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Does the Air to Water Heat Pump Work with Hot Water Baseboards or Radiators?

By Nordic

February 01, 2016

Heat Pump Installation

air to water heat pump hot water baseboards radiators
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A common question I’m asked by homeowners is whether or not a Nordic air to water heat pump will work with their current HVAC system. If their home has existing radiant in-floor heat installed, the answer is usually yes, an air to water heat pump can act as a direct replacement to their current system.

But if your home has hot water baseboards or radiators, the answer is not a simple one, and depends on the output temperature of your current heating system. Let’s look at the important factors to consider when deciding whether to replace your current system with an air to water heat pump.

How Output Temperatures Vary from System to System

First of all, let’s establish a definition for a residential hydronic heating system: A system that uses hot water to heat your home. The water is first heated by a geothermal heat pumpg, an air to water heat pump, or a boiler that is powered by either wood, oil, natural gas, or electricity. The heated water is circulated through a heat distribution system (radiant in-floor piping, hot water baseboards, or radiators) before returning to your heat pump or boiler to be reheated.

Depending on what system you have in place, the output temperature of the hot water that heats your home will vary. If you have an oil-fired boiler feeding hot water baseboards or radiators, your output temperature is probably around 180°F (82°C). This higher output temperature means you’ll need less surface area to radiate enough heat to keep your home warm.

In contrast, other heat distribution systems like radiant in-floor heating require much lower output temperatures and radiate their heat over a much larger surface area (a whole floor vs. a small radiator). Our air to water heat pump is built for those lower temperatures, and has a maximum output temperature of 120°F (48°C).

So, can you use a low-temperature air to water heat pump to heat a home with a heat distribution system that is designed for higher temperatures?

The answer is: Maybe.

How to Test if 120°F Water Will Heat Your Home

The truth is, it may work, it may not. There’s an easy way to determine whether or not 120°F water is hot enough to keep your home warm.

Simply turn down your heating system’s output temperature to 120°F. This will circulate water that is only 120°F to your home’s baseboards or radiators. If you do this for a winter and your heating system maintains your desired room temperature (the setpoint), then you know that it will work. If the lower temperature water isn’t enough to keep your home warm, you’ll know because your home won’t reach its desired setpoint or may have trouble maintaining the setpoint on the coldest days of the year.

Using this method, you can determine whether or not our low-temperature air to water heat pump will work with your high-temperature heat distribution system.

Generally, the air to water heat pump will work with radiators, but is less reliable with hot water baseboards, but again, it depends on each individual home. Our product engineer Dan Rheault offers this insight:

“I have a heat pump paired with hot water baseboards and they work, but our home is not at the desired set point all of the time.”
Dan Rheault, Product Engineer

Again, our recommendation is to test your home’s heating system at the lower temperature for one heating season, and then you can determine if you can switch to an air to water heat pump.

Interested in learning more about the Nordic ATW Series? Download our FREE Ebook:

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Photo Credit: jasonpier

Comments

  1. Reply

    Lionel scott

    February 28, 2016

    My home on 51 havelock St Amherst ns is heated by a condensing gas boiler controlled by outdoor reset . Today February 28 2016 the temperature outside is 41f and the house is 68f emitters are lots of baseboard . Boiler water temp 81f . Gj used from March 19/14 to March 19 /15 148.21 cost 3613.44$ .the house was Is converted to 4 apt in 1996 .

    • Jordann Brown

      February 29, 2016

      Hi Lionel,
      To determine if an ATW Series heat pump is right for your home, contact a local installer. You can find an installer near you by using our find a dealer tool: http://www.nordicghp.com/find-a-dealer/

    • Tom Antrim

      October 08, 2016

      I have a Geo Spring water heater heat pump and my home is 1000 sq ft well insulated new windows with recent concrete slab siding. I alway wondered why I couldn’t use it to run through water radiators.

    • Jordann Brown

      October 11, 2016

      Hi Tom,
      There are a few reasons. First and foremost, the GeoSpring unit uses heat from inside the home to heat your hot water (with a temperature range of 35° F to 120° F), so there needs to be a primary heat source providing that heat like a furnace or boiler, otherwise the unit will just operate in full electric mode which is not efficient.

      Second, the GeoSpring unit is meant to heat domestic hot water for a home, and would not have enough capacity to heat a 1,000 square foot home.

