Opinions on heat pump backup

You could plug your fuel costs into this spreadsheet: www.eia.gov/neic/experts/heatcalc.xls

Around here, last I checked, propane is more expensive than oil and resistance electric is just a little less than propane. Maybe go whole hog on the most efficient heat pump you can get so the backup doesn't come on that much, and get a pellet stove, or something, upstairs.

That's Right said:

In need of a new heat pump for house. 2800sqft 2 story house built in 96 in central PA. HP is 10years old and got a workout this winter. Question is to replace with electric resistance backup or propane? Have resistance now and electric bills were $500mo during cold spells. Usually during those months it is $300-350.

Option to go with propane as backup, but would have to either rent/buy tank. Would have to go with 2 100lb tanks that I would probably buy. Burying a large one would probably be too expensive.

Would have HP set to work down to 25 or so.

Both quoted about the same price through buddy/hookup.

The p61 heats the basement.

Thanks for the opinions

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What's your electric rate in winter? I would think twice about a propane backup. Propane prices change so much and the propane backup changes completely to gas at the cut off temp. Electric backup will work together with the HP to attempt to maintain the home temp. When I'm not running my wood boiler, the HP is still operating down at zero with shots of electric resistance occasionally. Maybe your attic insulation has settled making it less effective. Check your end joist bays on a very cold day. My 2009 home just has batts there and they were wet and frosty on our coldest days this winter. Going to add pink foam behind the batts sealed with great stuff or get a spray foam kit this summer. My 5 ton HP has a 5kw and a 10kw strip I believe. It would be better if they were staged and the blower was variable speed but my system is pretty basic. I think propane backup which my dad has would actually cost you more every month.

rkusek, still, it gets pretty cold where you live, and your new home got built with a heat pump, which is interesting to me.

Very new to me, I;ve been running a Mitsu 18k btu air sourced heat pump most of the winter. Seems to work well, haven't seen $50 or $60 increase in electric, BUT still running wood boiler for a small area of radiant floor in my kitchen, upstairs zone and DHW. When it gets below zero, it will still throw pretty good heat, but I shut it off and heat with the wood boiler. The BB does a better job on those sub zero nights keeping perimeter of house warm.

I would second velvetfoot's recommendation to work the eia spreadsheet. I have a HP with propane backup and as mentioned it turns into pure propane heat at the cutoff temp. To put that in real world terms I paid $850 for one month worth of propane during the polar vortex....and I had a discount contract that I signed in the summer, so my propane was $3/gal while others in the area were paying $5.

Anyway take the spreadsheet and play with it using your local kWh price to see at what point propane becomes competitive with a HP, or any other fuel for that matter. I did it for my area and the results were surprising. I blogged it here, table near the end shows what propane has to be to be competitive with various fuels:

http://unjustifiedprecision.blogspot.com/2014/03/propane-heat-is-for-suckers-and-yes.html

Propane backup heat was clearly a mistake. But at the time, with much cheaper propane, it made sense.

potentialburner said:

I would second velvetfoot's recommendation to work the eia spreadsheet. I have a HP with propane backup and as mentioned it turns into pure propane heat at the cutoff temp. To put that in real world terms I paid $850 for one month worth of propane during the polar vortex....and I had a discount contract that I signed in the summer, so my propane was $3/gal while others in the area were paying $5.

Anyway take the spreadsheet and play with it using your local kWh price to see at what point propane becomes competitive with a HP, or any other fuel for that matter. I did it for my area and the results were surprising. I blogged it here, table near the end shows what propane has to be to be competitive with various fuels:

http://unjustifiedprecision.blogspot.com/2014/03/propane-heat-is-for-suckers-and-yes.html

Propane backup heat was clearly a mistake. But at the time, with much cheaper propane, it made sense.

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Just curious, you're in NC? Why do you need a back up for a HP? Just thinking and learning.

I've been using that Heatcalc spreadsheet recently, so I pulled it up. Adjusting for an HSPF in Eastern PA, of 7.7, and using 15 cent electric and $209 pellets and $3.60 heating oil, and modern efficiencies, I get the following:
$14.30 for a million BTUs using $209/ton pellets
$30 for a million BTUs using $3.60 oil at 86% boiler efficiency
$44 for a million BTUs using electric resistance at 100% efficiency
$19.50 for a million BTUs using an air-source HP using a HSPF of 7.7 for eastern PA.

For propane to match the HP, it'd have to cost about $1.4 a gallon at 78% efficiency.

What surprised me is that for your area, a HP is not that far off using pellets, okay, 30% more ,but that's a lot close than oil or electric resistance.

