When to Buy a New Heat Pump
My Minneapolis 1950’s house has been professionally air sealed and insulated with before/after blower door testing and has central ducted HVAC. The AC unit and furnace are both apx 25 years old, so although they work fine likely at the end of their life (3 ton A/C, 100k BTU 80% efficiency gas furnace- yuck). I was planning to replace both soon (possibly with a ASHP) but I noticed this article
which seems to suggest that in the next year or so there might be significant improvements in cold climate efficiency, perhaps making them more suitable for my use without a backup/supplement heat source? Or is this tech already in the market or not worth waiting for?
Thanks!
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You have done the first best thing with your home, insulated and air sealed. I would wait on changing equipment as it will not save a lot of money or energy. For me the jury is still out on heat pumps, especially in a cold climate. A true accounting of life cycle costs for a conventional high efficiency gas furnace and cold climate heat pumps would be interesting. Nothing like a cold house on a winter morning to bring clarity.
I'm not sure if the "breakthrough" is that significant to be worth waiting for. Reading the article it says it has 100% capacity at 5F and 70-80% at -5 and -10F. The Mitsubishi and other cold temp heat pumps on the market already seem to be there. Ratings at anything below 5F are tough to find.
From the linked, article, it looks like Lennox has come up with a cold climate heat pump almost as good as ones from Fujitsu and Mitsubishi that have been around for a decade. Those work fine here in Maine, where many thousands have been installed in recent years. The recent cold snap (-17°F at my house in early February) showed how well cold climate ASHPs work in cold places.
Impressive to still be making heat at -17!
I think it is new tech for Lennox, not for the world
A 30 years old 80 percent efficient furnace is 80 percent efficient when it runs, but drafts heated air out of the building 24/7 so net efficiency is much lower
Minneapolis gets pretty cold, so for 100 percent certainty, you may want to have some kind of backup, but it would only be needed on really, really cold nights
Mitusbishis mini splits run down to -13, so figure the amount of time you are below that.
No new tech needed.
IF your 50s house has a fireplace maybe a gas insert or a wood stove for just in case, but I would think with your insulation and air sealing, dips below that level would not cause problems if the system is properly sized
Having been to Minneapolis in the winter, it can feel like you are at the north pole but it is actually not that cold. The outdoor design temperature is -6F, temperatures can occasionally fall bellow that of course but most homes have enough heat capacity to make it through that.
Modern heat pumps have no issues running down to -22F and even lower, so they can work in your climate even without any resistance heat.
Since you have existing fuel use data, I would run through the numbers here to figure out what your actual heat loss is:
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
Once you have that you can look at what equipment will work for you.
I recently had two relatives furnace draft inducer fail leaving them without heat for a couple of days. As for reliability, a properly installed heat pump will run just as well if not better than a furnace, no inducers, no igniters no flame sensors. If you are still worried, install the a backup strip heater.
As for the DOE announcement, as others have said, it is simply Lennox catching up with technology that has been used elsewhere for decades. The state of domestic heat pumps is sad.
Akos, I did the calcs per the link and came up with 47,000 BTU's with the 1.4 factor. Now I'm not surprised its oversized (I have a 80k BTU output furnace), because most are and also that unit was installed before the house got new windows (previous owner) and the air sealing and extra attic insulation (me). To cross check I looked at some data from my ecobee thermostat for Feb 3rd of this year, when the nighttime low was about -13f and the daytime high about +4f. At night I have the thermostat set up to set back from 68f to 60f and switch from using the main floor temperature sensor to one in my bedroom on the 2nd floor at about 10pm. So from 10pm on the night of the 2nd until approximately 6am on the morning of the 3rd, there appear to be NO calls for heat from the thermostat. At 6am it runs about 10 min, and then around 6:30 it starts a long run to bring the temp back up to 68f by the 8am set increase ("smart recovery"). It didn't quite get there though, only made it to 65f by 8am (looks like it didn't hit 68f until 9:30a). So it ran pretty much continuously from 6:30-10am, after that it appears to run apx 40-60% of the time the rest of the day. So the 80k output is clearly way more than it needs to keep the house warm, but it does seem to need that much output to bring the house back to temp after the setback.
