Hybrid home HVAC

[OVERKILL]

Why are they setting a "cold climate" heatpump to only run above 1.5C/35F?

It's stupid to even do that with a regular heatpump.

I asked the same question. One of the reasons I've now changed it to -5C. Apparently, that's when it is cheaper to run the gas, but due to the carbon tax and other adder fees, I don't think that ends up being accurate, so we'll see what happens.

 

[Skippy722]

I’ve looked into one, but I’m not smart enough to figure out if it would save me money on my utility bills or not… currently averaging about $0.18/kWh for electricity, last month I used 111 therms of natural gas which was $130 (furnace ran for about 150 hours during that period).

 

[KrisZ]

Yeah, my gas furnace is huge, like 110,000BTU. It makes a lot of heat, which, when it's -30C is great, but also means it short cycles when it isn't super cold, even though it's multi-stage, even on low, it's still 55,000BTU, which means short run times when it's like -5C and above.

In your situation the heat pump will provide a nice buffer for your oversized furnace for those milder temps. The house should be a lot more comfortable as a result, with more even temperature.

I had the same problem in my CA house, due to AC size, 4 tons, the furnace was 100k BTU, and single stage, it was short cycling all the time and the house wasn’t comfortable during colder months.

 

[PWMDMD]

I have a dual-fuel Bosch IDS 2.0 heatpump/traditional oil boiler with baseboards setup. The heatpump was added two years ago when I replaced the aging central AC and the heatpump is set to work down to 15F. At that temp it easily blows warm air. It will go down to -5F and I’ve set it as low as 0F and while it will still heat they are very long run times. This heatpump cut my AC costs in half (it’s a SEER 20.5) and my heating costs are down about 30% with the current price of oil (I have 3600sqft and 5 heating zones but only one heatpump zone that covers three of the heating zones so two zones are still heated by 100% oil). My town has a municipal lighting company with very reasonable rates compared to surrounding towns with the larger private electric companies.

 

[IveBeenRued]

My winter house is in Virginia so we went ahead and put in a five zone Mitsubishi Hyper Heat heat pump system about 3 years ago. Yes, we are off of fuel oil, but in short, it’s good but the overall maintenance and lack of warmth has us looking to put in a gas furnace now. Once the temps drop below 10-15 degrees F, it simply can’t keep up. It is a 54K BTU system on a 1200 square foot home.

 

[PWMDMD]

I asked the same question. One of the reasons I've now changed it to -5C. Apparently, that's when it is cheaper to run the gas, but due to the carbon tax and other adder fees, I don't think that ends up being accurate, so we'll see what happens.

Do the math yourself. We just had the boiler serviced and the tech was trying to convince my wife to set the turnover point to 35F based on a “general rule of thumb”. He has no idea the heatpump system (his company did not install it and he was in the basement and it’s in the attic) and he thought we had one of the outrageous privately owned electric companies and not our municipal company.

He was very wrong…I wish people who weren’t sure would just say they aren’t sure. The guy is probably costing people hundreds to thousands of dollars with his rule of thumb recommendations.

 

[mattd]

The province recently offered (it expires Friday) a time-limited program for select communities (including mine) to rebate $3,000 for a hybrid heat pump, or $4,500 for a Cold Climate hybrid heat pump system.

My old century home is 4 stories (including the basement) and we've been running a window shaker for years because I didn't opt for central air back when we had the new furnace installed.

I contacted them and had somebody come out and my furnace was new enough to work with the program and so today, after about 6 hours, I had a Cold Climate heat pump integrated into my HVAC system, which will handle heating duty above 1.5C. I may adjust that down, that's just where they set it. Below this temperature, it runs my gas furnace.

So, today, I'm heating with electricity. Tonight, I might be heating with gas, should be interesting. But, my wife will now be happy that we have central air, lol.

Unit that was installed was a mid-tier Carrier Performance series, 2-ton.

View attachment 147491

Anybody else looked at doing something like this?

I’m putting in a Mitsubishi 4 zone 2Hi system in the next couple of months. I’ll supplement in the shoulder months with heat and if needed during the winter in case of a boiler issue (primary heat). It will heat down to -23*F. It’s primary function will be for AC

 

[OVERKILL]

Do the math yourself. We just had the boiler serviced and the tech was trying to convince my wife to set the turnover point to 35F based on a “general rule of thumb”. He has no idea the heatpump system (his company did not install it and he was in the basement and it’s in the attic) and he thought we had one of the outrageous privately owned electric companies and not our municipal company.

He was very wrong…I wish people who weren’t sure would just say they aren’t sure. The guy is probably costing people hundreds to thousands of dollars with his rule of thumb recommendations.

@Rand and I went over this a bit last night in a chat and that's exactly it, these "rule of thumb" recommendations don't appear to be based on the available numbers, which I've posted earlier in the thread, but rather estimates.

 

[Rand]

I’ve looked into one, but I’m not smart enough to figure out if it would save me money on my utility bills or not… currently averaging about $0.18/kWh for electricity, last month I used 111 therms of natural gas which was $130 (furnace ran for about 150 hours during that period).

Roughly:
your electricity is considerably more expensive (double at night/offpeak 50% more at peak/midpeak average) more than @OVERKILL
and your gas is about half price.
so not worth it or maybe around the same.

I'll go find the estimated numbers we came up and post them later.. or Overkill can.

 

[Rand]

I’ve looked into one, but I’m not smart enough to figure out if it would save me money on my utility bills or not… currently averaging about $0.18/kWh for electricity, last month I used 111 therms of natural gas which was $130 (furnace ran for about 150 hours during that period).

Roughly:
your electricity is considerably more expensive more than @OVERKILL
and your gas is about half price.
so likely not worth it.

I'll go find the estimated numbers we came up and post them later.. or Overkill can.

PRICES are in CAD.

Gas price not including connection fee since overkill will have gas regardless. aprox $16.50/MCF this tracks very closely with use so is fairly accurate.

Electric as posted earlier 15.2/10.2/7.4 /kwh
here is one of the assumptions: use ratio will remain almost the same. that would put his average cost per kwh around .15cad
there is no easy way to estimate this besides seeing the difference in energy bills and even then weather can affect it.

we also used a COP chart for the heat pump to estimate efficiency.

The math shows his 95% efficient furnace assuming its 95% eff. produces about 57000BTU for $1 CAD
The heat pump cost/efficiency varies with temp and time of day.
at nighttime when electricity is nearly half its cheaper to operate.
Also no estimate of the blower motor energy usage due to the longer runtimes was considered.
it is a multi speed blower so probably reasonably efficient.

electric numbers are adjusted make 57k btu of heating which is $1 CAD for the gas furnace.

47F = 3.77 COP = 4.4 kwh
17F = 2.6 COP = 6.4 Kwh
5f = 1.8 COP = 9.3kwh

So then you need to figure out if that is cheaper than 1$ and how much is the savings.

At nighttime there is still savings even down to nearly 5F
but when there are peak or mid rates there is no savings that low.. which means you pick a higher switchover temp. -5C(23f) seems a good choice
offpeak -10C(14f) would still be ok but with peak/mid peak rates there is no savings at that temp.