Maybe it's just my unit, but I'm very skeptical about the HSPF vs. "real world" efficiencies. I only went a few months with our newly installed HP until I decided we needed to burn wood instead. Our first cold month had an electric bill of more than 6,000 kWh . Although it almost never runs any more, I have nightmares of listening to the thing kicking into defrost mode every 20 minutes or so.

brant2000 said:

Maybe it's just my unit, but I'm very skeptical about the HSPF vs. "real world" efficiencies. I only went a few months with our newly installed HP until I decided we needed to burn wood instead. Our first cold month had an electric bill of more than 6,000 kWh . Although it almost never runs any more, I have nightmares of listening to the thing kicking into defrost mode every 20 minutes or so.

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Holy cow! 6000 kWh? That sounds more like what I would have expected for electric resistance heat.

IMHO the most efficient combo is .. inverter driven ductless mini split combined with a high efficiency Cat wood stove.
ductless mini splits have been used successfully in Denver Colo winter conditions.

main heat would be provided by Buck 91 cat .. ductless mini split would take care of fill-in heat during winter and cooling in summer. a duct less mini split is really an inverter driven heat pump .. inverter allows compressor to run at variable speeds for Maxim efficiency.

brant2000 said:

Maybe it's just my unit, but I'm very skeptical about the HSPF vs. "real world" efficiencies. I only went a few months with our newly installed HP until I decided we needed to burn wood instead. Our first cold month had an electric bill of more than 6,000 kWh . Although it almost never runs any more, I have nightmares of listening to the thing kicking into defrost mode every 20 minutes or so.

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Doesn't make sense.

_CY_ said:

IMHO the most efficient combo is .. inverter driven ductless mini split combined with a high efficiency Cat wood stove.
ductless mini splits have been used successfully in Denver Colo winter conditions.

main heat would be provided by Buck 91 cat .. ductless mini split would take care of fill-in heat during winter and cooling in summer. a duct less mini split is really an inverter driven heat pump .. inverter allows compressor to run at variable speeds for Maxim efficiency.

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This basically is my thought. If I ever rebuild a new house, R-40 walls and R-60 ceilings. Quite possibly a HP with a central wood stove. The main area will be an open format, wood stove for them cold nights.

I could be wrong on this but you may want to ask your contractor about it hopefully they can give you a exact answer.

With electric backup the heat pump will still be running when the electric backup is engaged. For instance if its 20 F outside and your heat pump is only putting out 60% of its rating its still doing so cheaper then a propane only system. The heat pump will not run in conjunction with a propane furnace. It will have a temperature at which it shuts off at and the propane system takes over. The propane system will not supplement the heat pump.

Doing a fuel cost comparison will not give you a accurate representation of operational costs because it does not include the fact that using a electric backup still allows the heat pump to run albeit even if the COP is only 2x.

flyingcow said:

Just curious, you're in NC? Why do you need a back up for a HP? Just thinking and learning.

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NC has a true four season climate, we have multiple days with lows in the 20s and even the occasional teen. 30s are pretty typical otherwise in winter. That's too cold for a heat pump.

Most heat pumps here have electric strip heater backup. But gas packs are also popular. They are more economical than electric strip heat backup when you have natural gas. Before propane ran up in price it was about equivalent.

But another advantage of a gas pack is that you can run the gas furnace on generator power and still have juice left over for the fridge, lights, etc since all you have to power to get heat is the blower motor. That was important to me because I'm in a rural area where ice storm and hurricane caused power outages can drag on for a long time.

moey said:

Doing a fuel cost comparison will not give you a accurate representation of operational costs because it does not include the fact that using a electric backup still allows the heat pump to run albeit even if the COP is only 2x.

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The EIA heatcalc spreadsheet includes a section to adjust your heat pump's HSPF based on location. The colder your local climate, the lower it adjusts. I assumed that accounted for the need to run the strip heater backup.

Now a gas pack doesn't calculate in that spreadsheet very easily I agree. However comparing propane furnace cost to electric baseboard heat cost probably gives a rough approximation of the cost comparison for emergency mode.

chken said:

I've been using that Heatcalc spreadsheet recently, so I pulled it up. Adjusting for an HSPF in Eastern PA, of 7.7, and using 15 cent electric and $209 pellets and $3.60 heating oil, and modern efficiencies, I get the following:
$14.30 for a million BTUs using $209/ton pellets
$30 for a million BTUs using $3.60 oil at 86% boiler efficiency
$44 for a million BTUs using electric resistance at 100% efficiency
$19.50 for a million BTUs using an air-source HP using a HSPF of 7.7 for eastern PA.

For propane to match the HP, it'd have to cost about $1.4 a gallon at 78% efficiency.

