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Radiant supplied with Passive Indirect tank and or odm electric heater?

Hello all you wise men of thermal comfort and heroes of heat loss havoc,

I originally posted this in Radiant Professionals but not sure if it goes there since I guess my question is more about what is supplying my radiant. I am installing a radiant floor in a room over my garage. The room is a split level lofted bedroom. It's 350sf with 16ft cathedral ceiling, windows on three sides, and no subfloor (worst design ever in regards to heating and cooling). The loft is on the 2nd floor. I'm installing radiant in the first floor level which is 190sf. The heat loss for the room is a little over 6k btu. I have a 80k btu non-condensing gas fired Utica boiler from 1968 (The same year my newly moved into house was built) heating about 40-50 feet of baseboard in the 2nd floor apt. above me which my mother-in-law occupies.. The rest of the house is unfortunately heated and cooled with a combi furnace. The furnace wasn't updated along with the new rooms and therefore is not sized correctly. I took the room off the furnace system and added 247 ft. of 1/2 pex 9" oc. with plates underneath the pine floor over the garage. There is no sub floor. I'm having the garage ceiling insulated with cellulose. Now, the total loop is going to be about 311 ft. I don't feel like injection mixing or 4 way valving my old boiler. I just want to do my thing and let it do its thing until i replace it with something else next summer or it dies a peaceful death Since my mother-in law keeps her apartment about 170 degrees in the winter I was wondering if I could take advantage of that by adding a plate heat exchanger and an indirect tank to supply my radiant floor.
-OR Installing an electric on demand heater closer to my floor. I was leaning toward a combination of both thinking it would save the most money. I live on L.I. where gas is less expensive than electric. I want my mother-in -laws boiler to heat my storage tank without making my indirect a zone for her boiler. I figured I would use the heat anytime she is heating her apt anyway and the odm heater would pick up the slack and combining it with the tank would help with its recovery time. Would a heat exchanger rob to many BTU's possibly causing the boiler to condense? Would I save more money one way over another?


  • ZmanZman Posts: 4,104Member
    It would be helpful to have something to help visualize this.
    If I am following you correctly, I think adding a 3 way smart valve and zone circulator piped directly to the existing boiler is the way to go. Any indirect setup adds a bunch of parts and logistics that just are not necessary.
    If you use a taco smart valve, you can get outdoor reset and boiler condensation protection all in one.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • HydroNiCKHydroNiCK Posts: 45Member
    edited September 2017
    Thanks for your reply. I guess what I was trying to say is I would like to pipe the indirect in parallel to act as an aquabooster or pre heater for my radiant floor without making it zone. I would have an on demand heater pick up the slack. I was worried that once the boiler runs through my indirect and my mother in laws baseboard the water temp would be too cool by the time it gets back to the boiler causing it to condense.I was thinking of doing it like this to save money on electric but I may be just splitting hairs depending on if the odm heater is electric or natural gas my savings might be minimal. I also need to cool the indirect's supply water down for my radiant floor. It may turn into more work than I wanted because I would be heating water in the indirect tank just to cool it down I'd some how have to mix the water in the tank with the cooler return from my radiant floor. I was thinking a zone valve before the tank. Open the valve whenever the boiler fires and have it close once the tank reaches a certain temp. Maybe like 10 degrees below the temp id need for my radiant floor. If the boiler doesnt fire and the water in the tank cools my on demand heater would bring it up to temp. OR I could just stop thinking and use an on demand heater only and forget about the whole thing. I could make a primary secondary loop but am worried that there are only 2 zones on the boiler and they would call for heat at the same time. Unless I pipe the odm water heater into that secondary loop hmm. But again I was thinking cheapest and least work but those two ways of thinking often don't work well together.

    This is the room: Walk about 4 feet up from the first floor

    Up the stairs is the lofted area which is the 2nd floor. The wall separates room from apt heated with baseboard. The Master bedroom is directly underneath the loft on the first floor. Below the first floor is the garage. I am installing radiant in the garage cieling/ this room's first floor. There is forced hot air in master bedroom and rest of the house. There is baseboard on the second floor on the other side of the common wall. Window to the front of me, on my right, and to my back. 16ft ceiling.

    opposite view window and 10ft cieling no subfloor

    tearing apart garage for radiant piping and insulation

    This is where all the magic happens...or maybe not. Its about 32 feet to the loop. I calculated 3.9' head. I may have to install small on demand heater closer to garage since the distance is a little long

    Welcome to the garage..Straight ahead the top of the knee wall is the basement cieling. On the other side of that wall is the master bedroom. If you look up you can see the loft room with no subfloor.

    So now you can see what i'm dealing with. That room gets no heat from the two forced air registers that were in there. Whoever designed this is an idiot. As you can see someone told the previous owner they could fix it by adding 15 feet of electric baseboard. So now if you think about it I have 4 different methods of heat in my house. Forced hot air,hydronic baseboard, electric baseboard, and soon to be radiant. I want to eventually get rid of the furnace and boiler and install a reverse cycle chiller(s) which I think would be perfect for my situation since that loft room needs AC now anyway.

  • ZmanZman Posts: 4,104Member
    Can you post a sketch of the boiler piping you are proposing.
    I don't see why you would not zone all of it in parallel including an indirect water heater.

    Why are you concerned with boiler condensation? What are your loads?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • HydroNiCKHydroNiCK Posts: 45Member
    I'm concerned with condensation because if I don't make my indirect a zone and just have a zone valve open every time there is a call for heat to the apt baseboard thereby passively heating the indirect tank I will be robbing heat that is headed to the upstairs apt baseboard. If the water is designed to come back 20 degrees cooler and if it is already coming back 20 degrees cooler my indirect tank stealing heat from the baseboard supply would make the return even cooler.
    I thought about piping it like this in order to save money on gas since the baseboards' call for heat pre-heats the indirect and if my tank temp drops because the baseboard hasn't called for heat the electric on demand heater will act as a back up bringing the tank up to temp. for my radiant floor. I could have the indirect call to the boiler when it needs to be heated but like I said my mother in law keeps her apt warm anyway. if i zoned it I would have to make her baseboards a priority over my floor. No? And number 2...that boiler is 50 years old. I wanted to mess with it as little as possible. Even If I take the temps right now and the differential is 5 degrees I don't really want to mess with it. If my thinking doesnt make sense on this let me know. My load is 6k BTU.
  • ZmanZman Posts: 4,104Member
    I can't get my head around what you have and where you are going.
    I would suggest ready Caleffi's Idronics series

    Sometimes it is really hard to fix an old cobbled system piece by piece and you just need a do over...
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • HydroNiCKHydroNiCK Posts: 45Member
    Thanks for your replies. I realized I was thinking about this way too much and splitting hairs. I'm going to take your advice and install a Taco i-series valve.
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