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Homemade Wood Stove Hydronic Radiant Heat Setup

rbs12rbs12 Posts: 6Member
Let me start off by saying that I am not a contractor but a DIY homeowner/fabricator. I live in New England, needed an inexpensive way to heat my new living room so I built this heat exchanger for my wood stove last year to heat the radiant heat loop in my garage-turned living room. I couldn't find anything like this on the internet but used some information that I found on this site so figured I'd return the favor and put this out there for others to see.

The exchanger was soldered in place on the stove to make sure that it fit snug and is connected to the rest of the system in the basement via two unions. This way I can disconnect the whole system and move the wood stove if necessary. There is also a high point air vent at the top of the exchanger.

It's a big room (420 Sq/Ft) with 7" of concrete over the pex loop and a thick carpet and pad. I was nervous that this set up wouldn't be able to heat that much floor but it worked fantastic all winter long, keeping the room at 74 degrees.

Two relays control the whole system. There is a aquastat on the back of the stove that starts the circulator pump when the water directly around the stove is up to temp. The aquastat in the basement checks the overall temp of the heat loop. When that temp is at 120 degrees and the room calls for heat the relay open the 3-way directional valve which then loops the water to the floor until the water goes back down to 80 degrees at which point the loop closes and the cycle continues. There is a check valve just to the left of the "T" on the bottom pipe that stops the pump from pushing water back through the floor loop when the room is not calling for heat. The 3-way directional valves "off" state is set so that if I lose power the loop to the floor is always open. This should hopefully alleviate any over temp/over pressure issues when I lose power. There is also a pressure tank and release valve incase that happens. In the future I may upgrade to a back up battery for the circulator pump. When dealing with high temp water/steam one can never be too careful. The two on/off valves with drain allow me to isolate the heat exchanger, drain it and disconnect it without having to drain the entire system or make a mess of my floor when I do.

The reheat rate for the heat loop couldn't always keep up with the request for heat in the room so I would manually set the system to just loop the whole floor, then at times I had excess hot water available so I will be making a few upgrades/changes for the upcoming season. One will be to jacket the copper pipes with cement board under sheet metal to make it even more efficient. My plan is then to add a 3-4' length of radiant baseboard to the heat loop in the basement with some computer fans behind it. When the room is up to temp and I have excess hot water in the loop the fans will kick on to heat my basement. I'll update pics and info as I make them and hopefully it will not take me a year again. Overall I am very happy with the system and it cost me roughly $700 to build. I also did not notice any significant change in the amount of wood that I burned this year or a drastic change in my electric bill due to the circulator pump. Any questions or concerns feel free to comment.


  • rbs12rbs12 Posts: 6Member
    I forgot to add that the two led lights installed on the aquastat on the stove simply tell me what is going on in the basement without me having to go down there. One tells me the circulator pump is on and the other tells me that the floor is calling for heat.
  • Jamie HallJamie Hall Posts: 12,120Member
    Nice. Very nice. Especially that it is simple...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • ChrisJChrisJ Posts: 10,490Member
    edited August 2019
    What happens if the system leaks and runs out of water or if the pump dies and you have one hell of a fire going?

    I'm betting that stove can easily melt that solder.

    I'm asking because my boss built something similar and it really scared him one night when he was in bed and the pump died. Pex melted..... It was starved of water and in his words almost exploded. Whether or not that was true or even possible I don't know. But it really scared him and woke him up.

    He then built an outdoor wood boiler.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • JUGHNEJUGHNE Posts: 6,528Member
    Very inventive....looks good!
    I do see 30 PSI on the gauge, what is the pressure relief valve rated at?

    Things like this were attempted in the 1970's. Back then one thing I noticed was excessive creosote build up in the chimney
    do to lowered stack temp causing condensation of wood gases.

    Has your chimney build up changed from the past??
    As a 42 year volunteer fireman I have attended many chimney fires......just about always at the worst time of day.
    3 times we carried the still smoldering stove out of the house and put it in the yard......the wife would not let it back in. :'(

    In 1977 you could have been published in The Mother Earth News.....I still have the early copies. ;)
  • JellisJellis Posts: 184Member
    Cool unorthodox way to move heat around. I was happy to read you had a relief valve and took power outage precautions.
    I once did a service call for an "Engineer" who thought it wise to put a coil of copper in his fire place and pipe it to a radiator at the back of the room, no relief valve, no expansion tank.
    I wonder if a storage tank would be a good addition to your system?
  • rbs12rbs12 Posts: 6Member
    @ChrisJ I have also thought about all of this and this system does require some monitoring but for the reasonably low cost I'll be extra vigillant. There is a make-up valve attached to the system to account for any leaks that may occur and stop a "dry" situtation from happening. I check the water pressure gauge a couple times a week to check for changes. It is constantly at that 27-28 PSI range. If there was a leak the make-up valve only replaces 15 PSI so I'd see a difference. I've thought about adding another pressure gauge upstairs to save me the trip down but this also forces me to check the rest of the system as well. As far as the pump my house is only 1600 sq/ft so my stove is normally only turned up twice a day, in the morning when I get up and at night when I get home. The return line to the stove exchanger can be grabbed by hand and I always check it to make sure I can feel the water flowing through the pipe. If the pump were to quit between the pressure tank and pressure release valve I would hope they would control things until I got home and noticed.

