5 ms·

> Death is coming for the old-school gas furnace—and its killer is the humble heat pump. Uh, you still need a furnace (though it could be electric) if you live

> Death is coming for the old-school gas furnace—and its killer is the humble heat pump. Uh, you still need a furnace (though it could be electric) if you live somewhere that ever really gets cold, right? [edit] I mean, seeing it presented as a furnace replacement is weird to me. I’ve always seen it sold as an air conditioner replacement that also happens to heat (with weird characteristics that often confuse people—they’ll think their heat is broken, because the air coming out is only kinda warm, not very-warm like furnace heat) when it’s not really cold out.

loeg 3y ago
Heatpumps have resistance heating backup for the exceptional periods when it is too cold to make use of the compression system. Most people live somewhere a heatpump would work well.
- vundercind 3y ago
  Oh, I’ve not see that kind, only the sort where the “e heat” feature on the thermostat is tied to a separate furnace.
- heironimus 3y ago
  Problem is, if everyone has resistance backup and it gets really cold, I doubt if the grid could keep up.
- giantg2 3y ago
  This also assumes a resilient grid, which may not be the case for large areas of the rural US.
spiderice 3y ago
Yes. I live in Utah and have a heat pump and gas furnace. I am told the heat pump is really efficient at medium-cold temperatures, but not so much on really cold days.
- loeg 3y ago
  I believe heatpump technology has improved over time. Also, "less efficient but still functional" is an adequate option for really cold days.
  - Loughla 3y ago
    Less efficient but still functional means my home was 50 degree inside instead of 67 when it was -1 for two weeks here. On older homes, with much worse insulation, this would immediately be a problem. Heat pumps are great, but they absolutely need some kind of emergency heat back up.
    - loeg 3y ago
      > Less efficient but still functional means my home was 50 degree inside instead of 67 when it was -1 for two weeks here. No, that's just not functional. "Less efficient" means consuming more joules of electricity but still providing the required function. > Heat pumps are great, but they absolutely need some kind of emergency heat back up. They include it. You were sold an inadequate pump for your situation.
adastra22 3y ago
Heat pumps are still more efficient, but you’d need damn good insulation (or a really big heat pump) in super cold weather. Furnaces scale-up pretty well on the other hand. If your locale gets life threateningly cold though, I’d feel more comfortable with a furnace because of the fewer moving parts. Burn gas, get heat, dead simple.
- 01HNNWZ0MV43FF 3y ago
  Funny enough in the short term I've lived in my house, I already had a winter where the furnace quit. It's a high-efficiency one with a control board (Nobody can convince me FCS isn't Fire Control System) and a separate draft motor. One of the vacuum sensors went out and the furnace couldn't prove it was safe to run, so it would turn on the draft motor, suspect a clog, and then shut it back off. An easy fix but not as simple as lighting a Bunsen burner. And I haven't seen the electrical cord for it, I'm not sure how I would hook it to a generator if I lost power. The water heater oddly enough is battery-powered, so I guess I could just fill the tub with hot water.
Workaccount2 3y ago
Cutting edge heat pumps can now work down into the sub zero (F) temperatures. Manufacturers have really been pushing hard on this in recent years. But these units still are more expensive than your run of the mill ones.
nitsuaeekcm 3y ago
The best mental model for a heat pump is that they can maintain a certain temperature differential, say 80F. If it gets to be 0F outside and you want it to be 70? You don’t need to switch to a fully separate heating system, you just need to warm up either the incoming or outgoing air an additional 10 degrees via a small resistance heater. The super wide range heat pump systems will do that automatically, and the principle really applies to any differential you could want.
- VBprogrammer 3y ago
  The wide range ones are basically two heat pumps back to back using different working fluids. They should only be used in applications where they are really required as there are obviously impacts to the COP.
- JadeNB 3y ago
  > The best mental model for a heat pump is that they can maintain a certain temperature differential, say 80F. If it gets to be 0F outside and you want it to be 70? You don’t need to switch to a fully separate heating system, you just need to warm up either the incoming or outgoing air an additional 10 degrees via a small resistance heater. Are your 70 and 80 switched? What you describe doesn't sound like it needs any addition.
kj4ips 3y ago
I have a pair of heat pumps in a dual zone setup, each of them has a backup electric furnace as part of its indoor air handler. Newer ones can keep running without that even into quite cold areas. The thermostat just sees the resistive heaters as another phase, so I have three phases, and if it doesn't see a temp rise within a certain time of calling for phase 1/2, then it goes to phase 3. Mine also has support for an external temperature probe, that can skip 1/2 if it is already too cold. I also have other ways to make heat if I have a prolonged electrical outage, but outside of maintenance, I've not used that.
