Heat Pumps for Hydronic Baseboard Heat?

PilotPat24 · June 2022

Hi Guys,

Do they currently make Heat Pumps to supply hot water to Hydronic Baseboard?

Thanks,

Pat

Hot_water_fan · June 2022

Yes - with caveats. The Idronics journals cover this really well, I’d start there.

iced98lx · June 2022

Hi Pat!

I'm not an expert, and agree with checking out some articles in Hydronic Journals but last time I searched for Air to Water heat pump there were a few companies doing it with a 2 phase heat pump, and then there were also a few companies doing water -> water (AKA GeoThermal) heat pumps for it.

A quick google suggests there may be more available now, but here are some links to get you started:

https://www.greenbuildingadvisor.com/article/air-to-water-heat-pump-retrofit

https://www.daikin.com/products/ac/lineup/heat_pump

https://www.arcticheatpumps.com/

Most were focused on in-floor due to the lower temp requirements but a few got as high as 150 IIRC which is what I run my baseboards at.

Hope that helps!

fentonc · June 2022

I've been doing a lot of reading about this as well. I agree with @Hot_water_fan - there is a great Idronics issue about this. There are several air-to-water heat pumps (theoretically) available, although finding someone to install/service them will depend on location. Arctic, Aermec, Spacepak, and Enertech make them, amongst others. There are 'cold-climate' as well as inverter-driven models available, but as others mentioned, they usually top out at like 130-135F as the maximum water temperature. Several of them also have integrated electric boilers, and can supplement as needed.

For retrofitting a house with hot water baseboard, it's really important to actually understand the heating requirements for your house. 180F seems to have been the standard assumed supply water temperature for many hydronic systems, but many systems are also grossly oversized. Baseboards will still put out heat at lower temperatures, but the output is reduced as the delta between baseboard temp and room temp lowers. There are also 'high output' baseboards (with bigger/more fins), panel radiators and fan coil units that could all be installed to replace/supplement existing baseboards if more output at lower temps were needed. After doing a lot of measuring, my house has enough baseboard that it could probably handle 110F-120F water just fine.

PilotPat24 · June 2022

Thanks for all of the great information. I first need to calculate the heat loss for my house and determine how much baseboard I have currently. I'll be back with more information!

Hot_water_fan · June 2022

Good to hear Pat! Try using this for the heat loss: https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

Dave H_2 · June 2022

Yes, do your heat loss and get it as accurate as you can. When designing with am Air to Water heat pump, the math is going to be of the upmost importance. Alot of the software has so much fudge it, find the areas where the extra is and minimize it.

Then as for designing for low temp heat emitters, we recently covered this in a Taco After Dark webinar. Here is the link

jumper · June 2022

Various sorts of baseboard. Fintube needs relatively high temperature compared to cast iron or steel panels. The first is convection while other ones radiate somewhat.

Hot_water_fan · June 2022

All baseboards (and radiators) are a mix of radiant and a lot of convection? There’s no reason a heavier baseboard radiates more is there if the surface area is the same? All baseboards can work with low temperature water, it’s just if you have enough BTUs to meet the load.

EBEBRATT-Ed · January 2023

I seriously doubt that heat pumps are viable for baseboard heating unless you fill the entire house with baseboard. Anyone who thinks they can get 130 deg out of a heat pump (don't forget all it is is a reverse air conditioner) you head pressure will be out of sight. Yes you may be able to run it at that high temp for a while. How long do you think the compressor will last. I would give it 5 years at best. Think about what your asking the machine to do

WMno57 · January 2023

Don't forget your outdoor A2WHP will need Glycol. If you don't want Glycol running throughout your house, you now need to buy a heat exchanger for your basement. You do have a basement don't you?
If your OK with Glycol running through your aged baseboards, you still have the problem of less ability to transfer heat. If your baseboards are marginal at 130F 100%H20, what happens at 130f 30%Glycol?
Glycol is for cars and garages. It will eventually make a mess in your home. Why don't the Heat Pump Cheerleaders ever mention this?
"I hate Glycol" famous words of a wise hydronics consultant, known to The Wall.

yellowdog · January 2023

spacepak's solstice system a2whp does not require any anti freeze.

WMno57 · January 2023

Show us some some split A2WHP systems. Who makes them? SpacePak is a monobloc correct? Monoblocs require glycol, correct? How about a link to an on-line vendor like www.supplyhouse.com?

Hot_water_fan · January 2023

Spacepak makes both. Nordic makes a split one as well.

