3 ms·

on the other hand, with better insulation you don't need the same BTU output

9x39 2y ago
That would make sense at first glance, but I was talking to my HVAC contractor and they warned me not to make that assumption. It's not easy to compare gas furnace BTUs to heat pump BTUs for both physics and issues specific to my home (and probably most homes not made in the last decade or so). It gets to -10F most winters here, but heat pumps struggle as it dips below freezing, while a gas furnace doesn't. What does that mean for heat in the colder parts of the year? Will I struggle to maintain 68F even if the BTUs are the same? This ties into my home design as well: Can I even substantially change my home's r-value the way it's built? I couldn't afford a new home when I bought my house, so I live in older housing stock - 1949, made heavily of cinder blocks with plaster and stucco around them. It didn't have ducting when built, and that was partially retrofitted in using a central furnace with limited air ducts to push heat clumsily from the center of the house into a few primary rooms using a California plenum to pull air from the foundation, connected to certain rooms through floor registers. There's no good way to fix any of these compromises short of ripping half the home apart, or just building a new one, so the least bad compromise is usually an over-specced central forced air solution. Do I get a central heat pump and air handler system with 100k peak BTUs? Do I get several mini-split units, each adding up to 100k BTUs? Do I overbuild on BTUs if I go mini-splits or multi-head? How will multiple smaller heat pumps work in winter as it freezes? Will insulating change that? I can't insulate my foundation more than the earth already does. I guess I could rip out all my plaster walls and put in drywall and high r-value insulation behind them, but at that point, maybe a new house would be more worth the effort. I think these kind of problems are endemic to the older housing stock and they're devilishly expensive to fix. Keep in mind - I have heat now. While my furnace will eventually depreciate to the point it needs replacement, to do all of this for no added functionality would be to take a new car's worth of value and gamble I might save a little on energy costs over the next 15 years. It's a dead-weight loss for me - I'm not going to recoup that on a house sale. It's not my 'forever' home, so I'm probably not going to stay more than 5 more years. (US national tenure seems to be 10-13 years.)
- danmaz74 2y ago
  If that's possible for you, installing the heat pump so that it exchanges heat underground should improve performance a lot when the air is very cold (or very hot).
- Dylan16807 2y ago
  It's true that heat pumps have different performance characteristics from furnaces, but they weren't touching that issue, just insulation. Will insulation reduce your needs? Yes. If you get into a situation where your foundation is responsible for most of your heat loss in -10F weather, you're in a great situation! If improving the insulation on your walls is too hard, well that's disappointing, but that's a different topic from what happens when you do have good insulation.
  - 9x39 2y ago
    Unfortunately, it's not just apt install insulation (wouldn't that be nice?), its a multifaceted problem involving energy sources (especially if you're shutting one down), heating infrastructure, housing stock retrofits, money, and more money. The whole story about my house was just to try illustrating the difficulty of reducing a problem to "add insulation" and the downsides of ripping out otherwise-working infrastructure.
    - Dylan16807 2y ago
      Adding insulation has complications, but not as many as you're making it out to have. You're making it sound like adding insulation requires replacing your heating system, and it definitely doesn't. Making it just "add insulation" doesn't reduce the problem to trivial levels, but it does reduce the problem significantly.
- OfficeChad 2y ago
  [dead]

9x39 2y ago

That would make sense at first glance, but I was talking to my HVAC contractor and they warned me not to make that assumption. It's not easy to compare gas furnace BTUs to heat pump BTUs for both physics and issues specific to my home (and probably most homes not made in the last decade or so). It gets to -10F most winters here, but heat pumps struggle as it dips below freezing, while a gas furnace doesn't. What does that mean for heat in the colder parts of the year? Will I struggle to maintain 68F even if the BTUs are the same? This ties into my home design as well: Can I even substantially change my home's r-value the way it's built? I couldn't afford a new home when I bought my house, so I live in older housing stock - 1949, made heavily of cinder blocks with plaster and stucco around them. It didn't have ducting when built, and that was partially retrofitted in using a central furnace with limited air ducts to push heat clumsily from the center of the house into a few primary rooms using a California plenum to pull air from the foundation, connected to certain rooms through floor registers. There's no good way to fix any of these compromises short of ripping half the home apart, or just building a new one, so the least bad compromise is usually an over-specced central forced air solution. Do I get a central heat pump and air handler system with 100k peak BTUs? Do I get several mini-split units, each adding up to 100k BTUs? Do I overbuild on BTUs if I go mini-splits or multi-head? How will multiple smaller heat pumps work in winter as it freezes? Will insulating change that? I can't insulate my foundation more than the earth already does. I guess I could rip out all my plaster walls and put in drywall and high r-value insulation behind them, but at that point, maybe a new house would be more worth the effort. I think these kind of problems are endemic to the older housing stock and they're devilishly expensive to fix. Keep in mind - I have heat now. While my furnace will eventually depreciate to the point it needs replacement, to do all of this for no added functionality would be to take a new car's worth of value and gamble I might save a little on energy costs over the next 15 years. It's a dead-weight loss for me - I'm not going to recoup that on a house sale. It's not my 'forever' home, so I'm probably not going to stay more than 5 more years. (US national tenure seems to be 10-13 years.)

danmaz74 2y ago
If that's possible for you, installing the heat pump so that it exchanges heat underground should improve performance a lot when the air is very cold (or very hot).
Dylan16807 2y ago
It's true that heat pumps have different performance characteristics from furnaces, but they weren't touching that issue, just insulation. Will insulation reduce your needs? Yes. If you get into a situation where your foundation is responsible for most of your heat loss in -10F weather, you're in a great situation! If improving the insulation on your walls is too hard, well that's disappointing, but that's a different topic from what happens when you do have good insulation.
- 9x39 2y ago
  Unfortunately, it's not just apt install insulation (wouldn't that be nice?), its a multifaceted problem involving energy sources (especially if you're shutting one down), heating infrastructure, housing stock retrofits, money, and more money. The whole story about my house was just to try illustrating the difficulty of reducing a problem to "add insulation" and the downsides of ripping out otherwise-working infrastructure.
  - Dylan16807 2y ago
    Adding insulation has complications, but not as many as you're making it out to have. You're making it sound like adding insulation requires replacing your heating system, and it definitely doesn't. Making it just "add insulation" doesn't reduce the problem to trivial levels, but it does reduce the problem significantly.
OfficeChad 2y ago
[dead]