Heat pumps for hot-water radiator systems

The question I asked during the webinar was not very clear.  We have a water based heating system with radiators and a boiler fueled by gas.  We also have an air-sourced A/C system with small tubes running throughout the house (a UNICO, high velocity system) without the hanging of mini-split systems in each room.  Is there any way of using an air sourced heating system to heat the hot water in our radiator based heating system (either through the existing boiler or directly to the hot water circulation system)?

Hi Alan, yes is the short answer, you can connect an air-sourced heat pump to a water radiator system. These are sometimes called hydronic systems. But the long answer is a big more nuanced. These type of air-sourced heat-pump to hot-water systems are made by Jaga, Daiken and Spacepak and other manufacturers. I have never used one so I have no particular recommendations. The hot water in a boiler-driven radiator system is typically at 140F. Air-sourced heat pumps have a hard time getting the output side (whether it is air or water) above about 110F. So your radiators will no longer have that piping-hot feel (which may be good or bad – I have nearly burnt myself on hot-water radiators before). This means that it will take longer to heat your house up from cold – like when you come home from a winter vacation. But, as long as the heat output is matched to your heating load your rooms will stay warm, it will just take longer to get warm compared to what you are used to.


Are you thinking of using the UNICO high-velocity system with a heat pump so it would heat in the winter as well as give you AC in summer? We have a similar system in our rental house and I would consider replacing it with a heat pump if such a system exists. Let me know if you find one.

2 Replies to “Heat pumps for hot-water radiator systems”

  1. Just want to be sure I understand this. We have a heating system with radiators in each room. The water is heated by a gas-driven furnace. We want to know if the gas furnace can be removed and replaced by a heat pump system that would heat the house in the winter and cool it in the summer. Also, how would the gas hot water heater for house fit (or not) with the heater pump. The house was built in 1978.

    1. Hi John, sorry it has taken me so long to reply, I was on vacation for 2 weeks.

      I do not recommend removing the gas-fired furnace if you add heat pumps. This is for two reasons, 1, I like having a back up heating system in case the heat pumps ever break down and 2, the gas-fired furnace can come on if every the heat pumps can’t keep you house warm enough in the depths of winter.

      Also, circulating cold water in the radiators to cool the house in summer (as opposed to circulating cool air) will likely lead to condensation on the floors or carpets. Some manufacturers of these heat pump driven radiator cooling systems state that cooling can be achieved but I am skeptical without personal experience.

      If you do not have any ductwork in the house today then you may be better off using mini-split heap pumps (which will heat and cool) in the rooms. I would still keep the gas furnace though as a back up.

      I hope this answers your questions.

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