WMno57 · January 2023

Educate me. Is this is a Monobloc that requires glycol?

https://www.spacepak.com/Themes/SpacePakTheme/images/resource/SpacePakHouse714.png

GGross · January 2023

I believe the spacepak does require glycol, though there may be a unit I am unfamiliar with that does not.

from the manual for the solstice extreme

full manual here
https://www.literature.mestek.com/dms/SpacePak/ILAHP Manual (ILHP2-0722).pdf

WMno57 · January 2023

Apologies for the blacked out picture. Maybe all the electric cars and heat pumps have caused a rolling blackout. I'll fire up some Traditional Fuels and attempt to post a better picture.

Hot_water_fan · January 2023

Educate me. Is this is a Monobloc that requires glycol?

Spacepak makes both. Hope that clears it up!

WMno57 · January 2023

Peakedtoosoon said:
"Don't forget your outdoor A2WHP will need Glycol"
Not if you install a split system, where the heated water is contained within the home.

yellowdog said:
spacepak's solstice system a2whp does not require any anti freeze.

https://www.literature.mestek.com/dms/SpacePak/SIS2-0421_2.pdf

"If unit is operating in a cooling capacity then the
water system must contain a mixture of inhibited
glycol and water with thermal protection sufficient
for the coldest expected temperature for the
installation. The inhibitor level can degrade over
time, and may need to be adjusted periodically.
The inhibitor is essential to prevent the glycol from
accelerating corrosion of metal components in the
system. The glycol and inhibitor levels must be
checked regularly (no less than once annually).
The minimum allowable concentration of glycol is
10% by volume in all installations."

MikeAmann · January 2023

EBEBRATT-Ed said:
I seriously doubt that heat pumps are viable for baseboard heating unless you fill the entire house with baseboard. Anyone who thinks they can get 130 deg out of a heat pump (don't forget all it is is a reverse air conditioner) you head pressure will be out of sight. Yes you may be able to run it at that high temp for a while. How long do you think the compressor will last. I would give it 5 years at best. Think about what your asking the machine to do.

Peakedtoosoon said:
Ideally, you should aim for a supply temp of 113F, with a Delta T of 9F (104F Return), when sizing radiant heat emitters for use, with an ATWHP. Hydronic Baseboard BTU outputs, are based on much higher supply and return temperatures (180/160), but you can get low temperature, fin-tube baseboards.

If you have the standard baseboards, then you'd have to either reduce the home heat loss by about 50%, or double the amount of baseboards you have, in each room. Some ATWHP models run higher than 130F, so you could run the heat pump at a higher flow temperature. However, you'll pay for it with reduced SCOP or HSPF, as you call it in the US.

You may also need a supplemental heat source, depending on outdoor winter temperatures.

Would a good intermediate step towards eventually going to a HPWH be to replace the standard hi-temp fin-tube baseboards with new low temperature, fin-tube baseboards? I can do the plumbing myself. Would this be worth it, since I could then lower the supply temp of the current boiler down to 150F?
House is a ranch - 1 heated floor - back loop is 35.66 ft of fin-tube, front loop is 38.83 feet.

EBEBRATT-Ed · January 2023

What is low temp baseboard?? Baseboard is baseboard either CI or fin tube it will work at low temp the question is do you have enough wall space that will take enough baseboard to do the job. Most homes do not

hot_rod · January 2023

WMno57 said:

Apologies for the blacked out picture. Maybe all the electric cars and heat pumps have caused a rolling blackout. I'll fire up some Traditional Fuels and attempt to post a better picture.

Or the bitcoin mining farms sucking electricity
One transaction consumes as much energy as the average home uses in a month

Follow the money, one farm in NC kept running while the surround homes were dropped off. They cut a sweetheart deal with the power company

hot_rod · January 2023

Here is an example of a low temperature fin tube

Both Jaga and Runtal have some mini fan boosted fin tube assemblies made specifically for radiant temperatures
120 SWT seems to be a sweet spot for A2WHPs

https://smithsep.com/wp-content/uploads/Heating-Edge-2-Literature-2.pdf

MikeAmann · January 2023

@hot_rod
Thank you. That's what I was referring to .... fin-tube baseboards designed to work with the lower temperatures of a heat pump (120-150F). Install now and lower the temp of the conventional HW boiler, and then be all set down the road for a heat pump or mod-con boiler.