I suppose that's a pretty big setback (but I like my room cool at night). Given an inverter equipped heat pump can throttle down significantly, it would seem one with a similar output to the current 80k gas furnace wouldn't be the worst thing in the world, but perhaps it would make more sense to drop it down to 60k and not set back as much and/or use the gas fireplace to aid in recovery on cold days... of course there is the cooling load to consider as well. On the warmest day last year (101f), it looks like the (25 year old) 3 ton AC ran pretty much 100% duty cycle from 6:30pm to 1:30am with a set back from 75f to 73 f at 9pm. On the other hand, it didn't run at at all from 6:30am (80f outside at that time) until 12:30pm (by which time the outside time was 93f). I suppose the brick exterior is acting as a bit of a heat sink, also the set temp went back from 73f to 75f at 7am and the thermostat switched to reading the first floor which runs about 4f cooler than the 2nd floor all day during cooling season, likely due in part to duct design/quality.
You won’t find a 80,000 Btu output heat pump, especially at -13. You can find something that outputs about half that so a backup furnace or electric resistance strips would be wise. Gentler setbacks would help too.
The 1.4 factor is for a fuel burner. With a heat pump you want it right sized, or even slightly undersized with strip heat. In your case a 3 or 3.5 ton unit is the best fit.
With modulating heat pumps, recovering from a setback is generally not worth it as a unit running at full tilt has lower efficiency than running at part load. You can still do a setback just try to make it less drastic or ramp it up more slowly in the morning. In either case, you should not need an oversized unit for that.
This is a good resource for compering units (select centrally ducted for the duct configuration):
https://ashp.neep.org/#!/product_list/
This unit is probably in the ballpark for what you need, this is the Trane branded version of the Mitsubishi unit :
https://ashp.neep.org/#!/product/33506/7/25000///0
https://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006/M_SUBMITTAL_SVZ-KP36NA_SUZ-KA36NAHZ_en.pdf
You can install a 10kW strip heater as well which can provide pretty much the full heat for the house. I think something smaller like a 5kW (17000BTU/h) is good enough to cover shortfalls in case of polar vortex days.
Most other manufacturers Fujitsu, Midea/Carrier, Samsung and LG also offer similar units as well.
You want a right size, NOT an oversize HP, otherwise it will not be efficient.
HP tech is designed to run most efficiently WITHOUT setbacks. So if you are putting in more than one minisplit, or have zones on your HP, strongly consider putting the bedroom on its own zone, so it can stay colder at night in the winter without needing to let the rest of the house cool similarly.
Ugh, had the first contactor come today for an estimate. Found their information on the Minnesota Heat Pump Collaborative web site. Despite me telling him that I had runtime data to support my opinion that my 80k BTU output gas furnace was oversized, he just sent me a bid with a 90k BTU gas furnace and a Lennox Model EL18XPV-036 inverter driven heat pump. I have no problem with the idea of running a hybrid gas furnace/heat pump setup, but 90k BTU? Yuck. I wasn't really expecting him to run a manual J, but specing a 90k unit after just pulling the building square feet off public records is disappointing. Guess it's back to searching for a more technically minded installer.
This is generally how it goes. Furnace options are pretty limited however - 90kbtu is a joke but the next two sizes are 40 or 60. I’m glad shoe shopping isn’t like dealing with HVAC installers.
Looks like lennox makes a 66k input unit, I would think that would be fine. Other brands obviously make 60k input, I suspect that would also work just fine.
Not really on-topic, but as someone who lived in Minneapolis for three years, the winters really do get cold w/ the wind chill. Our apartment building had underground heated parking so that cars would start in the winter months, and I had the privilege of experiencing frozen nose hairs! When it gets to be -20 or so, a balaclava is mandatory.
The flipside is that everyone knows it's going to be cold and there's a million lakes, so everyone just bundles up and tries to have fun outside. My family really enjoyed the winter festivals that took place on Bde Maka Ska!
Wow, that was fast, thanks for all the replies. I suspected this might just be US manufactures catching up to foreign competition, I appreciate the confirmation. As far as backup/supplement, the house has a gas fireplace insert in what was formerly a wood burning fireplace (flu was shot, so did a drop down flu for the insert rather than repair). I'm going to be replacing the water heater as well (since it's an old and natural draft, shares flu with current furnace). Might go heat pump there as well. Otherwise tankless gas or power vent gas tank or direct vent gas tank (seemed very rare around here last time I looked, but that was a while ago).
You will be fine, the 3-4 nights that normally dip into hard to heat territory for heat pumps you can fire up the insert.
The press release is just fluff - someone decided to do Lennox a solid and praise them for something that many manufacturers are already producing at scale. Backup, whether fossil or resistance, isn't a big deal. It'll only come into play a few days/hours per year.
This is the title of the report
“Lennox’s Cold Climate Heat Pump Unlocks Potential for Domestic Manufacturing of Clean Energy Heating Products that Slash Energy Bills for Americans”
So far as I can tell the only breakthrough is the Domestic Manufacturing and maybe if they have found a way to build it without violating someone else patents.