loudmax 3y ago
What's really cold? There are heat pumps that are advertised as working at -15F. On the days when it gets that cold, your heat pump will need to switch to electric heat. So on those days, your heat pump is no better than an electric furnace. On all other days that the heater is running, the heat pump is a far more efficient option.
epiccoleman 3y ago
From my limited experience, I'd say yes - you still need a furnace. I converted my garage into my office by adding a mini split AC/heat pump. The garage walls, door, and attic are insulated - but it's still a garage, which means that it's not nearly as well insulated as a regular room in a house. The unit is 18k BTUs, which is quite oversized for the size of the garage. I made this choice because the heat pump BTUs are significantly less than cooling BTUs. This is definitely obvious, experientally - the unit can make my garage uncomfortably cold even in the peak of summer. But even though this unit is supposedly rated for operation in temps down to about -20F, when winter gets really cold, it struggles to keep the space warm. Once the temps are below about 20F or so, I usually add a space heater to the mix, which, combined with warm clothes, makes working out here at least tolerable.
rootbear 3y ago
I live in Maryland and the first townhouse I owned, in the late 80s to early 90s, had a heat pump. It included an auxiliary electric heater for days that it got really cold. I don't remember it coming on all that often. (There was a light on the thermostat to indicate when it was on.) My current townhouse has a gas furnace. I plan to move soon into a single level home, more appropriate for an old greybeard, and I'll have to evaluate then if I want to switch to a heat pump, if the house doesn't have one already.
rimunroe 3y ago
Note: this is only true for air-source heat pumps. Ground source-heat pumps aren't affected by ambient air temperature, but they're also much more expensive and require suitable ground. Also, I hear air-source heat pumps have made significant advances lately in how well they handle sub -15 °C temperatures.
mikeyouse 3y ago
> Uh, you still need a furnace (though it could be electric) if you live somewhere that ever really gets cold, right? For now - and only in part of the country. Most of the newest models can output 100% of their rating down to something like -5ºF -- they're easy enough to oversize as well, so if your 99% heating load is e.g. 48,000BTU, a 60,000BTU heat pump that's only outputting 80% of rated BTUs due to the extreme cold can still cover the full design load. Here's the spec sheet for the newer Mitsubishi hyper heat models - 87º output at -4ºF and 76% output at -13ºF -- very few places in the states ever get that cold: https://static.appliancesconnection.com/attachments/D5bf57097bbdd4.pdf https://static.appliancesconnection.com/attachments/D5bf5709...
- lotsofpulp 3y ago
  I like the redundancy of natural gas. So far, in less than 40 years, I have been kept warm for multiple days on 3 separate occasions by having access to gas while the electricity did not work. Also, I was able to keep cooking. One of the states in the article is Oregon too, where I have family that just a few weeks ago lost electricity for 4 days, but were able to use an electric generator to keep the air handler going and gas to heat the the house and cook. I fear heat pump only heat will fail exactly when I most need it not to.
  - vundercind 3y ago
    Yeah if my heat were 100% electric I’d have to install a wood heating-stove to feel like I wasn’t being irresponsible. Or maybe get a couple portable kerosene heaters.
    - VBprogrammer 3y ago
      I think a sensible option, if you live in a place where electrical grids goes out for a couple of days fairly routinely, would be a transfer switch and a generator. If sized well enough you could use it to run a resistance heater (the cheap portable type) to keep one or two rooms warm in an extreme scenario.
01HNNWZ0MV43FF 3y ago
Technology Connections seems pretty happy with his. I think he lives in Chicago, admittedly not the coldest place, but it does snow every winter in that region. He said 2.9 coefficient of efficiency average over a heating season for him - https://youtu.be/7J52mDjZzto?t=1522 https://youtu.be/7J52mDjZzto?t=1522
orwin 3y ago
Depends on the heat pump, and the quality of your house. Hopefully houses in northern US states are of better quality than houses in California or West Virginia/South Ohio, so a furnface might not be needed. Because for the scandinavians reading the thread and with the "It works in my country", US house build quality, in my experience, is even worse than UK houses build quality (and that's a pretty low bar).
carapace 3y ago
No, you need better insulation. (And maybe a rocket stove combined with a heat storage hypocaust.) https://solar.lowtechmagazine.com/2017/03/heat-storage-hypocausts-air-heating-in-the-middle-ages/ https://solar.lowtechmagazine.com/2017/03/heat-storage-hypoc...
switchbak 3y ago
They make ones that handle the cold quite well, but in my mind dual-fuel is where it's at, especially if you're doing a retrofit. Unfortunately there does seem to be a desire (even with the rebate systems) to kill the old furnaces.
bagels 3y ago
The capabilities work fine for much of the country that doesn't get exceedingly freezing temperatures. It only gets down to about 26F on the coldest of cold nights here once or twice per year.

