Heat Pump-Only Heat
Hi there,
I’ve got a 3000 sq foot house just outside of Boston, built in 1925. We are heating right now with an oil-fired one-pipe steam system. Not only is it expensive, but to continue to operate safely we would need to spend a lot of money on our chimney.
We are going to replace all of the old drafty windows with new windows and really start hunting for drafts.
My question is, will I be able to heat my house in this heat zone with just heat pumps? We have ducting, so we are thinking of central air source heat pumps. Will there be problems having two separate zones (Basement +1st, 2nd + 3rd).
Some of the exterior walls are insulated, some may not be.
Thoughts?
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Yes, you can heat your house there exclusively with heat pumps. You may run into capacity issues at the lowest outdoor temperatures: you can add backup, either electric (resistance of some sort) or fossil furnace, but that’ll depend on the heat loss. Look into Nate Adam’s electrify everything course.
0 issues related to the zoning.
We heat our 2500 sq ft home (finished basement and main floor) in Climate Zone 6 with two mini splits. House was built in 1994, but we're still working on air sealing/efficiency upgrades, so this isn't some tight home quite yet.
We previously had a forced air furnace, which we decommissioned. It seems like a big step! We got a quote for a central heat pump system, but I noticed that 1. the efficiency of that system is significantly lower than mini splits and 2. we wanted more control over the temperature in each level of our home since we rent our basement as a suite. We went with two Fujitsu XLTH (hyper heat) single-head systems https://www.fujitsugeneral.com/us/products/split/wall/15lzah1.html - significantly higher HSPF than any central ducted pump can give you.
We went through a spell of -25C this winter and didn't even need back up heat. We don't keep our doors closed for the most part, and we get a variance of 3-4C between the warmest and coolest parts of the home, even when it's quite cold outside. Our bills have been surprisingly low - highest for all power for the home was $300 per month (at an average of $0.12 per kwh) - and that's with a group of three people living in the unit downstairs with their own full kitchen and the heat pump cranked up.
You can always use heat pumps. Heat pumps are not magical devices, and they don't absolutely require extra insulating and air sealing to work. The usual issue is that where a typical boiler or furnace produces a LOT of heat and then shuts off for a while, heat pumps generally produce a relatively small amount of heat ALL of the time. This means it is more difficult for a typical heat pump to "catch up" and bring the house up to a setpoint from a cold temperature. A heat pump won't have any trouble holding the setpoint once it gets there though, provided the system is sized correctly for the space.
What you hear about with insulating and air sealing and heat pumps on GBA is that many on GBA are targeting very high overall efficiencies for their home as a whole. They are putting in extra insulation and air sealing to maximize the efficiency of their home. This same effort would also improve efficiencies with regular furnaces or boilers. People are then adding heat pumps IN ADDITION to the insulating and air sealing work to gain even MORE efficiencies. The two things (insulating/air sealing and heat pumps) are not dependent on one another to work, but the insulating/air sealing does help a heat pump to do it's job better just like that insulating/air sealing would help a furnace or boiler to run less to maintain the same target temperature.
The one difference with a heat pump is that due to the relatively slow recovery rate, the time it takes to get back up to a setpoint if the temperature drops, is less of an issue in a well insulated home compared to a drafty one, since all those air leaks or lack of insulation means the heat pump has to work harder to overcome the leaks and heat loss while it's bringing up the temperature inside. An oversized heat pump will also help with this, but I'd try to do as much insulating and air sealing work as you can as part of your project, just don't worry about problems with a heat pump if you can't reach the ideal that you read about in terms of optimal levels of insulation.
Bill
Thanks for the replies! My main concern was for the low temperatures in Boston (Newton), MA. Although looking at the past three years, it doesn't seem to have gone below 4F here, so it may never come to back-up heat. In the cold climates, is it typical to have resistive heat installed as a back-up? @Bill, the insulation is happening regardless, we just had a $1100 oil bill for February :-|
Since you have fill up data, you can see what your actual heat load is in the existing building as is:
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
Once you have this, it is pretty easy to size a cold climate heat pump to heat the whole place.
You do mention ducting, which I'm guessing it was put in for AC, which might mean your registers are not well placed for heating. Typically for heating a house, you want registers near the exterior preferably under or over windows. If this is already the case, your heat pump swap should be relatively simple.
There is absolutely no problem with heating a place in your climate with one of the many hyper heat units without any backup. These typically deliver 100% of their rated capacity down to 5F, some even do this down to -5F. Most will continue to operate well bellow that temperature with slightly reduced output. For example a 3Ton unit that puts out 38000BTU at 5F:
https://ashp.neep.org/#!/product/33559
We are in Boston and heat with a Mitsu Hyper Heat pump. It's been great.
If you do air handlers, it would be a good idea to put in heat strips for backup, in case of failure of the outdoor unit. I'd also suggest using 2 separate outdoor units for redundancy.
We used Boucher Energy Systems for our install, and had great luck with them. They're very knowledgeable about heat pumps, and took a great total systems approach with us. They also do sheet metal work, so they're great for ducts. We also used them to Aeroseal our ductwork.
https://boucherenergy.com/
You need to get your heat loss under control before you do anything. That is a lot of oil for one month. Insulation and air sealing first, then new heating if needed. You will be shocked at what a new system will cost.