I think the green thing to do is to keep the existing equipment in service for as long as possible delaying manufacturing its replacement.
Do the math before you buy the heat pump from a dollars per year point of view on city gas a 95% gas furnace is hard to beat.
Walta
“mpls1921 | Apr 01, 2023 06:22pm | #18
Looks like lennox makes a 66k input unit, I would think that would be fine. Other brands obviously make 60k input, I suspect that would also work just fine.”
Unlike heat pumps there is almost no efficiency penalty for oversizing the gas furnace. So, there is no reason to risk under sizing.
I think dual fuel systems are overly expensive systems. I say pick a fuel with the lowest operating cost today. My opinion is the fuel price differential is unlikely to change enough to recover the extra equipment cost.
Note I think it is a mistake to buy a low-end heat pump without variable speed compressor, electronic expansion valves, communicating thermostat and indoor ECM motor are must haves in my book.
Walta
" no efficiency penalty for oversizing the gas furnace." Yes, but there is a big comfort penalty.
A while back I was at a tiny 2 bedroom bungalow in the middle of the winter that had a ludicrously oversized 75k furnace. The furnace would run a couple of minutes at the most (mind you this is near local outdoor design temperature), the rest of the time you would sit there freezing waiting for the next heat call.
Even with a furnace, you want it about right sized. There are plenty of 40000 BTU dual stage gas burners out there, they are not hard to find.
As Akos indicated, there is a comfort issue. I'm looking at my ecobee data with my existing 80k output single stage furnace and even on days with the daytime high as zero F or below, runtime never seems to exceed about 60% in any given hour (excluding setback recovery), and frequently less. I could not find a single day where total run time exceeded 10 hrs in a 24 hour period (much of which was setback recovery from a large setback), even when the daily average temp was -8F. Although I can not compare this data to other houses, I find it hard to believe a 65k output unit wouldn't be more than sufficient and compared to a 80k+ unit would result in longer run times and more comfort (even if both were 2 stage).
The furnace bid was for a two stage gas furnace with a variable speed ecm motor (lennox Model EL296UH090). The A/C side of the bid had two options, both 3 ton, one a heat pump (Lennox Model EL18XPV-036), the other an inverter driven A/C only unit (Model EL18XCV-036). The price difference is only $500, not counting any rebates or tax benefits, so there seems like no reason not to use the heat pump version between those two. I could purchase a cheaper AC unit than that inverter driven one but I really want the improved humidity control, although one could certainly make the argument that I would be better off with a 16 SEER single stage A/C and a whole-house dehumidifier from a comfort standpoint.
If you are going to go the fuel burner route, there is a 45k version of that unit:
EL296UH045XV36B
That will still easily carry the place and will have much longer runtimes on low fire.
With recent jumps in gas price around me, heat pumps are now cheaper to run so it is an easy answer which way to go. Plus there is no way to make fuel at home for a gas burner but it is pretty easy to install a PV array to cover the operating costs of a heat pump.
If you look at actual BOM cost, a two stage ECM furnace and bargain basement AC is about the same cost as a heat pump. The install is actually easier as there are no gas connection or venting required. This gets you a fully modulating unit and much lower cooling costs for essentially free. The one issue is that heat pump installs around here are still in the magical price territory completely detached from reality.
Akos, thanks for all your input. I certainly believe the equipment vs install cost issue you are talking about, it seems hard to even find someone willing to come up with an estimate considering I called a provider from the Heat Pump Coalition or whatever and got what I got! I'd love a rec for a MSP HVAC company more comfortable with heat pumps if anyone has one.
Marsh Heating in Brooklyn Park for Lennox. My own Minneapolis home has a design temperature heat loss of about 30k Btu. I have the Lennox 66k two stage with 45k low fire. It is perfectly sized for my house and will handle a good nightly setback if that is what you want.
Thanks, I'll give them a call. I'm willing to pay for knowledge and work, but not real interested in working with companies that just show up and ask what the sf of the house is.
The furnace I replaced was a natural gas 150K Btu input. The 66k Btu Lennox replacement has twice the output of my design temperature heat loss (approx. 30k) for my 3,328 sf rambler. Used to do a deep nightly setback from 70F t0 62F and the 66k Btu furnace was just right for this. On the colder days it would run full steam for about 2 1/2 hours after 6 AM to get back to the 70F setpoint. Will run on low fire most all winter long and I like the quiet and low fan speed of the ECM. Kelly Marsh is the contact and Marsh Heating is the best I have found in MSP.
Doug