loeg 3y ago

Heatpumps have resistance heating backup for the exceptional periods when it is too cold to make use of the compression system. Most people live somewhere a heatpump would work well.

vundercind 3y ago
Oh, I’ve not see that kind, only the sort where the “e heat” feature on the thermostat is tied to a separate furnace.
heironimus 3y ago
Problem is, if everyone has resistance backup and it gets really cold, I doubt if the grid could keep up.
giantg2 3y ago
This also assumes a resilient grid, which may not be the case for large areas of the rural US.

spiderice 3y ago

Yes. I live in Utah and have a heat pump and gas furnace. I am told the heat pump is really efficient at medium-cold temperatures, but not so much on really cold days.

loeg 3y ago
I believe heatpump technology has improved over time. Also, "less efficient but still functional" is an adequate option for really cold days.
- Loughla 3y ago
  Less efficient but still functional means my home was 50 degree inside instead of 67 when it was -1 for two weeks here. On older homes, with much worse insulation, this would immediately be a problem. Heat pumps are great, but they absolutely need some kind of emergency heat back up.
  - loeg 3y ago
    > Less efficient but still functional means my home was 50 degree inside instead of 67 when it was -1 for two weeks here. No, that's just not functional. "Less efficient" means consuming more joules of electricity but still providing the required function. > Heat pumps are great, but they absolutely need some kind of emergency heat back up. They include it. You were sold an inadequate pump for your situation.

adastra22 3y ago

Heat pumps are still more efficient, but you’d need damn good insulation (or a really big heat pump) in super cold weather. Furnaces scale-up pretty well on the other hand. If your locale gets life threateningly cold though, I’d feel more comfortable with a furnace because of the fewer moving parts. Burn gas, get heat, dead simple.

01HNNWZ0MV43FF 3y ago
Funny enough in the short term I've lived in my house, I already had a winter where the furnace quit. It's a high-efficiency one with a control board (Nobody can convince me FCS isn't Fire Control System) and a separate draft motor. One of the vacuum sensors went out and the furnace couldn't prove it was safe to run, so it would turn on the draft motor, suspect a clog, and then shut it back off. An easy fix but not as simple as lighting a Bunsen burner. And I haven't seen the electrical cord for it, I'm not sure how I would hook it to a generator if I lost power. The water heater oddly enough is battery-powered, so I guess I could just fill the tub with hot water.

Workaccount2 3y ago

Cutting edge heat pumps can now work down into the sub zero (F) temperatures. Manufacturers have really been pushing hard on this in recent years. But these units still are more expensive than your run of the mill ones.

nitsuaeekcm 3y ago

The best mental model for a heat pump is that they can maintain a certain temperature differential, say 80F. If it gets to be 0F outside and you want it to be 70? You don’t need to switch to a fully separate heating system, you just need to warm up either the incoming or outgoing air an additional 10 degrees via a small resistance heater. The super wide range heat pump systems will do that automatically, and the principle really applies to any differential you could want.

VBprogrammer 3y ago
The wide range ones are basically two heat pumps back to back using different working fluids. They should only be used in applications where they are really required as there are obviously impacts to the COP.
JadeNB 3y ago
> The best mental model for a heat pump is that they can maintain a certain temperature differential, say 80F. If it gets to be 0F outside and you want it to be 70? You don’t need to switch to a fully separate heating system, you just need to warm up either the incoming or outgoing air an additional 10 degrees via a small resistance heater. Are your 70 and 80 switched? What you describe doesn't sound like it needs any addition.

kj4ips 3y ago

I have a pair of heat pumps in a dual zone setup, each of them has a backup electric furnace as part of its indoor air handler. Newer ones can keep running without that even into quite cold areas. The thermostat just sees the resistive heaters as another phase, so I have three phases, and if it doesn't see a temp rise within a certain time of calling for phase 1/2, then it goes to phase 3. Mine also has support for an external temperature probe, that can skip 1/2 if it is already too cold. I also have other ways to make heat if I have a prolonged electrical outage, but outside of maintenance, I've not used that.

loudmax 3y ago

What's really cold? There are heat pumps that are advertised as working at -15F. On the days when it gets that cold, your heat pump will need to switch to electric heat. So on those days, your heat pump is no better than an electric furnace. On all other days that the heater is running, the heat pump is a far more efficient option.

