I installed a split mini heat pump in October 2009, putting the 'outside' unit in my crawl space where it can pick up heat from the ground through the crawl space floor.
It is a 12,000 - BTU per hour unit theoretically able to provide 288,000 BTU of energy per day - enough to heat my house in all but the coldest weather. The heat pump can provide 3.5 times as much energy as it uses - so for 3,400 BTU of electricity (1 kWh) I get 12,000 BTU or 8,600 'free' BTU of energy per hour.
It cost $700 to purchase on the web and I spent $90 for 3/4 hour of work by a pro to test and release the r410A fluid.
It is a little noisier than I like but still not annoying and I am insulating the crawl space ceiling to reduce compressor noise from the crawl space. If I did it again I might buy a unit with a 'rotary' compressor which would cost a little more but be quieter. I can hear the piston type compressor a little as it runs.
Also I need to build a plenum in the hall ceiling to suck cold air from the floor level of my house (through the space between my studs and drywall) up to the air intake at the top of the 'inside' unit of the heat pump. Now the heat output comes from below the unit, not far from where the air input is on the top of the unit. Consequently the machines turns on for a few minutes, then off again for a couple minutes, then on - all day. These changes should let the system run longer on and stay off longer - not 'cycling' so often.
So far I am getting plenty of heat in late November from this unit - drawing on 55F crawl space air rather than cold 30F at night outside air which would make the system operate with less efficiency.
I have learned that conventional heat pump systems for cold climates using water pumps and pipes in the ground can cost around $20,000 - so the saving for the split mini air-to air system $790 total (with me doing all the work but the final vacuum pumping, testing and fluid release) is huge!
Update. March 2010:
Having used the heat pump through one winter I can say it worked well, saving me money, time, effort and energy.
Every day that I use the heat pump I use more electricity that the corn stove requires, BUT NO CORN so I realize a savings per day of about $1 - and none of the work the corn stove requires.
Here are the numbers:
Average corn use: 2/3 bushel a day or 2/3 x $4 = $2.67 electricity used by corn stove about 12 kWh per day.
Heat Pump electricity use: about 26 kWh per day or 14 more than the corn stove x 12 cents per kWh = $1.68 a savings of 99 cents per day.
Over an entire heating season the heat pump will save the the cost (and trouble) of buying and handling 60 bushels of corn costing $4 x 60 = $240. The heat pump - running less as on warmer days will use about $140 more electricity (1,200 kWh) than the corn stove requires. Savings = $100 per year.
Adding homemade solar energy systems could cut or eliminate heat pump or corn stove use on sunny days. 300 or 400 square feet of solar collectors with heat storage might cut corn stove/ heat pump use in half.
I expect to build this system using soup cans (painted black), black TV dinner trays, scrap lumber, a few small fans (bought new) such as bathroom ventilation fans costing $15 each, scraps of vinyl siding, recycled window glass, and possibly 4 or 6 mill clear plastic costing a few cents per square foot.
So I am getting closer and closer to zero cost heating.
I have considered a metal box type wood burning stove on my main floor, and even begin building a rocket stove in my crawl space. There are plenty of sources of free wood around, dead ash and elms, pallets, etc. However I am worried about the of the fire safety of wood burning systems, especially where the flue pipes pass through ceilings, walls or roofs. Heat pump and corn stoves seem to me to be very safe. (A corn stove burns at a very low temperature compared to a wood stove - 600 vs. 1500 degrees. The flue pipe of a corn stove just isn't all that hot by the time the smoke passes through the heat exchanger - in fact there is usually very little smoke).
Then there is the issue of frequent attention required to keep the wood burner going, cutting wood, carrying wood, etc. The corn stove may run for a week almost without attention except to remove the clinker every 12 hours (a 2 minute job) and add 1 and 1/3 bushels of corn every other day.
A masonry fireplace heating system with heat absorbing thermal mass might be ideal for true zero cost heat, requiring only one hot burn for an hour or two a day to stores heat for 24 hours. But this type of system can cost at least $10,000 and requires a skilled mason which I am not. The thick mass of fireplace and chimney would - I think assure the safety of the system.
