Heat Pump vs. Electric-Hybrid System
Hello! I am a new homeowner with a 30 year old oil burning furnace. My husband and I are looking to replace the old furnace with a more energy efficient system using either an all electric heat pump or some kind of hybrid between fuel and electricity. We live in the Metro West Boston, Massachusetts area and recognize that we’ll need to better insulate our home in addition to replacing the HVAC at some point in the near future.
I would love to remove oil entirely from our home, if possible. We use an induction stovetop and do not have any gas lines in our town that are available to tap into. Based on a few HVAC technicians that have come to our home, it seems like the possibilities are endless, which is a bit overwhelming.
1) We could keep the old furnace but add an electric heat pump that works for temps above freezing; the issue is that the furnace could still go in the next few years and the furnace seems to do a poor job of blowing hot air through our ductwork already.
2) We buy a new oil furnace and electric heat pump, the new oil furnace would be more efficient, we would use it on below freezing days and it would improve the flow rate through the ducts.
3) We go all electric, using a high efficiency heat pump through our ducted system, and remove our oil tank and furnace entirely. The issue here is that it could get extremely expensive to heat our home in the winter (although we do have some of the lowest electric rates in the state) and the upfront costs are pretty large.
4) We remove the oil tank and oil furnace and put in a hybrid propane/ electric heat pump system. The thinking being that propane is better than oil, at least, even if it’s still a fossil fuel.
Will an all electric system work well for a home in our region of Massachusetts? Or should we be thinking about one of the hybrid options? We unfortunately do need to do quite a bit of insulation work, especially near doors and windows, as well as our unfinished basement. Regardless of the system we use, I know insulation is a must.
Our home is about 30 years old with a post and beam structure. The basement is poured concrete. We have no attic (!) and will also be replacing the roof soon, although our home gets way too much shade to really consider solar an option.
Thank you!
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Replies
IMHO, the only hybrid system that makes sense is a heat pump/electric resistance hybrid.
Propane and Fuel Oil are often close enough in price to resistance electric heat that it doesn't make sense to spend more on the oil/propane system.
Arguably in many climates you could put in a heatpump without any "backup" source. As long as you select a unit that gives adequate capacity to a low enough OA temp.
An appropriately sized heatpump that can operate down to your design temp or lower, with some (staged and properly controlled) electric backup heat is a good way to go. The electric won't add much to the total system cost (most expensive part will be the heavy gauge wiring from your panel).
Another advantage of having some electric backup heat, is that you can round down the heat pump equipment size instead of up, which will probably lead to longer more efficient run cycles, especially in the shoulder season. If you do it properly you shouldn't have too many run hours on the resistance heat. But you do need to ensure it's controlled properly, some heatpumps (Carrier) can by default engage the electric heat unnecessarily during defrost cycles. Baseboard electric heat can be a problem if you don't coordinate the setpoints to ensure it stays off as long as the heatpump is keeping up. The duct heaters are good since they will only be staged on as necessary and are controlled by the same "brain" as the heatpump. Some equipment (LG) lets you set a deadband so the electric heat won't kick on until you're below your heating setpoint by a definable amount.
Thank you Josh! This is really helpful to hear. We know that HVAC technicians around here tend to push a hybrid system because they're used to the thinking that the older models of ducted heat pumps weren't as good at heating homes when temperatures really dipped. I should mention our house is ducted and we don't have baseboard electric heat. When you say "electric backup heat," does that mean heated coils within the heat pump? I'm new to this conversation so any information is helpful. Duct heaters on the same "brain" as the heatpump would still mean one system, is that right? Since we could use a smart thermostat?
Thanks!
One thing to keep in mind is that comfort is going to be driven more by drafts and by surface temps around your house (walls, ceilings, windows) than it is by air temp alone. Ever been in a house where the system (whatever it is) kicks on for 30 mins, then off for 20, with the air temp diving up 5° then down 5°? So starting with the air-sealing and insulation makes a lot of sense.
Then figure out how to tighten and rationalize the duct system. That might be a larger part of the cost than you think at the moment; but don't leave it up to the equipment installer as an afterthought, it's crucial to the whole system working.