Would it be worth doing?

psb75 · January 2023

Runtal has a the most attractive options for lower temperature, true-radiant "baseboard." Heights of 6", 9", 12" in many different lengths with multiple plumbing-connection options. All connections are female threaded 1/2" NPT.

lkstdl · January 2023

WMno57 said:

Peakedtoosoon said:
"Don't forget your outdoor A2WHP will need Glycol"
Not if you install a split system, where the heated water is contained within the home.

yellowdog said:
spacepak's solstice system a2whp does not require any anti freeze.
https://www.literature.mestek.com/dms/SpacePak/SIS2-0421_2.pdf

"If unit is operating in a cooling capacity then the
water system must contain a mixture of inhibited
glycol and water with thermal protection sufficient
for the coldest expected temperature for the
installation. The inhibitor level can degrade over
time, and may need to be adjusted periodically.
The inhibitor is essential to prevent the glycol from
accelerating corrosion of metal components in the
system. The glycol and inhibitor levels must be
checked regularly (no less than once annually).
The minimum allowable concentration of glycol is
10% by volume in all installations."

Interesting find WMno57. Note that is for cooling mode, not heating. Typical chilled water supply temps are 4C-7C (39F-45F), somewhat above the freezing point. Anybody know is it typical for commercial chiller systems to use glycol? Does the Spacepak have poor control of LWT so they want extra safety margin?

EBEBRATT-Ed · January 2023

Commercial chillers use glycol if the chiller or any of it's piping is outdoors or in an unheated building where the temp can drop below 32 degrees. Typically run 30% glycol

lkstdl · January 2023

Would a good intermediate step towards eventually going to a HPWH be to replace the standard hi-temp fin-tube baseboards with new low temperature, fin-tube baseboards? I can do the plumbing myself. Would this be worth it, since I could then lower the supply temp of the current boiler down to 150F? House is a ranch - 1 heated floor - back loop is 35.66 ft of fin-tube, front loop is 38.83 feet.

Do you have easy access to the underside of the floor? Personally I'd be inclined to add staple-up radiant to the floor rather than removing and replacing existing baseboard.

JohnNY · February 2023

WMno57 said:

"I hate Glycol" famous words of a wise hydronics consultant, known to The Wall.

You forgot remarkably kind and handsome as well.

Patchogue Phil_2 · October 16

https://forum.heatinghelp.com/discussion/188454/heat-pumps-for-hydronic-baseboard-heat

Hi

Did you ever go forward with an install?

RobertJordan · October 21

Siegenthaler is an advocate for AWHP. He has written a number of columns for Plumbing & mechanical and Plumbing and Mechanical Engineer. Propane is allowed as a refrigerant in Europe which enables AWHP to produce 175 degree water.

delcrossv · October 22

https://forum.heatinghelp.com/discussion/comment/1735110#Comment_1735110

I'd like to see their outputs at 100 degree SWT. Then I could run it with radiant ceilings and no mixing valves.

DCContrarian · October 22

https://forum.heatinghelp.com/discussion/comment/1815578#Comment_1815578

Output is going to be directly proportional to the temperature difference between the surface and the room.

The 6" Runtal is rated at 600 BTU/hr/ft with an "average water temperature" of 180F. That means an aquastat high setting of 190F and low of 170F. A system like that will typically be designed for 20F drop so water is returning at 160F, the average temp in the radiator is 170F, or 100F above room temperature.

Typically with heat pumps you aim for lower drops because you're starting at lower temps. Let's assume 100F SWT and 90F return temp. So an average of 95F, or 25F above room temperature.

The output at 25F above room temperature is going to be 25% of the output at 100F above room temperature — 150 BTU/hr/ft.

delcrossv · October 22

@DCContrarian excellent, thanks! Makes for a large panel, but worth it to, in my case, run condensing all the time.

DCContrarian · October 22

https://forum.heatinghelp.com/discussion/comment/1815603#Comment_1815603

They also make 9" and 12" high baseboard that are 770 and 930 BTU/hr/ft nominally.

hot_rod · October 22

a wall can be turned into a supersized panel radiator , ideal for HP temperatures also

DCContrarian · October 22

Siegenthaler gives the formula that heat flow from a wall or ceiling is equal to 0.71 times the difference between air temperature and water temperature (he doesn't provide a source). So if your water is leaving at 100F and returning at 90F, you get an average water temp of 95F, with room temp of 70F that's a 25F delta and 17.75 BTU/hr/sf.

So if you did the whole wall it would be close to the 150 BTU/hr/ft of the baseboard.