Radiant baseboard and tankless?
criddle
| Posted in Energy, Heating & Insulation on
I was wondering if someone had radiant baseboard heating, is it kosher to use a tankless water heater instead of a boiler? Seems like in theory it should work.
Replies
Well in "theory" any heat source that can heat water will heat radiant baseboard.
What it comes down to is efficiency, life expectancy, & cost of the heat source.
A water heater tankless or tank is nothing more than a boiler that is approved for potable water applications.
“A universal peace, it is to be feared, is in the catalogue of events, which will never exist but in the imaginations of visionary philosophers, or in the breasts of benevolent enthusiasts.” —James Madison
Well the efficiency part seems like it couldn't be better, so the only thing might be the cost of the tankless. Is there anything physical that would preclude using tankless?
Well you don't want it too big for the system--- ie too many btu's which will cause "short cycling" & greatly reduce the life expectancy of the unit.
We do "tankless" boilers all the time, except for floor radiant systems mainly cause of the lower temps that radiant floors run on. We have done tankless, but usually incorporate a holding tank for tempering purposes.“A universal peace, it is to be feared, is in the catalogue of events, which will never exist but in the imaginations of visionary philosophers, or in the breasts of benevolent enthusiasts.” —James Madison
Thanks! The short cycling makes sense and explains why I haven't seen this touted at all.
Thanks! The short cycling makes sense and explains why I haven't seen this touted at all.
A modulating tankless won't short cycle because it adjusts the btu output to match the desired water temp going out. The other advantage to a computerized modulating water heater (or modulating boiler) is the output temp is adjustable, often eliminating the need for a temperature mixing valve.
For such things we've used the Takagi TK-Jr. for years and it may not be the cadilac, but it works well. It's Takagi's smallest modulating heater and is rated for radiant heat as well as domestic hot water. At $600 ($300 after the tax credit) it's hard to find a better deal.
If someone knows of a better deal in a modulating tankless boiler I'd love to know about it.
Good heating.
Beer was created so carpenters wouldn't rule the world.
that's not exactly true bill. Try running your water heater up to 180. I think you'll see a difference.That said there are times and places for water heaters and tankless water heaters for sure. But they are not necessarily equivalent to boilers in all systems, and they are definitely not equivalent to mod/con boilers in most systems.-------------------------------------
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OK I was over generalizing, Hey my WH's do run at temps that high, but I doubt you will ever see one in a house.“A universal peace, it is to be feared, is in the catalogue of events, which will never exist but in the imaginations of visionary philosophers, or in the breasts of benevolent enthusiasts.” —James Madison
We have a system with a combo tankless boiler that does both baseboard heating and DHW. It replaced an ancient cast-iron monstrosity and a separate 50-gal water heater. Over the past 3 years our gas usage is down about 15% with the new setup.
On the DHW loop we installed a 30-gal electric heater as a buffer tank. It's not powered normally but we can flip a breaker and connect it if we ever need to. The boiler can supply 3.5 gallons per minute and with the buffer tank that is enough to handle one shower running constantly plus an intermittent load like a washer or dishwasher.
Tankless heaters designed only for DHW lack the controls needed for baseboard heating (temperature setpoint, outdoor reset, loop freeze protection, etc.) and I'd think that might be a show stopper if you try to use one for that purpose.
I am curious...what brand is this dual purpose tankless unit?
It's the Luna 310i made by Baxi.
I have a tankless water heater that I hated as a water heater, used for comfort heating in my garage, part of which is heated by finned tube convectors (i.e. radiant baseboard), the bulk of which is heated with 95 degree water inside of imbedded tubes in the slab. I run the water through the baseboards first with entering water at about 120 degrees.
The problem with using a domestic water heater (DWH) with hot water/radiant baseboards could be capacity. Typically, though not always, baseboard and radiators are selected for their required output based on 180 or 200 degree water being supplied. Most DWH's have high limit controls that prevent the temperature from exceeding 140 degrees, or so. So the only potential problem would be getting enough heat out of the baseboards at the lower water temperatures. Mine put out about half of what they would at "design" temperature water of 180 degrees. OTH, for small, low temperature water heating applications, like infloor heat in a garage or small addition/renovation, the tankless water heater works well.