Hi Paul, this is a good question. Based on my experience, my initial reaction is that there are a lot of system types you could be pursuing.

First, you have to decide if you’re keeping the oil fired boiler in service (or replacing with a new one). Since you don’t have access to natural gas, your only other heating option is obviously electric resistance.

I’m focusing on the heating issue first, because in most residential applications with cold climates, occupants prefer to include a reheat capability with a geothermal, or even air source, heat pump system. This is due to the fact that air discharge temperature from a heat pump is typically much lower than that off a traditional heating system such as a gas furnace at 120°F. On a cold day, a heat pump might comparatively be supplying air at 90°F, which would no doubt heat and space, but feels ‘cool’ to the touch, since our body temperatures run higher than that. So unlike a furnace, which would put out a lot of heat for a short period of time, a heat pump would produce less heat for a longer period of time. This perception is why many residential systems include supplemental heat. Utilizing ground source water for heating in a baseboard application, though, I don’t think is an option. While this fluid is definitely warmer than the ambient air, it takes the heat pump’s refrigerant cycle to produce heat on the coldest days, and 50°F fluid won’t product heat in a radiant baseboard application.

All that being said, it would be my recommendation to keep your hydronic heating in place as a supplemental heat source, replacing the boiler with a newer, energy efficient model. Implementation of a heat pump system with a good controls system will help the two systems work in harmony and prevent simultaneous operation during changeover months. The heat pump system would be responsible for heating a majority of the time, but during those exceptionally cold days, the radiant heat would help address the peak heating load.

Of course, yes, you would have to retrofit for central forced air to implement a heat pump (if you don’t already have AC), which brings me to another question you need to ask yourself… what are your overall goals for this retrofit? Replace the boiler (at 16 yrs old), add air conditioning, make the system as energy-efficient as possible, or are you just performing an update? All of these questions lend themselves to different system options.

It seems to me that you’re looking for an energy-efficient heating and cooling system, which, for your application of an existing home, would be very expensive to implement a forced air system if you don’t already have one, and of course a geothermal system adds very significant costs of its own as well. Ductless split systems are a good retrofit option to add air conditioning when adding ductwork for a central forced air system is cost-prohibitive. These systems are also energy-efficient with SEER ratings around 14, and cost in the range of $1,000-$1,500 per ton of cooling. Heat pump ductless type split systems are available as well, with some systems allowing for connecting up to four indoor units to one outdoor condensing unit. I’d recommend visiting http://www.oldhouseweb.com/ for more information.

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