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Community and Q&A

Retrofitting Boiler System with Heat Pump

bill02888 | Posted in Energy Efficiency and Durability on

I have a home in central Massachusetts with an existing oil-fired boiler. 8 zones. It frequently short-cycles. Looking to switch to a heat pump to free ourselves from CO2 generation. Standard size Slant/fin baseboards. I’m thinking air-to-water, possibly using CO2 a a refrigerant so that the existing baseboards can be used as-is.

Keeping the existing baseboards would allow me to use my existing oil-fired boiler the next time we experience a long-duration power outage; I have a Sonnen battery, plus other portable batteries, which can run the entire oil-based heating system for multiple days.

Home is timberframe so it’s more difficult to run new plumbing than in a conventional home. Walls are SIPs. Current Slant/fin plumbing runs between posts and SIPs at the corners of the house.

Hoping to use the Massachusetts rebates to do this.

Seems as though most CO2-based heat pumps are still in Europe, and/or are mostly sized for commercial, although I did see that one company has a few hundred residential units installed in the USA.

I also saw and did read this article:

Air-to-Water Heat Pump Retrofit

which provides some information which may be helpful.


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  1. paul_wiedefeld | | #1

    Try to nail down the existing heat loss with this:

    You may find that your heat loss divided by linear feet of baseboard puts you well under the 180 degree average water temperature that baseboards are usually sized for. You may also find that it won't but that it's close enough that you can still use a R-410A air-to-water system with a mix of backup (electric resistance, oil, and/or R134A heat pump in series could all work), more insulation, and/or higher output radiation (baseboard, panel radiators, etc.). This path will be more easily accessible for you now compared to CO2 heat pumps. Even if the answer involves keeping the oil boiler for the coldest temperatures, you can still cut oil use drastically, as the distribution of heat usage is not evenly distributed across all temperatures.

    Caleffi's Idronics journals are another great resource for adapting a system to use lower temperatures.

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