The Walden Effect: Farming, simple living, permaculture, and invention.

How to install an exterior wood furnace

Moving the trailerThe cheapest house you'll ever find is an old trailer.  Ours is 10 feet by 50 feet and we got it for free, though it cost us $2,000 to haul it onto our land.  (That figure included a good bit of driveway building then dragging the trailer through the floodplain with a dozer.)  We recommend the old, free trailer approach to anyone who wants to live simply on the land. 

With our housing now taken care of for $200 per year in real estate taxes, it was time to decide on a method of heat.  The problem with trailers is that they are fire traps --- a wood stove (which is often the most economical and also one of the best environmental options) was out of the question. 

So, for winter #1 we heated with electric space heaters, keeping the room temperature hovering a bit above freezing and still spending up to $126 per month on our electric bill.  We couldn't help also being concerned about the environmental cost of using excessive electricity derived from coal.  That winter was a bust.

Exterior wood furnaceOne solution would have been to insulate the trailer, but we're striving for cheap here, and trailers are expensive to retrofit.  Instead, we chose to install an exterior wood furnace.  There are a bunch of options out there, most of which involve water flowing around a stove and being pumped into your house, but we didn't have running water at the time and were going for easy anyway, so we chose an air-flow model.  Mark's mom found the furnace you see here for a bit over $200 on ebay.

Installing the furnace was simple --- Mark dug out a bit of earth and put down cinderblocks, then set the stove on top.  An insulated air hose went from the top of the stove into the trailer, and a similar hose went from the ductwork already in place under the trailer back to the stove.  (Mark had to rig a homemade version of the insulated air hose this year out of
Hot air outletinsulation and flashing since Huckleberry used the hose as a bed all summer and ripped it up.)  A fan, which came with the stove, keeps the air circulating --- hot air comes into the house and cool air comes out.  For winter #2, our electric bill went down to $60 to $70 per month.  That paid for the stove in the first year --- and we were toasty warm!

A couple more notes on installation are in order.  When we first put in the stove, we tried to blow the hot air through the barely insulated, under-house ductwork and up through vents all through the trailer.  That didn't work.  You want to use the tendencies of hot and cold air in your favor --- blow all of the hot air into the house as quickly as possible, then suck cold air at floor level back to the stove. 

Roof with stove pipeIt's not necessary to build anything around your exterior wood furnace, but our standard of living went up when Mark put in a porch-type roof over it.  It gave us a dry place to store a couple of days' worth of wood and also means that we don't have to stand in the rain when we feed the stove.

The wood is easy to come by (though it keeps Mark in shape during the winter sawing it into lengths and both of us in shape splitting it.)  The powerline cut has so much deadwood in it that we expect it'll last us for another four years at least.  We're thrilled with our heat setup and see it as yet one more step in our path to total independence.

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.

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How do you keep the smoke out of the trailer? It looks like some of it would go up the duct into the trailer and smoke things up. I see the other pipe out of the back of the wood burner, but still... Is there a separate chamber for heat to go in and out of that's closed off from the burning chamber?

How long does a load of wood burn during the winter? Can you load up before bed and stay toasty all night?

Great solution!

Comment by Everett Mon Feb 23 16:27:51 2009

The furnace is a little more complex than a simple wood stove. It has
an air pocket outside the main part of the stove which heats up due to
the fire but doesn't interact with the fire and thus doesn't get smoky.
We use a fan to push air through the pocket and into the trailer, and then pull air out of the trailer to go back into the pocket. Thus ---
no smoke!

Mark usually gets up once during the night to poke at the fire, though
I've noticed that as he gets better at loading the wood in at night, that isn't as necessary. On the nights he sleeps through, there are usually enough coals left to get a good fire going pretty quickly. It
helps to burn denser woods like walnut (or oak) at night so that the wood lasts longer.

The house temperature does drop at night, but we figure as long as it's above 50 F, that's warm enough for sleeping!

Comment by anna Mon Feb 23 18:46:36 2009

This is one of the best diy'er sites ive seen from normal down to earth people ive come acrossed yet! Come here looking for chicken care(since I am a first timer with chickens),about 8:30pm and now its 2:00 am. Every time I think ive got what I came for I see another subject that catches my interest. Your now on my favorites list:). Most of your ideas are so simple and practicle,and within reason for low income households.Cant get enough of your plight to be self efficiant.Im jealous, you have each other to work as a team. It really helps to have your spouse seeing things the same as you.. going to seriously check more into out side furnaces. I will be ordering 1 or 2 of your chicken waterers wihtin the next month, Im tired of the slimy hay filled floor waterers. Anyways just thought i'd say what i was thinking. Thanks to both of yas.

Comment by Dav Sun Jul 12 02:10:27 2009
It's great to meet you, Dav! I'm glad our DIY posts hit the mark --- we're always hoping that other people can learn from our mistakes. We look forward to hearing more about your adventures.
Comment by anna Sun Jul 12 08:48:08 2009
What does your insurance company say about the stove so close to the trailer?
Comment by Anonymous Wed Nov 11 12:36:31 2009

We got our trailer for free, and I figure it's worth a few hundred dollars at the most, so we don't have it insured....

The furnace seems to be a safe distance away from the trailer, though. We never have sparks flying. At the worst, a charred log might drop out the furnace door onto bare dirt, but that goes out quickly and is far from the trailer.

Comment by anna Wed Nov 11 17:05:50 2009
Okay, so heat from the enclosed fire is circulated into mobile home and existing ducts bring colder air back, but how are smoke and fumes from the fire exhausted? I know I'm missing something here but I'm Thanks, PZ.
Comment by PAUL ZENTZ Sun Feb 16 14:51:19 2014
Paul --- There's a chimney that comes out the back of the exterior wood furnace, where there's no sleeve for air flow. The smoke goes up that chimney just like in a normal wood stove.
Comment by anna Sun Feb 16 16:49:14 2014
I worked on a similar setup a few years ago, the only difference was that, I rigged up the furnace to a radiator, the radiator had water circulating through it which supplied heat to the rest of the house. this was the safest option I could think of at the time and worked well for quite some time. By the way, there was a large fan on the radiator that blew hot air around the living space, both the water and the fan worked on the same pump, and the pump was operated by the rising heat from the furnace, talk about maximum efficiency;-).
Comment by Eric Blaise Fri May 29 13:56:31 2015
How much wood do you use per day and per season to heat the trailer?
Comment by Bree Thu Aug 2 17:31:29 2018

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