  2. Reply

    craig melanson

    April 30, 2017

    hi..would this be a good system to replace an oil firred boiler? currently it costs about $3000 a yr in oil to heat the house…so looking for alternate system

    thank you

    • Jordann Brown

      May 01, 2017

      Hi Craig,
      This would be an excellent substitute for an oil fired boiler. The only thing you’ll need to check, which is outlined in the blog post, is the output temperature of the boiler, and the lowest possible operating temperature for your heat distribution system. As long as your distribution system can comfortably heat your home at 120F temperatures, the ATW Series is a good option.

  3. Reply

    George Shears

    October 20, 2018

    I am purchasing a bi-level with both in-floor radiant and hot water baseboard heating. Would it be energy efficient to replace the oil furnace/boiler, with a air to water heat pump system, as well as adding a standard split heat pump (one serving the top floor and one serving the bottom floor)?
    An implementation like this would provide consistent heat in the winter, as well as the ability to provide faux A/C in the summer.
    Thanks,
    George

    • Jordann Brown

      October 22, 2018

      Hi George,
      The ATW Series would work well with your radiant in-floor system, and it could provide chilled water for fan-coil based air conditioning on the upper floors, eliminating the need for mini-splits. The area I would be concerned about is any rooms that are serviced solely by hot water baseboard heating. Often this type of heat distribution system needs hotter water than the ATW Series can provide. Please email info@nordicghp.com to discuss your setup further.

  4. Reply

    Nicholas P Laskovski

    August 17, 2019

    What if we used the Nordic system as a primary at 120F paired with an oil fired backup at 180F?

    Our new (to us) home has a combination of radiant, hot water panel heaters (runtals), and fin style baseboard hot water. Currently all heated by (2) oil fired boilers, including DHW. I’d like to add a Nordic ATW system into the mix even if at minimum it would just boost water temperatures requiring the oil burner to burn significantly less.

    We’re in central VT where the need for a backup is required based On temperatures dipping below zero and sustaining during winter months. However, I’d guess that 80-90% of runtime the temperature range would be suitable for the Nordic ATW system, significantly reducing our demand for oil. Paired with our planned solar system, this would be a large benefit.

    Efficiency Vermont rebates are favorable for the Nordic system curently and offset the equipment price substantially enough to reduce risk.

    • Jordann Brown

      August 27, 2019

      Hi Nicholas,
      Thanks for your interested in the ATW Series! You could do this system, but the challenge would be to ensure that the 180F hot water never makes it back to the heat pump, since those high hot water temperatures would cause safety shutdowns. A local HVAC company should be able to design a system that prevents this, and our technical support team can offer guidance as well. An alternative would be to retrofit the portion of the home with high-temperature hot water baseboards to accept low-temp radiant panels, turning the entire system into a low-temperature system. This would allow you to eliminate the oil boiler completely, and use our buffer tank with electric elements as your sole backup heat source.

  5. Reply

    Robert Theriault

    August 29, 2019

    Presently have traditional hot water baseboard heating system. Would like to replace baseboard radiation with low temp rad. I know output of present rad in btu’s,did cal at installation time. with btu on low temp rad, length of new rad is easy to find. Eventually install air to water heat pump. realistic?

    • Jordann Brown

      August 30, 2019

      Hi Robert,
      Yes, this is very realistic and is done frequently, as long as the new low temp rads are rated for the air to water heat pump’s output (105F – 120F), this is an excellent strategy.

  6. Reply

    John Henderson

    June 29, 2021

    Our house is a well insulated ’79 built split entry with oil fired hot water baseboard in three zones. Furnace is cold start so there is no reserve volume of water. Set point now is 170F. I will perform the 120F trial next heating season but need to know if the Nordicghp system will adapt to it.

    • Jordann Brown

      June 29, 2021

      Hi John,

      If your system can get you through a winter heating system at 120F, then the air to water heat pump should work for your application. You’ll need to add a buffer tank to your setup, which will serve as a holding tank for heated water and also your backup heating system.

