Hello fellow home performance folks!

I am looking to heat a single room with a hydronic coil that I can tie to an existing, domestic, hot water heater.

Does anyone know of a small, hydronic, baseboard unit with a built-in recirculation pump and thermostat that I could use to heat a single room? A built-in fan would be pretty awesome too? Am I asking for too much? 

I haven't done the load calcs yet, but I'm guessing around 5000 btuh.

I have also looked at direct vent gas heaters like the Rinnai https://www.rinnai.us/direct-vent-wall-furnace/product/ex08c_rhfe-2.... I've also looked mini splits, and hotel room style through-the-wall heat pumps. 

But I would prefer a hydronic solution due to the adjustability of water temperatures by changing the rate of hot water flow. I don't want to over heat the room.

I install a fair number of First Co VHBQ hydronic air handlers for central forced air heating systems. Being able to fine tune the delivered BTU's is fantastic for comfort and even temperatures.  But I need something smaller for a 150 sf bathroom.

I seem to run across this situation with some regularity - that one room that the homeowner wants to control separately, or that cannot be added on to the existing central system.

Any suggestions would be much appreciated.


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Bachi .  Placing electric strip heat under the subfloor is probably sure to fail .  I do not believe they can get hot enough to provide anything at all through that type of resistance .  Good luck .

Electric strip heat can get expensive as well. But I think that Eric was referencing hydronic "strip" heat. A buddy of mine just installed a hydronic, underfloor heating system. His only complaint is that it takes many hours to meet set point from a cold start.

  As a hydronic professional for more than 30 years I can safely say I never heard of hydronic "Strip heat "  .  Maybe Eric can clarify ?

So far, the Beacon Morris K series hydronic kick space heaters seem like the best fit. What I like about them is:

  • Small size
  • Versatile: adapts into a kickspace, under floor, or in a stud bay
  • Different sizes available: 1800 - 9000 btuh
  • Reasonable price: $200
  • Built-in aquastat that turns on the fan when it senses 120 degree water
  • Built-in fan: watt draw is 30.7. I'm not seeing any specs for noise level.
  • Adjustable heat output via water flow and temperature

Would need to add the following at some expense:

  • 115V power
  • Line voltage thermostat
  • Recirculation pump: Taco seems to be a well regarded brand
  • Timer to deal with Legionella safety issues

Of course, you never know the full story on new equipment until you install it and live with it for a while.

  For just a bit more than 200.00 you could purchase Joist Trak plates or similar , 5 sheets (32 sf) of rigid foam , and tubing and drywall to cover .  Save 30.7 watts x 3200 hours and have a noiseless , more comfortable radiant ceiling .  This also could run varying water temps and flows .

  How would you vary the temp and flow with the kickspace heater ?

Can you link to product reviews of a ceiling install? Scared of anything w/o a proven track record..

Bob .  There is millions of sq ft of radiant ceiling in commercial space all over the globe .  Walls and ceilings are often overlooked or even laughed at since most think heat rises as opposed to the reality that hot air rises .  What are the odds that the top of the sun is always facing Earth ?   Ceilings may be the very best surface to use as a radiant heat emitter since you're very likely never gonna see some woman's oriental wool rug on the ceiling or furniture .  You get the benefit of every square inch of out put .  Since we all hot goes to cold you can be assured that all the heat energy goes to the coldest surfaces to build MRT and eliminate those body heat sucking exterior walls and windows .  Heating and cooling surfaces has been done naturally for Eons , since the dawn of time , not accepting that it happens and not using it is just plain , well , counter intuitive to our goal of using less energy and doing maximum work .





Are you going to use this for a 150sf bathroom? If so 5MBTU seems quit high.

Wouldn't it be much simpler to just install a small electric wall heater. that can be controlled easier and only when needed?

Why go to that much trouble? The installation cost is low as well as the operating cost.

The  load is actually closer to 3000 btuh. The bathroom has five exterior sides. It also has 60 sf of glass. The electric heater is the easiest option - and is currently being used. This solution is costing about $300 annually in electric bills. With some air sealing and insulation I figure that I can get the heating cost down to less than $50/yr using natural gas. Closer to $200/yr using electric. Its worth finding a gas solution if I can keep parts and labor under $2000. Otherwise electric heat will probably win the day. Thats my current thoughts on the matter so far.

3,000BTU is MAXIMUM load @ design conditions. How many hours are less than design? Our entire house with a 44k furnace only uses $150/yr in gas (doesn't include the additional $400/yr in fixed meter fees), $50/yr for a bathroom doesn’t sound right.

Hey Bob, Sounds like you have a tight house. My heating bills are about the same with a 18k water furnace.

I don't claim to be a master at these calculations, so check my numbers. Maybe I missed something. I copied from my Excel spreadsheet so I hope the formatting is okay.

Assembly R value U Value SF BTUH
Walls 12 0.083 249 20.75
Windows 1.1 0.909 57 51.82
Floor 20 0.050 144 7.2
Ceiling 20 0.050 144 7.2
Total BTUH       86.97

Q  =  U x A x HDD x 24
HDD for San Fran 2600
Q (Annual BTU's) 5309611
Annual Kbtu 5310
Annual Kw 1557
Annual Therms 53.1
$/Kw 0.20
Annual Kw Cost $311
$/Therm $1.17
Annual  Fuel cost $62

I'd run the bathroom heater on a timer. Homeowner will want a "boost" of heat in the morning/showers. Exact temp isn't an issue, they just want the heater "wide open" for 15-30 minutes.


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