As you work on the duct system think about how to integrate an ERV for ventilation.
With those things done you can then do a heat loss calculation. Consider hiring a 3rd party to do that, but at least do your own, coolcalc.net is good for homeowners.
All those things will drive down the size of the system you need installed, allowing you to compare costs more usefully. You might even find you don't need to replace the system.
(As an aside, treat the marketing around "a minisplit head in every room" running off a shared outdoor unit as suspect, lots of stories here and elsewhere about problems https://www.greenbuildingadvisor.com/article/multi-zone-heat-pump-issue)
Also:
https://www.greenbuildingadvisor.com/article/choosing-a-new-hvac-system
And:
https://www.greenbuildingadvisor.com/article/do-heat-pumps-work-in-minnesota
Thank you James! I had actually looked at the article "Do Heat Pumps Work in Minnesota" and wasn't sure if all of the techs were misinformed or just on the side of oil and gas!
Perhaps we'll start with fixing our drafty house first and then take stock of what we need to do as far as replacing the old furnace. I appreciate the resources and your taking the time to respond!
Trying to determine your heat loss with historical oil usage:
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
It is unlikely you'll need a backup fossil fuel system, especially after insulation upgrades. The "Use heat pump only above 32 degrees" advice is garbage. There may be a constraint between heat pump capacity and your heat loss, but no installer will know that if they haven't done a heat loss calculation (using the method above, not one of their useless online calculators). There's also an economic balance point but doubtful it's as high as 32 degrees and also doubtful that it'll be significant enough to add a redundant (but unreliable) fossil fueled second system with high operating costs.
Don't forget that if you go all electric you will be able to cap the chimney which is a massive heat loss point, plus you won't need to provide combustion air.
Plus there is an bonus additional safety factor of not having to worry about carbon monoxide.
I'm an HVAC contractor on the north shore of MA. Sure you can heat a home with a HP only in our area without the need for a back up heat source but Its a heck of a lot easier if the house is well insulated and tight. A traditional ducted HP is typically installed with a backup resistance heater in the air handler to supplement in colder weather and for defrost cycles, "ductless" types will require another heat source if supplemental is required/desired. It also important that the ductwork is properly sized and sealed as most is not if going that route. The question is do you want "electric only" for your heating system? At my age, having 2 sources of heat (hybrid) is my choice. I firmly believe in Murphy's Law and If the HP fails on X-mas eve, my backup system will keep us warm and my backup generator will operate it. Unlikely you will operate a larger HP on a generator. This "electrification" trend, I believe, is going to result in a less secure grid unless a whole lot of money is spent on grid improvements soon, but that's my opinion. Both of my houses (MA & NH) have HP's as primary heat (Mitsubishi) and oil & propane boilers respectively as secondary/DHW sources along with back up generators. I'm less concerned about green than I am warmth with redundancy. Propane is more costly per btu currently just having bought both FYI although a propane appliance will likely be more efficient than oil.
In response to Josh's post #1, current propane pricing puts propane at about 2-3 times cheaper per BTU than electricity, assuming 25 cents per kwh, which I understand is pretty close to a lot of places in New England these days. Electric resistance is very rarely cheaper to heat with compared to any flammable fuels.
You most certainly CAN heat with only a heat pump, but as has been mentioned, heat pumps work best when you have a well insulated home too. I think your best bang for the buck right now is to put in heat pumps sized for some reasonable estimate of what your home will need, then keep your existing oil system as a backup for any really cold nights when the heat pump falls behind. Put the cost savings into extra air sealing and insulating work that you can do in smaller steps as time and funds are available.
I would seriously consider prioritizing and attic air sealing and insulating project together with your heat pump installation if you have "no attic" (which I assume to mean "no attic insulation"). Air sealing doesn't have to be super expensive, and blown cellulose is about the cheapest insulation to install. Air sealing and insulating your attic is a BIG first step towards beefing up your home's overall insulation, and that will help you a lot with both comfort and heating costs regardless of what type of system you end up putting in.
Bill