epiccoleman 3y ago

From my limited experience, I'd say yes - you still need a furnace. I converted my garage into my office by adding a mini split AC/heat pump. The garage walls, door, and attic are insulated - but it's still a garage, which means that it's not nearly as well insulated as a regular room in a house. The unit is 18k BTUs, which is quite oversized for the size of the garage. I made this choice because the heat pump BTUs are significantly less than cooling BTUs. This is definitely obvious, experientally - the unit can make my garage uncomfortably cold even in the peak of summer. But even though this unit is supposedly rated for operation in temps down to about -20F, when winter gets really cold, it struggles to keep the space warm. Once the temps are below about 20F or so, I usually add a space heater to the mix, which, combined with warm clothes, makes working out here at least tolerable.

rootbear 3y ago

I live in Maryland and the first townhouse I owned, in the late 80s to early 90s, had a heat pump. It included an auxiliary electric heater for days that it got really cold. I don't remember it coming on all that often. (There was a light on the thermostat to indicate when it was on.) My current townhouse has a gas furnace. I plan to move soon into a single level home, more appropriate for an old greybeard, and I'll have to evaluate then if I want to switch to a heat pump, if the house doesn't have one already.

rimunroe 3y ago

Note: this is only true for air-source heat pumps. Ground source-heat pumps aren't affected by ambient air temperature, but they're also much more expensive and require suitable ground. Also, I hear air-source heat pumps have made significant advances lately in how well they handle sub -15 °C temperatures.

mikeyouse 3y ago

> Uh, you still need a furnace (though it could be electric) if you live somewhere that ever really gets cold, right? For now - and only in part of the country. Most of the newest models can output 100% of their rating down to something like -5ºF -- they're easy enough to oversize as well, so if your 99% heating load is e.g. 48,000BTU, a 60,000BTU heat pump that's only outputting 80% of rated BTUs due to the extreme cold can still cover the full design load. Here's the spec sheet for the newer Mitsubishi hyper heat models - 87º output at -4ºF and 76% output at -13ºF -- very few places in the states ever get that cold: https://static.appliancesconnection.com/attachments/D5bf57097bbdd4.pdf https://static.appliancesconnection.com/attachments/D5bf5709...

lotsofpulp 3y ago
I like the redundancy of natural gas. So far, in less than 40 years, I have been kept warm for multiple days on 3 separate occasions by having access to gas while the electricity did not work. Also, I was able to keep cooking. One of the states in the article is Oregon too, where I have family that just a few weeks ago lost electricity for 4 days, but were able to use an electric generator to keep the air handler going and gas to heat the the house and cook. I fear heat pump only heat will fail exactly when I most need it not to.
- vundercind 3y ago
  Yeah if my heat were 100% electric I’d have to install a wood heating-stove to feel like I wasn’t being irresponsible. Or maybe get a couple portable kerosene heaters.
  - VBprogrammer 3y ago
    I think a sensible option, if you live in a place where electrical grids goes out for a couple of days fairly routinely, would be a transfer switch and a generator. If sized well enough you could use it to run a resistance heater (the cheap portable type) to keep one or two rooms warm in an extreme scenario.

01HNNWZ0MV43FF 3y ago

Technology Connections seems pretty happy with his. I think he lives in Chicago, admittedly not the coldest place, but it does snow every winter in that region. He said 2.9 coefficient of efficiency average over a heating season for him - https://youtu.be/7J52mDjZzto?t=1522 https://youtu.be/7J52mDjZzto?t=1522

orwin 3y ago

Depends on the heat pump, and the quality of your house. Hopefully houses in northern US states are of better quality than houses in California or West Virginia/South Ohio, so a furnface might not be needed. Because for the scandinavians reading the thread and with the "It works in my country", US house build quality, in my experience, is even worse than UK houses build quality (and that's a pretty low bar).

carapace 3y ago

No, you need better insulation. (And maybe a rocket stove combined with a heat storage hypocaust.) https://solar.lowtechmagazine.com/2017/03/heat-storage-hypocausts-air-heating-in-the-middle-ages/ https://solar.lowtechmagazine.com/2017/03/heat-storage-hypoc...

switchbak 3y ago

They make ones that handle the cold quite well, but in my mind dual-fuel is where it's at, especially if you're doing a retrofit. Unfortunately there does seem to be a desire (even with the rebate systems) to kill the old furnaces.

bagels 3y ago

The capabilities work fine for much of the country that doesn't get exceedingly freezing temperatures. It only gets down to about 26F on the coldest of cold nights here once or twice per year.