    @JUGHNE The valve is rated at 30 PSI and the system runs just below that. In my research I did notice that people with the creosote issue mostly had that problem due to wrapping the pipe itself. I did update my chimney to a 6" insulated liner and extended it four additional feet at the beginning of last season as well. I did not notice any excessive build up this year.

    @Jellis I have also thought about getting some old H/W heater tanks from the local scrap yard to store the hot water but for now I'll just plug along with what I have. Maybe that will be my next upgrade.
  • GroundUpGroundUp Posts: 785Member
    That's pretty cool, very inventive. Something I'd like to mention is that there is no reason to be running 27-28 PSI especially with only a 30 PSI relief. The Extrol tanks are precharged to 12 PSI at the factory, did you pump the bladder up to 27 PSI to match your water pressure or what was the deciding factor on running such a high pressure when 12 was more than sufficient?
  • rbs12rbs12 Posts: 6Member
    @GroundUp I did not pump up the precharge, the system just "settled" to that PSI on its own. I never really thought too much about the running pressure. I guess I should put a gauge on the tank to check its precharge. Thanks.
  • GroundUpGroundUp Posts: 785Member
    @rbs12 it's not as simple as just checking the air pressure when there is 27 psi of water on the other side. You need to check the air pressure when the water pressure is at 0, then match the water pressure to what the air pressure is. There is absolutely no reason to run it above 12 psi, and the bladder will live a much longer life as well as the relief valve. Running that close to relief pressure will eventually create a leaker if it hasn't already
  • hot_rodhot_rod Posts: 12,564Member
    how will it circulate in a power outage? Maybe add a UPS to run the circulate in event of power out

    Any way to turn the fire off in the event of power out,

    Add ing a flue temperature gauge is a good way to monitor cold flue operation
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,875Member
    I would highly, highly recommend redundant circulators. Wire the second circulator off a second aquastat set to a higher temperature. This way if your first aquastat or circulator fails you have backup.

    I've burned wood for 100% heat and DHW for a few decades now. And trust me, time has a way of making things not work as planned or originally installed. Water in an enclosed vessel with an uncontrolled fire in very close proximity has a way of doing bad things if something fails. Power outages and circulation failures are your worst nightmare.

    A few years ago I had just finished my redundant dump zone (large unit heater in garage) for my gasification boiler. The first dump zone was fooling my radiant injection controller that the supply was 20 degrees cooler than it was making it ramp up radiant temps. This worked very well, until that very night when I finished my unit heater in the garage. Had a big power surge which blew up my radiant injection controller rendering it (ane my dump) useless. Well I learned that very night that it was worth my time to pipe up that big unit heater. Ran it for a couple of hours until that fire was out with no harm/no foul to the boiler.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • rbs12rbs12 Posts: 6Member
    @hot_rod I do plan on hooking up a UPS to the pump. My generator has this as one of its circuits so I won't have to put the fire out but if power goes out while I'm not home the UPS will cover me.

    @Solid_Fuel_Man Another good suggestion, redundancy can mitigage a lot of the risks with this type of system. You've got me making plans for modifications in my head as I type.

    Thanks for the input!
  • ChrisJChrisJ Posts: 10,490Member
    Is there a way to cut air to the fire in case of power outage?
    Such as feeding it via a blower and or using a spring loaded door that shuts if it loses power?

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • EYoderEYoder Posts: 58Member
    edited September 2019
    The wood boilers I install use a solenoid and flap, with a loss of power it drops shut.
  • rbs12rbs12 Posts: 6Member
    Appreciate the input from everyone and now looking for some more suggestions. I'm about the make my upgrades (close in the heat exhanger) and I'm not sure if cement board is the way to go. It looks like it has a mesh fabric intertwined in the outside of it which might melt that close to the stove. I was going to use hardibacker but it looks like that has too much fiber in it and isn't rated for heat applications. Any other suggestions other than regular cement board or steel?
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,875Member
    Steel would be your best bet. You are looking at some temperatures above 600F at times. I wouldn't use anything which will offgas, you could use aluminum as it's easy to work with.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SuperJSuperJ Posts: 574Member
    You'll kill that circulator prematurely by hanging the motor downwards. The shaft always needs to be horizontal.
  • hot_rodhot_rod Posts: 12,564Member
    If you ever build another a few suggestions, silver, high temperature solder. Ues return bends or bend the tube and eliminate a lot of solder joints.

    Good that it is outside the fire box :)

    I'd run the tube loops horizontally, you will trap air on top of every return bend should it ever flash or loose fill pressure and get air in the system.

    Some thoughts from building a handful of them over the years.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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