New HVAC in MA. Heat pump make sense?
Hello green building advisors.
I thought I’d hit up this wise group for insight into my best options for replacing my home’s HVAC system.
Our home is in the Boston metro suburbs and is a roughly 1500 sq ft ranch built in the 40’s, full unfinished attic, and full basement (mechanicals, laundry, storage, one finished but mainly unused room). We did have a home energy audit when we first bought the place a couple years ago, and we had the recommended air sealing and weather stripping done and added a bit more blown in insulation in the attic. They also recommended some blown in insulation in the walls, but this is whole different level of project so we didn’t do that. I know there is some insulation in there, but not a ton based on the little experience I’ve had pulling some wire through the wall. It is currently being heating with an oil burning forced hot air unit with A/C. In the winter the house is reasonably comfortable, but I would say that both the family room and master bedroom are often on the chillier side compared to the rest of the house. The house is shaped like a U, and these are the two rooms at the far ends and both have 3 exterior walls. So I imagine the duct work and system as a whole isn’t balanced very well for this.
I followed the post on calculating an existing home’s heat load based on your existing fuel usage and came up with numbers between 31,000 BTU (Dec 2018) and 35,000 BTU (Jan 2019). Not being sure if I was even in the correct ballpark, I did use loadcalc.net and came up with just over 32,000 BTU heating load. So at the recommended 1.4 X sizing of that 35,000 BTU load, am I looking for a 49,000 BTU system? Seems large for this size house, but I guess I do have a lot of exterior walls.
That 35,000 BTU month for example, was Dec 19-Jan 28 inclusive, 148.3 gal of heating oil, running at ~70% efficiency, 1005.2 HDD, 99% temp of 6 deg.
The oil, and perhaps everything else, is going to go, it’s just a matter of what to replace it with.
My initial plan was to have natural gas installed the Monday after we closed on the house a few years ago. Boy was I surprised when they paved my street the afternoon of our closing – thus starting the 5 year moratorium on cutting in to the street to have NG installed. But now that time has passed and a different NG supplier had an accident in 3 neighborhoods north of Boston, I am wondering if NG is still the only play here. About a year and a half ago I had a PV array installed, and we are currently generating 1500 or so kwh of extra juice over our current usage. I now wonder if perhaps there’s a heat pump alternative that would prevent me from putting in another fossil fuel burning system into the world. I wonder, can this be done in a way to increase the overall comfort of the house and at the same time be more cost effective than oil, and at least within reason to NG (which I imagine can’t be touched from a pure $$ point of view).
One thought I had was perhaps three separate ducted mini splits (one unit outside) installed in the basement and ducted upstairs, one under the family room, another under the master bedroom, and then a third in the middle of the house. That would allow me to control those two “chilly” rooms separately, and there already is duct work from the basement into these places. But I’m new to the heat pump world – does this even make any sense? Wall/floor mounted mini splits directly in the rooms are a no go for aesthetic/space reasons.
Thanks in advance.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part