Auxiliary woodburning furnace

[rick_morrell]

We recently purchased an older farm house (~90 years). It has an updated furnace, but I would like to offset my propane bill because it's a brick home with no exterior wall insulation. Does anyone have any experience with outdoor woodburning furnaces?


Thanks,
Rick

[Pat]

Rick, I confess that I didn't "do the math" but you might find sealing up the drafts and adding insulation to be a better investment. If you do a heat loss analysis and look at the cost-benefit of insulation, caulking/sealing/weather stripping, and updated windows you might find a better investment opportunity than adding an external wood furnace to the house as it is.

There are web sites with heat loss calculaltors yo can find with Google. A sample of the Governments offerings...

http://www.eere.energy.gov/consumerinfo/energy_savers/

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[rick_morrell]

Pat:

Thanks for the information! That website is very informative.

I'm also going to be building a 30' x 50' outbuilding for a garage and workshop. Another reason I was considering the outdoor furnace was because I could heat the workshop as well as augment the furnace. Given the value of a good insulation strategy for the home, it looks like I'll be heating the outbuilding separately. Do you have any suggestions for a separate furnace?

Thanks for the advice!


Rick

[Pat]

Rick, You are certainly welcome for the advice. If it is worth more to you than you paid ($0) then it is a bargain! Think of it as a delayed tax rebate. I was once the Energy Conservation Officer of SUBASE San Diego and the taxpayers paid for me to get smart on a lot of topics so it is only fair that I share with a taxpayer.

My garage/shop/tractor/implement shed that is connected to our new house is a 48x57 open span engineered steel truss bld. The prefab trusses, I beams, "C" chanel etc are a custom "kit" from Miracle Steel in Minnesota. It is a 48x36 bld with 12 ft wall height and 12:12 pitch gable roof. The tractor and implement shed portion is a 4:12 shed roof section (21x48) along one side with connecting doors. The 36x48 part is subdivided into two 24x36 rooms. One has three overhead doors in the gable end (3 car garage) and is vaulted to the peak as we didn't need more floor space. The other half of the bld is finished off as a 1 1/2 story and is connected to the house by two sets of doors, in series, for an airlock (keep out fumes and noise.)

The story and a half is the shop. The ground floor is MINE and has 10 ft ceilings. The attic has a flat ceiling section at 11+ and 12:12 pitch ceilings down to the 5'6" level then walls and is 1/2 mine. The original design for the house and shops included 3 ground sourced heat pumps and propane backup in the form of decorative parlor stoves (direct vent gas logs.)

As Lenox came out with a new (almost 2 years ago, now) air to air heat pump that is rated at 19 SEER, we changed the design to include two of those and only one ground sourced water to water heat pump for the hydronic heat (various slab, ceiling, and wall installations.)

The shops (unstairs and down) share a small 19 SEER heat pump with a Lenox propane furnace as the air handler. An outside thermometer decides whether to run the heat pump or fire the furnace. The switch over point is about 35 F now but can be set to a different temp if the relative economy of propane vs electricity changes. I have a small generator that can run the air handler so the propane furnace is a back up for when the grid goes down (we get ice storms every so often that take out the power.)

As an after thought I added on the sun room to that unit although it is not big enough to do all three spaces at the same time. They are three separate zones with in-duct electronically controlled dampers so since we can't be in three places at once the little unit will only need to handle at most two rooms at the same time.

The Lenox 19 SEER unit is at least as economical here as a ground sourced unit! We calculated a 20 year breakeven on the ground sourced unit vs the Lenox air to air. If the ground sourced unit lasts over 20 years, I'm marginaly ahead.

At one time I considered burning wood in a remoted furnace (wife's cousin has one in Arkansas) but after analyzing the situation I decided against it. I'm sure it is appropriate for a lot of folks but it just isn't for us. The version that heats water and supplies it to the structure was my favorite technology had we gone with wood. There are multifuel units available that will let you use oil or gas for backup.

I frequently get asked for advice on whether to go for gas or electric and my answer is insulation and a tight house with engineered ventilation (not dependent on accidental/incidental drafts.) I would like my house to be so tight that it popped your ears when you slam an outside door. It won't be but I can dream. An ERV or HRV will supply your fresh air needs with good economy during heating and air conditioning seasons. I have two ducts to my range hood, exhaust and intake so most of what I exhaust is ambient air from outside not conditioned air from inside the house (I like powerful range hoods.)

Insulate the slab and foundation edges of your to-be-heated outbuilding. My HVAC contractor supplied bubble wrap with aluminum coating on one side to reflect heat to go under the slabs where he did in-floor hydronics as well as my shop. I used 2 in rigid foam (R-11) under the basement floor and on the outside of the basement walls. Look up the Government DoE guidelines for your climate zone and insulate AT LEAST AS MUCH as they recommend, more is better. The insulation will pay for itself over and over in energy cost savings as the years roll by. Don't bet that energy costs will go down or that cold fusion will be common place in a couple years.

Hope some of this was of interest...

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[rbhollabaugh]

Rick,
I would also agree that making your house more energy efficient is the best bang for the buck. I owned an old Victorian house for 10 years and the best thing I did was rebuild the original windows (with proper seals) and get blown in fiberglass put in the exterior walls. Cut the heating bill by 75% and made the house much more comfortable to live in.

Rich in NJ