  7. Reply

    AnonJohn

    August 30, 2021

    One ought to be careful about this experiment if you have a cast iron boiler. If the boiler has not been plumbed to protect against low return temperatures (e.g. injector control) temps below 130 deg can cause corrosion to the cast iron and / or burners. This is potentially dangerous. Indeed, this concern probably shouldn’t be done with such boilers. Alas!

    see, e.g. https://www.weil-mclain.com/sites/default/files/field-file/cga-series-1-manual_1.pdf

    pg. 20

    • Jordann Brown

      September 01, 2021

      Thanks for the information, John!

  8. Reply

    Hunter Smith

    September 18, 2021

    I just looked at my boiler (a traditional natural gas boiler from 2001). I saw where it measures the output temperature, but didn’t see anything at all that let me control the output temperature. Do most boilers have that feature?

    • Dan Rheault

      April 08, 2022

      Hi, sorry, Jordann departed and no one checked the blog for a long time!

      I’m not a boiler expert, but as far as I know they would need to have a temperature setpoint so they know when to come on. This could be a mechanical or digital device, mounted in or separately from the boiler.

  9. Reply

    Lance McLaughlin

    March 06, 2022

    I have a traditional baseboard hot water heating system powered by oil. However,I have central air for A/C with air ducts throughout my home. Can the heat pump system integrate with my my air ducts to provide me with heat & a/c ?
    Thanks

    • Dan Rheault

      April 08, 2022

      Hi, sorry, Jordann departed and no one checked the blog for a long time!

      NORDIC does make triple function heat pumps for hydronic heating and ducted air heating/cooling, the TF and ATF series. But they don’t have the high temperature water heating capability that you would need for hydronic baseboard heat. So in this case you could look at a reversing WH-series (water source) heat pump to heat water to as high as 160°F for your baseboards, and also do cooling via a ducted hydronic fan coil. That’s assuming you have a ground loop or open loop supply temperature of 45°F or more available all winter.

  10. Reply

    Charles

    July 25, 2022

    We have a simple baseboard heater setup with a side arm, the gas boiler heats the water for the side arm and heats the baseboard water directly, pretty sure the temp gauge shuts off at 160F or so when heating. We have no aircon. Unit is burnmann boiler from 1992 – sidearm is new. So you are saying there is no current simple heat pump solution for this setup? I think a lot of US household used forced air but surly there is a market for hot water baseboard heating? Sounds like it’s a technology limitation? I would have to make my radiators bigger right? Like the ones we see in Europe?

    • Dan Rheault

      July 25, 2022

      Hi, currently air to water heat pumps can’t heat water to 160°F, although upcoming Nordic models may have that capability (we may introduce such a model next year). To use lower temp water, you are correct in that you could upgrade your radiators to have more surface area, so would be able to radiate enough heat into your space using the lower water temperature (105-120°F).

  11. Reply

    Jesse

    October 28, 2022

    Hi Dan, we have a 100-yr-old house in Boston Massachusetts, using the original hot water radiators with an oil boiler. I’ve done some calculations and believe we could heat the house with 120-degree water in the existing radiators as you described above. However, the radiator water is old, rusty and gunky, and I’ve heard that this isn’t good for heat pumps. Could we use a heat exchanger tank to isolate the existing radiator loop from the heat pump loop, thereby keeping the heat pump loop clean? Thanks –Jesse

    • Dan Rheault

      October 28, 2022

      Hi, you could do that, but you would lose some temperature between the heat pump and radiators due to the additional heat exchanger. You might be better of to thoroughly flush each radiator during the retrofit. I have seen some pretty clogged up with rust and gunk, and flushing them would be difficult but perhaps worth it to get a higher flow rate through them and therefore better performance.

  12. Reply

    Jesse

    October 29, 2022

    OK, thanks Dan. How clean does the water need to be in order not ruin the heat pump coils? If we just did a big flush of the entire radiator system from the boiler output pipe in the basement, might that be good enough?

  13. Reply

    DOUG

    February 09, 2023

    HI Here in Sackville NS.
    ..currently air to water heat pumps can’t heat water to 160°F, although upcoming Nordic models may have that capability (we may introduce such a model next year).
    My Veissmann furnace runs app 140–160 in winter
    HWH baseboard……
    So is this new model a true AIR to baseboard heater and would be the installed price??

    • Dan Rheault

      February 09, 2023

      Hi, we have not got very far in coding/testing that new design, unfortunately. We may still release it at some time in the future, but no date.

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