registered from 640 watts as a low on a
1300 sg ft home and as high as 870 watts on a 2200 sg ft. That was the
actual load as recorded by a Brand meter at the furnace connection.
Untill I rewired the gas valve and thermostat to eliminate the phantom
load I had a 24 hr load of about 25 watts just to keep the furnace in a
ready state.

A little math gives you a real shock as to the power required to run
this "flaming beast".

Even at the low of 640 watts and a 30% duty cycle on a cold day your
looking at 5.12 kwh's/day.. And that's at a time when you have the least
power to spare.

Better to convince the owner to install a Toyotomi Lazer oil stove or a
Monitor oil stove.
They are about 90% efficient and on low setting they draw 33 watts.
Highest setting is 78 watts and idle load is 4 watts.

In many cases I have not been able to sell a PV system if the owner was
unwilling to switch from forced air to the Lazer etc.
The added PV's made the system way too expensive.

I am working now with one manufacture of modular homes and seeing if we
cannot install a product called Warmboard as the subfloor.
Warmboard uses 1/2' PEX tubing laid in grooves in the flooring panels. I
designed a proto system that was 1800 sg ft and the total power draw to
run the heating system less the fuel was only 80 watts. And that was on
AC. We could have saved about 20% if we used DC pumps. We calculated the
duty cycle at less than 20% at the 10 degreee outside temp rating.

Warmboard has a .025 aluminum sheet bonded to the wood so the heat is
evenly distributed to every square foot.

The heating of these modular homes using PV power for the blowers etc is
a real "achilles heal" of the industry.

Hope this helps
Larry Elliott




> Greetings all,
>
> I just got an off-grid job that is a new, manufacturered home.  It was
> delivered to the site completely wired and with most of the
> (inefficient) appliances and systems installed.  The home is all set
up
> for a forced air furnace (ducts installed) although the furnace has
not
> been purchased yet.
>
> I usually avoid such situations and have only done one off-grid house
> with a forced air furnace.
>
> I appreciate any recommendations on (somewhat) efficient furnaces with
a
> (fairly) small phantom load.  It's a 2,000sf (main level) home with
full
> basement and an SW will be the inverter.
>

>
>
>

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