A rocket stove may be thought of as a kind of poor man's masonry fireplace. The homemade system I have begun in my crawl space is an experiment only and I worry I will burn down my house with it so I may never complete it. If I do I will report on it on this web site.
Update: February 23 2012:
I have attempted to go through this entire midle winter without using corn and relying entirely on my heat pump. I found that with constant running in cold outdoor weather the temperature in the crawl space fell below 40 degrees and the heat pump unit in the crawl space would gradually frost up and stop producing heat to the living space. To correct I had to stop running the heat pump until it thawed -taking about 12 to 24 hours, and then I it would produce heat again. I believe high humidy it my crawl space contributes to this problem (the water table is high on my lot and a sump pump keeps the crawl sapce dry, but water is near the surface of the crawl sapce and the vapor barrier on the crawl space floor is has openings). Also the perimeter of the crawl space is insulated, but cold be better insulated to keep the space warmer. The crawl space as a whole never falls below 39 degrees, but as it runs the heat pump itself, and the air going through it falls below 32 F and causes frost.
When the heat pump is not working I must go to 'pure' electricity to heat the house. This is expensive - about $10 a day vs about $7 a day with heat pump. The completion of my rocket stove should solve this problem, taking over heating the house when the outside tempearture gets too low or the heat pump freezes up.
Update March 14, 2012:
Well, I did it! I went through the winter using only the heat pump and occasional back up 'straight' electric heat. Now we are into warm early spring weather with 60 degree or more days and 40s or 50s at night - more than warm enough for the heat pump to keep the house comfortable. Any danger of heat pump freeze up is gone. One thing I do now, whenever the outside air temperature is above 45 degrees F - I open up the crawl space to outside air. The crawl space normally stays at about 40 degrees at this time - the temperature of groundwater (just below my crawl space) at this time. So warmer outside air raises the crawl space temperature the heat pump works with - and the heat pump works more efficiently. Also, outside air is dryer than crawl space air, mitigating the humidity that can build up in a closed crawl space.
To my knowledge, NOBODY has ever tried this before, (crawl space assisted heat pump) - except for one study and experiment by Oak Ridge National Laboratories (I think it was) about 30 years ago. Maybe I can get a patent or a grant or at least some recognition.
Update: February 23 2012:
I have attempted to go through this entire midle winter without using corn and relying entirely on my heat pump. I found that with constant running in cold outdoor weather the temperature in the crawl space fell below 40 degrees and the heat pump unit in the crawl space would gradually frost up and stop producing heat to the living space. To correct I had to stop running the heat pump until it thawed -taking about 12 to 24 hours, and then I it would produce heat again. I believe high humidy it my crawl space contributes to this problem (the water table is high on my lot and a sump pump keeps the crawl sapce dry, but water is near the surface of the crawl sapce and the vapor barrier on the crawl space floor is has openings). Also the perimeter of the crawl space is insulated, but cold be better insulated to keep the space warmer. The crawl space as a whole never falls below 39 degrees, but as it runs the heat pump itself, and the air going through it falls below 32 F and causes frost.
When the heat pump is not working I must go to 'pure' electricity to heat the house. This is expensive - about $10 a day vs about $7 a day with heat pump. The completion of my rocket stove should solve this problem, taking over heating the house when the outside tempearture gets too low or the heat pump freezes up.
Update March 14, 2012:
Well, I did it! I went through the winter using only the heat pump and occasional back up 'straight' electric heat. Now we are into warm early spring weather with 60 degree or more days and 40s or 50s at night - more than warm enough for the heat pump to keep the house comfortable. Any danger of heat pump freeze up is gone. One thing I do now, whenever the outside air temperature is above 45 degrees F - I open up the crawl space to outside air. The crawl space normally stays at about 40 degrees at this time - the temperature of groundwater (just below my crawl space) at this time. So warmer outside air raises the crawl space temperature the heat pump works with - and the heat pump works more efficiently. Also, outside air is dryer than crawl space air, mitigating the humidity that can build up in a closed crawl space.
To my knowledge, NOBODY has ever tried this before, (crawl space assisted heat pump) - except for one study and experiment by Oak Ridge National Laboratories (I think it was) about 30 years ago. Maybe I can get a patent or a grant or at least some recognition.