What surprised me is that for your area, a HP is not that far off using pellets, okay, 30% more ,but that's a lot close than oil or electric resistance.

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15 cent electricity is about double our winter rates which usually half the summer rates once you exceed a minimum threshold.

NC has a true four season climate, we have multiple days with lows in the 20s and even the occasional teen. 30s are pretty typical otherwise in winter. That's too cold for a heat pump.

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Agreed, with true four season climate it's too cold for a HP: multiple days with lows in the -20'sF and even the occasional -40'sF. +0F pretty typical. I think MN gets all the cold produced by HP's operating in winter in the rest of the US. Oops, it was that cold before HP's were invented.

NC has a true four season climate, we have multiple days with lows in the 20s and even the occasional teen. 30s are pretty typical otherwise in winter. That's too cold for a heat pump.

I'm new to the HP's, but I've been using my HP most of the winter. 20's and 30's it works very well. I haven't put a watt hour meter on it, but at 17f outside it suppose to use 2600 watts in the heating mode.

Now i think for a minute, you must have central air in your house. The unit i have is a wall unit. I think there is talk of designing a central unit to work efficiently in cold weather.

potentialburner said:

NC has a true four season climate, we have multiple days with lows in the 20s and even the occasional teen. 30s are pretty typical otherwise in winter. That's too cold for a heat pump.

Most heat pumps here have electric strip heater backup. But gas packs are also popular. They are more economical than electric strip heat backup when you have natural gas. Before propane ran up in price it was about equivalent.

But another advantage of a gas pack is that you can run the gas furnace on generator power and still have juice left over for the fridge, lights, etc since all you have to power to get heat is the blower motor. That was important to me because I'm in a rural area where ice storm and hurricane caused power outages can drag on for a long time.

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that's no longer true for inverter driven ductless mini splits ... some Operates down to -15°F outdoor temperatures with 27 seer efficiencies.

technologies marches on .. that's why I stated early that IMHO the most efficient setup is with a ductless mini split and Cat stove like Buck 91 combo.
Buck 91 (substantially less $$) or Blaze King model King would supply main heat with ductless mini split doing fill in duties.

again a ductless mini split is really an inverter driven heat pump with ability to run compressor at veritable speeds.

_CY_ said:

that's no longer true for inverter driven ductless mini splits ... some Operates down to -15°F outdoor temperatures with 27 seer efficiencies.

technologies marches on .. that's why I stated early that IMHO the most efficient setup is with a ductless mini split and Cat stove like Buck 91 combo.
Buck 91 (substantially less $$) or Blaze King model King would supply main heat with ductless mini split doing fill in duties.

again a ductless mini split is really an inverter driven heat pump with ability to run compressor at veritable speeds.

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I've been intrigued with ductless mini splits before because of my house design... one large open space but with a separate master suite wing. I've thought about a ductless mini split for the master suite wing as a cheaper alternative to a dual zone central system, but haven't pulled the trigger because my current single zone central heat pump system with propane backup is still working well enough, though more expensive now that propane has gone up. Also as I mentioned before I think it's important to keep propane heat capability for those long power outages.

But I like to think ahead so I can make a good decision when replacement time comes (my system is coming up on 15 years old).

Would a ductless mini split be suitable for bedroom use? What kind of power requirements do they have (i.e.,can one be run on standard portable generator with leftover juice for the fridge and lights?) Also I'm wondering about noise as the location would be right over the head of the bed in my application. Finally, I read online manuals for some and they seem a little more maintenance intensive than my central system (need to clean the filters pretty often as opposed to simply replace with standard ones from the home improvement store).

It's interesting that the discussion on heat pumps has been more informative here than at hvactalk.com. Keep the info coming!

I do not have mini splits. I have a mitsu 18btu unit(downstairs) and another mitsu 12k(up). Dont know the model numbers. But the new inverter style I believe. Only run the down stairs in the winter. I think they're 20 amp draw ( 18k) and 15 amp(12k). Not big energy draw?

They are able to run with an outside temp of 15 below. Usually gets that cold and I run my base board heating. Not sure if I posted before but at 17f it pulls 2600 watts to run. Pretty impressive I think.

flyingcow said:

I do not have mini splits. I have a mitsu 18btu unit(downstairs) and another mitsu 12k(up).

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I would think those are considered mini splits. I think any units that typically have wall mounted or cassette fan units are considered mini splits. I believe they may go up to as large as 24kbtu. A "regular" split HP unit is the type that resembles a standard central AC unit. Mine is a 4 ton unit with a total of 30 kw of strip heaters for backup/defrost. The electric meter really spins when those things heat up.

Mini's have two heads and one unit outside. At least that's what iv been told