Heat Pump in a Leaky House
We have been considering getting a heat pump system for our home in Brattleboro VT. A neighbor of ours who has one said that these systems function best when your house is “tight”. I don’t think ours would be even close to fitting that description. There is blown insulation in the attic but nowhere else due to the presence of K&T wiring in the walls. The windows are fairly modern (probably from the 90s). No other improvements have been made. We had a local company come in and do an analysis and they came back with some areas that could be upgraded (the biggest being insulation in the basement around the joists) but the net effect would only be about a 10% improvement. Would a heat pump system work efficiently enough in our location to replace our current oil boiler system?
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Nearly all houses will heat better with fewer holes in their walls. If the heat pump is properly sized, there should be no issues.
This is a common misconception. A tight house will also let you use a smaller furnace. Heat pumps are no different in this regard, you just need more heat pump capacity if you have a leaky house.
Exterior rigid foam will gain you insulation, won't disturb the old K+T wiring, and will also help with air tightness if you detail it correctly. Personally, I would recommend replacing the old K+T wiring though any time you have the walls open for any reason.
I am in the middle of a remodel on a house built in 1900. It leaks terribly. The only insulation is r13 fiberglass in the attic. Our windows are from the 1950's. As part of the remodel we upgraded or heating system from hot water baseboard to forced air, heat pump/AC and a oil burning furnace.
We made it through this LONG/Cold winter (Pennsylvania) with our new system. I ended up turning off the heat pump and only running the furnace. The heat pump produces air at a temp of about 92F and the furnace produces 140F or better. I had to have that hot air from the oil burner or the system would almost never shutdown plus it was cold.
We have a good HVAC system, was sized by an engineer, etc. for a house that WILL be fully insulated AND air sealed. That is the catch here and may not really answer your question.
I will say that if I was not going to insulate this house I would not get a heat pump but I am not an HVAC guy either. Most people around me have outdoor wood stoves, burn coal, burn pellets or pay a lot for other heating sources.
It's okay and often preferable for any heating system to run constantly for long periods (months even). Oil fueled systems are usually unable to do this well because the GPH the nozzles are capable of is too high for most houses. Gas can do a bit better, but modulating heat pumps usually do best.
That makes sense, you know much more on this subject than I do. I am sure I will see a great savings after I am insulated well. The plan is to only have our oil furnace burn when temps are very cold. Unfortunately we do not have access to N gas or propane where I live.