In-floor radiant boiler to air-to-water heat pump conversion in Maine – GreenBuildingAdvisor

Hi all,

My friend’s propane fired boiler just sh*t the bed and they’re looking at replacements. They just had several ductless heat pumps installed. Not sure if there could be any connection– one contractor suggested as much–doesn’t make sense to me not sure. It was an old boiler in any case.

This is a several part question:

1) Does anyone know of residential contractors in Maine installing air-to-water heat pumps?

2) Could that work with an in-slab radiant distribution system (I know the water temps from air-to-water HP’s are lower, but figure since this isn’t the sole system it could work)?

3) How “nice” can an in-slab radiant system play with the ductless heat pumps? What would be the best strategy to integrate the systems (e.g. thermostat set-ups, etc.)? (My gut tells me to run the radiant on a very low setting (independent of thermostat, just base BTU/h?) for baseload heat and let the ductless heat pumps pick up the rest/swings. 

4) Assuming there are contractors available to install air-to-water heat pumps, is that what you would consider in this situation? Obviously keeping the propane has the advantage of a non-electric backup running a standard generator, which they already have (this is rural Maine). I should mention the boiler provided their hot water as an on-demand system.

Unfortunately I don’t really know how well insulated (if at all) the slab is, especially around the edges, even though I’m sure it absolutely SHOULD be with radiant. (This is rural Maine). I can talk to them more about the comfort of the slab sans radiant and I can bring my thermal camera over too.

Other interesting but perhaps not relevant bit of info is that they said they had high winter humidity problems when running the radiant and now that they are using the heat pumps the problem is not as bad. Makes me wonder if there is moisture in the slab that the radiant heat was adding to the air. No sub slab vapor barrier? Sorption from summer?