Jeff

I am looking at replacing a traditional fireplace with a wood stove insert that can be used in a hydronic floor system.

I looked over your article on the fireplace you installed in your home and have spoke to and web searched for wood stoves that circulate water for heated floors and find only the “long burners” for outside or commercial “furnaces”, nothing that would be appropriate for a great room/ranch application.  Can you point me toward manufacturers that have this type of product?

Thank you.

Mark J. Bechtel

Mark,

Jeff Yago

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Hi Jeff,

Mike:

Although most heating of buildings and homes before the advent of central air conditioning systems was hot water or steam radiators. Now things are changing again and many up-scale homes are starting to utilize hydronic heating due to the higher energy savings and comfort. Our 3 story solar home has a built-in masonry fireplace in our ground level (partly below grade) family room. This fireplace has a Hydro-Heater hydronic firebox which is “hollow” on all 3 sides and the bottom which allows water to flow around these areas then this water flows up into a heat exchanger containing 90 feet of boiler tubing. This heated water is then pumped into a air heat exchanger located in the discharge side of my central air handling unit, which circulates this heated air to every room of our home including all 3 floors. When we have a roaring fire in this fireplace, every room of our home stays at the same temperature and there are no cold spots.

I have also designed many systems like this for others only we piped the heated water to baseboard hot water radiation located in each room, and used motorized zone valves to allow each room wall thermostat to separately control the temperature of each room. Although most of the wood-forced boilers you will find advertised these days usually are the self-contained type that is located outside and piped into the home, there are still several manufacturers that offer “hydronic inserts” that look like a log holder that you place inside a standard fireplace. Many wood stove manufacturers offer an optional hot water coil feature, but these are usually intended to only heat a domestic hot water tank and not the entire house.

Yes, you can heat a radiant floor, but the problem is most radiant floor heating systems keep the water temperature in the lower 100 to 120 degree range, and most hydronic wood stoves can easily produce hot water in the higher 160 to 180 degree range which is much better suited for a baseboard radiation system. This means a radiant floor system will require a storage tank with one small pump circulating tank water through the hydronic fireplace to heat the tank, and a second small pump to circulate heated tank water at a different flow rate through the radiant floor piping. Remember, boiler water or water passing through hot water radiators and radiant floor piping usually will include additives to reduce sludge and rust, and you cannot mix with your domestic hot water system (sinks and baths), so if you want to also heat your domestic hot water tank, you will need a separate coil in this storage tank for that piping.

You are on the right track, but remember, these are classified as a “boiler” and if you don’t include the proper pressure and temperature safety relief valves in your piping, these things can blow up and do some real damage. Also, manufactured hydronic stoves are made from “boiler grade” steel which is much stronger with no flaws or weak spots. This may be why there are not as many manufacturers these days and why I do not agree with your “beer keg” idea!

Good luck,

Jeff Yago

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Jeff:

Randy:

You have two problems. First, pump sizing and pump flow rates must be calculated for the specific application, and it varies depending on the flow rate, water temperature, floor thickness, spacing between each heat pipe in the floor, pressure drop of the pipe being used, and if you will have any additives like antifreeze. In other words, check with the supplier of the tubing as most provide easy sizing tables that will help you determine the pressure drop and pumping head. I will suggest that many of the systems we have been involved with had pumps between 1/20 and 1/12 HP for most applications. Keep in mind an AC water pump will not have brushes inside and a DC water pump will have carbon brushes that will need to be replaced about every 2 years. Most people now use AC pumps and an inverter.

Your larger problem is the water temperature and water heater. Many are designed to heat cold ground water entering around 50 to 60 degrees and always have cold water entering at the bottom and the hot water out the top of the tank. Some tank water heaters and almost all instant type hot water heaters will fail if piped into a re-circulating hot water loop as the return water temperature stays above 90 degrees. Again, you need to check with a supplier in your area who supplies radiant heating equipment before making a mistake you cannot fix without a jack hammer.

Radiant floor heating systems are my favorite type of heating as it is simple in operation. However, like most things that look simple in operation, they require far more design effort than may appear.

Jeff Yago

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