Very old house heat pump
janeisgreen
| Posted in Energy Efficiency and Durability on
Hello, I’m new here researching and now asking for advice. I’m looking at getting a new air source heat pump installed in my very old (1855) small house.
Currently, there’s an oil furnace with ducts in the basement (two) and the main floor. There are no ducts, therefore no heat, to the two upstairs rooms. I don’t have any air conditioning, but lots of insulation and storm windows, etc.
If I’m understanding correctly, the ducts can be used with the heat pump, and it would be most efficient if I had a separate unit installed for the upstairs. Is that correct? (I’m in southern Ontario, Canada, zone 5B.)
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Replies
Before you buy new equipment have you made investments in insulation and air sealing that would allow you to buy smaller equipment?
Walta
Yes, I've done everything that was advised through a blower door test.
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The old story and a half homes are notoriously leaky beasts and the lack of ductwork to the upstairs makes me think the upstairs was an addition.
Are you happy with the current amount of heat getting to the upstairs rooms?
Did they give you your ACH50 number when they did the blower door test?
Have you done a fuel use study to sizes your equipment?
Walta
On the coldest nights, I use a little space heater for an hour or so, but otherwise it's not bad. However, it would be nice to have some heat up there, and some air conditioning. The downstairs rarely gets too hot, but the upstairs sure does, even with the insulation.
I don't think I have a ACH50 number. Everything was done 20 years ago.
Fuel use study: I know how much fuel I've used, but nothing more than that.
I have contractor recommendations from people nearby. I've also visited one family who installed a heat pump three years ago, and will visit another tomorrow. I knew absolutely nothing before, and now I know a tiny bit! I'll be getting two or three contractors in to have a look and give their recommendations. I just want to know enough that nobody will attempt to put anything over on the 'little old woman.' ;)
If the existing ducts are original from the old oil furnace, they probably will need to be replaced for a heat pump. Leaky ducts can make your heat pump expensive to operate.
I have a relatively new furnace and had one new duct installed in the last 15 or so years when I built a small extension to add a stairway to the basement, but the rest was here when I bought the house 25 years ago. I can see them in the basement ceiling and I think they're all okay, but if they need to be replaced that's okay.
Danan,
Leaky ducting is only an energy use issue if the ducting is in unconditioned space. It sounds like the OP's ducts are in the basement which is pretty much always inside conditioned space here in Ontario. In this case any duct losses stay within the thermal envelope and not lost.
In this case the problem with leaky ducts is the air doesn't make it to the rooms near the ends which can create comfort issues.
That's a fair point. I'm in California where in ducts are often in unconditioned spaces like vented attics.
That said, I think comfort issues can also cause high energy use issues as occupants try to ... get comfortable.
Sorry everybody, I didn't realize that there was more discussion! The ducts are not leaky as far as I know. I taped all the seams. They are in the old cellar which has a cement floor and the walls are spray foam sealed. There are only two vents in the basement, one in each of the two spaces. I've now had two people in for estimates, and neither has had an issue with the ducts.
Eh not really? Leaky ducts cost more but if you’re going from oil to electricity you’ll still probably come out way ahead. This isn’t unique to heat pumps.
Agreed that one will come out way ahead with a heat pump vs fuel oil, especially with Ontario's ultra low electricity prices.
...and ultra high oil. Last year one tank fill-up cost what I usually paid for the whole heating season.
You might find this article interesting.
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
It maybe time to get another energy audit with a blower door test.
To me it seems silly to replace the working oil furnace before its heat exchanger develops a hole 15 years from now.
Walta
She can easily keep the furnace and add the heat pump too.
The furnace will be replaced. I forgot to mention before that there's also a wood stove for backup heat.
+1 on doing the fuel use based calculation Walta linked to first.
Once you have that in hand, you can figure out roughly how big of a system you need and comparting it to the existing oil burner, you can see if the existing ducting can work.
For the 2nd floor, there is no easy solution.
Running new ducting up there would be the best that generally means opening walls. The simplest is installing a wall mount mini split in the hallway and leaving the bedroom doors open to heat and cool. Using the resistance heaters at night time is also not a huge cost and definitely simpler than other options. The one I would avoid is putting an air handler in the attic.
Not usually a fan of multi splits but if your heat loss is near a 3 zone multi split you can use one and install a multi position air handler in the basement and a pair of small wall mounts in for the bedrooms. As long the system is sized to match your loss this should run reasonably efficiently. Wall mounts in bedrooms can create comfort issues as they move a fair bit of air so you have to watch the location and where air flows. There is also intermittent sounds when the system cycles on/off or during defrost cycles in the winter. If you are a light sleeper, I would no recommend this.
Thank-you. I've now had two people in for consultations and estimates. They both agreed that one mini-split will work upstairs. There are only two rooms up there and the unit can be placed up on one exterior wall pointing towards the door of the second room (my bedroom). It seems that that should work. New ducting is impossible.
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