March 5 , 2000
System - Backup
The backup system will incorporate some form of a wood fired stove and a propane or electric boiler. The reason for this is twofold: (1) the sun doesn't always shine and (2) if we are away for any extended period, we need to keep the house minimally warm to prevent any freezing from occurring.
Wood is the logical choice for our secondary heat source. There's plenty of it (approximately 50 acres of woods) and it's a form of renewable energy. (Some of the RE purists might disagree with this, but it does not use fossil fuels and it is renewable.) With a combination of solar and wood, our heating bills should be next to nil.
There are plenty of methods for heating with wood: outdoor wood burning boilers, indoor wood burning boilers, combination gas/wood burning boilers, forced-air combination gas/wood burning furnaces, wood burning stoves, wood burning stoves with hot water tubing and masonry stoves. And I'm sure I've missed a few. I have pretty much researched them all to death. Here's my take on some of the possibilities that I have considered:
Wood Burning Furnaces
Aqua-Fyre, AquaTherm, Central Boiler, Heatmor, Taylor, and Wood Master are manufacturers of oudoor wood burning stoves. These systems vary in price from $2,600 to over $6,000. They all use cast iron or stainless steel to enclose a firebox around a water jacket. The water is pumped underground to the house to heat domestic hot water, radiant floor systems or retrofitted forced air systems. Most have prorated warranties of no more than 10 years. The longevity seems a bit questionable as the water and excessive heat take their toll on the water jacket. Plus, they are overkill for the heating needs of our particular house.
A rather unique outdoor heat system is the HAHSA II. The HAHSA is more of a concept than it is a product. HAHSA can be purchased in a kit form or just the plans. The HAHSA uses water coils to carry the heat from the unit to the house and uses sand to store heat around the fire chamber. To do this, a cinder block house needs to be built (8' x 10'). Then the firebox is built out of firebrick. Next comes a cage made out of copper pipe and PVC pipe for domestic water. To finish things off, tons and tons of sand are poured into the structure and insulated along the wall edges. This would surely heat the house and would last longer than a conventional wood boiler. The downside to the HAHSA is the pipe cage that is used - way too many fittings to potentially leak and the amount of time, money and labor used to build the structure. (Using some form of tubing around the firebox would be a better solution than the cage they use, but I'm not sure if it would be as efficient.) Producing up to 90,000 BTU's per hour, this would be overkill for our heating needs and a lot of work to build this furnace.
Alpha American, Charmaster, HS-Tarm and a few others use a combination of wood and gas/oil to heat either radiant floor or forced air heating systems. These systems vary in price from $3,500 to over $7,000. Most of these systems do have better warranties from 10 to 20 years. The forced air systems use more power to move heat than the radiant floor methods, although the manufacturers say the furnaces will still gravity heat the house with no power. The advantages to these systems are combination of fuels (backup fuel source built-in), somewhat better longevity and less BTU's escaping out into the cold. The disadvantages are that your bringing the fire into the house. Insurance will be higher and you'll have to bring in the wood to fuel the fire.
Most of the wood burning stoves on the market today are built for beauty as well as functionality Prices can range greatly. Since my intent is to heat the house with the use of radiant floor heating, my interests have been focussed on only those stoves that include hot water options. This can be done by retrofitting a wood stove with a stainless steel coil or purchasing a stove that has this option factory installed. Thermo Control is a wood stove that can provide up to 80,000 BTU/hr and has options for factory installed coils. Although it is rather ugly looking, it is quite functional and practical.
If you are looking for a stove that can give you a more constant, long lasting heat, a masonry stove does the trick. Because masonry stoves are built using stone or brick, they have a lot of thermal mass. Stainless steel coils can also be built into the unit to provide hot water. The advantages are that they fully burn the wood and provide a more even heat than a wood stove. They also have longevity -- they should last you a lifetime. The downsides to a masonry stove is the amount of space that it occupies and the cost. Masonry Stove Builders and Tempcast offer firebrick insert kits. The inserts cost $3,500 to $5,000. And that's just the insert! Even if you did everything yourself, without a mason's labor, material costs would still be quite expensive. (With a mason's labor, I was given quotes of $10,000 to $15,000 for a complete stove!)
As you can see, there are quite a few options available here. So what will be our design? I hope to wrap things up in our next journal entry.