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Saturday, February 07, 2015

Heating with wood

The second house I owned, we had built.  I decided to have a free-standing wood stove installed, and even had the builder design a special alcove for it, so that the stove wouldn't take a bite out of the living room.  It also kept the hot surfaces well away from people.

That stove was magnificent, easily heating a 2700 sq.ft. house out on the cold, windy high desert.  It saved us a ton of money when the price of natural gas spiked to over $10.00 MMBTU, back in the early 2000s.  When everyone was suffering with awful heating bills, we heated the house all winter for very little money.  We were able to get a cord of hot-burning, low-ash hardwood (Almond) for about $180/cord, which lasted most of the winter.  That's what a lot of people were paying each month heating with natural gas.

This is the model we had.  Our model had the gold-plate door, but had black legs.

The next house we lived in had a real brick masonry fireplace, which was fitted with natural gas and artificial logs.  It was useless for home heating.  I enjoyed heating with wood and also enjoyed not being mugged by the natural gas utility company.  Unfortunately in that house I could not install a free-standing stove, and so we had to make do with a wood-burning fireplace insert.    It didn't put out nearly the amount of heat that the wood stove did.  To help compensate, it was fitted with a fan which blew air from underneath, around the firebox, and out into the room. The fan was quite noisy, and the wood-burning insert used a lot more wood to make a lot less heat.

This unit is similar to the one we installed.  The fan mounts down at floor level, under the lip.

A wood-burning insert fan.  These come with a variable-speed control knob (right side), so you can decide how much howling you are willing to put up with to get a little heat out of the fireplace.  On a positive note, it has a thermal switch (center) to shut the fan off after the fire goes out.

The house we are currently in uses a heat pump for HVAC.  I am not really happy with the heat pump, because it's about 20% short on capacity for this size house.  It's a 5 ton unit and it really should be 6 to 6.5 tons.  We don't use it very much for cooling, because it usually gets cool enough overnight to get by with window fans.  In the winter months though, we keep the house pretty cool, and we still have enormous electric bills.  I would like to fix that.

The house also has a zero-clearance gas (propane) fireplace that you turn on by using a wall switch. It looks cheap, even though it's surrounded by very nice masonry and a beautiful mantle.  For heating though, it's pretty much useless.

Below, not my installation, but the fireplace insert looks just like that...  and yes it also has a spot for a howling fan.

I don't have space for a free-standing wood stove in this house, because it would take a big chunk out of the living room.  Wood stoves require quite a bit of clearance to prevent radiant heat from starting fires.  And yet... I like heating with wood.  There is a lot of it here.  Furthermore we know a few people who wouldn't mind having their property cleaned up and would give us the wood.

I have been investigating the alternatives, and thought perhaps this is what I should consider:  A wood furnace.

A wood furnace works by putting a great deal of wood inside the firebox, and allowing an electronics package to control the burn rate.  The firebox is surrounded by a water jacket, and the fire heats the water, which circulates from the firebox through underground tubes to a heat exchanger in your furnace.  The fan in your home's furnace blows air across the heat exchanger and warms the air and distributes it throughout your house.   The cooler water returns to the firebox to be re-heated.

Here's the overall diagram that shows how the installation works.

Image showing the supply and return tubing, insulation and protective sheath.

The wood furnace water is above the temperature your hot water heater puts out, so you can install a heat exchanger on it as well, saving even more electricity.

Below, a diagram showing how the wood furnace interfaces with the hot water heater.

Interestingly, they make wood furnaces with dual pumps, so that you can heat multiple buildings (or a garage) with a single furnace.  You simply add a second loop and another heat exchanger for your other building.  I'm really interested in this arrangement because wood stoves and wood-burning fireplace inserts have some drawbacks that are eliminated.

If you have ever heated with wood, you know about the mess.  The wood you bring into the house always has leaves, dirt, bark, and bugs on it.  Sorry, I don't inspect each log I bring into the house for cleanliness - not if am hauling in 5-10 per day.  Then there is ash.  You have to clean out the stove, and it's pretty messy.  Half of the stuff gets airborne (especially if you are doing a hot clean-out and the ashes are still glowing).  The other half of the ash gets on the hearth and has to be vacuumed afterwards.  I caught a vacuum cleaner on fire once and ruined it, when I sucked up a glowing ember :)

Then there is the issue of cleaning the flue annually to prevent chimney fires - followed by the hazard of having a months-long fire in your living space.  That increases the potential for carbon monoxide poisoning.  I actually kinda like the idea of keeping the fire, toxic gases, ash and bugs (dead or otherwise) outside of the house.

Perhaps the best part of wood heating is that you avoid using fossil fuel, while switching to fuel that is local.  With wood heating, you can be much more independent from electricity prices, fossil fuel production and distribution prices, from taxes on fossil fuel, and from international events that could have a huge impact on fossil fuel delivery/prices.

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