Hi guys, I've been running under the radar for awhile. This is only because I wanted to fine tune this project before I posted anything.
The higher cost of anthracite coal and the lower cost of natural gas had me thinking long and hard about how to get the most out of a gas converted solid fuel furnace. I did much research on the subject of gas converted coal furnaces from years past and came to the conclusion that an efficent unit could be built using some of yesterdays and todays heating technology, making a hybrid warm air and hot water furnace.
The Clayton furnace I used was modified by installing a two inch steel pipe burner with a 24" flame and a Charles Hones Gas Burner Plain Air Mixer.
This link is broken, either the page no longer exists or there is some other issue like a typo.
I used a RobertShaw Thermostat Gas Valve with oven probe to set the stove temperature and RobertShaw gas valve for a wall thermostat. The furnace was then lined with fire bricks and angle iron to support the bricks into a complex long flue gas path within the stove in order to give more residence time of the gas in the stove. The fire bricks heat between 600 and 850 degrees, radiating to give a very constant even heat to the outside steel.
I wanted to recover as much heat as possible before it went up the flue, so a 15' custom copper 1 1/4" tube heat exchanger was installed above the burner and below the fire bricks. The natural gas flame heats this copper pipe heat exchanger and provides approxamately 45,000 Btuh, from the calculations of heat content, into my 40 gallon D.S.Machine wood boiler, which gravity heats the 50 gallon gas hot water heater and the 14" X 18" water to air heat exchanger in the air stream. I did have two Taco pumps installed at first, but the pumps made the water travel too fast to absorb much heat. I removed the pumps and went strait gravity flow with extremely significant increased heat absorbsion and recovery into the hot water side of the system.
For added house comfort, a homemade humidfier was built using a stainless steel pan, brass float valve, and copper float ball connected to a 1/4" water line. This was one of the best additions that I ever did to increase the comfort level of the house and doing it at a lower heating temperature.
The air stream is set up intially for gravity warm air flow up to 125 degrees where two 12" inline duct fans are installed in the supply trunk lines controlled with a fan switch. Once the jacket air temperature reaches 175 degrees, then the return forced air blower kicks on by another fan switch doubling the air flow through the duct system.
The system is a series set up. This is where the central cold air return goes into the blowers, through a water to air heat exchanger, passed a conventional 90+ gas furnace tube heat exchanger, through the air conditioning coil, then into the Clayton, passed by the humidifier, through the main trunk, then split into to trunks with inline duct fans, finally to the register vents.
There was a lot of calculations done for burner size, heat surface area, water heat content transfer and storage, desired flue exit temperatures, etc. This forum and old heating conversion furnace books helped greatly. This has been a long project.
Now that it is running, it is the my favorite attempt with system design to date. The hand fired bituminous coal was dirty and either too hot or cold. Stoker modifcation of the Clayton proved very ineffiecent for the surface area and needs electricity to function, plus I didn't like the every once and a while hopper coal gas smell. Hand fired Anthracite is awesome, but the much increased cost now is considerably higher than natural gas. Natural gas is so much easier, no tending, ash removal, or coal storage. Now that I have an even heating warm air and hot water system all in one which doesn't really require electricity, but operates a little more effiecently using electric blowers, I'm spoiled and wished that I did this years ago. I would have went natural gas gravity warm air and hot water at the very begining. I've learned a lot over the years and paid a lot learning along the way.
Hope you guys like it.
By the way, this also cooks pizza, baked potatoes, hot dogs, hoagies, and other great foods! Yes this is a great cook oven too!