4 ms·

I don’t think it’s normal for a heat pump to just stop working completely like that vs. just getting more and more inefficient. Wonder if perhaps it iced up and

I don’t think it’s normal for a heat pump to just stop working completely like that vs. just getting more and more inefficient. Wonder if perhaps it iced up and the defrost wasn’t working.

NDizzle 3y ago
It's my experience that they do stop working completely at some temp. The defrost cycle creeps up to 100% and there goes the heat.
- simonblack 3y ago
  That's because the heat-exchanger is not efficient enough to prevent too much frost from building up. The answer there is a better (probably bigger) heat-exchanger.
  - NDizzle 3y ago
    Yep, correct. As many have pointed out in this thread though, HVAC is full of trade offs. I COULD get a bigger heat exchanger.. Although my furnace is already a 5 ton unit. The question is, in the Ozarks, where I am, are the 1-4 days a year where it's too cold to run the heat pump worth paying the extra money for the larger system? I added an efficient wood stove instead. There's a good tax rebate that covers installation as well - I took advantage of that last year.
solardev 3y ago
It's entirely possible? Mitsubishi makes a bunch of different models, and ours is a cheaper one. Our area rarely gets under 0, so it's understandable why the landlords chose this model (and it's also an older model, for an older apartment). They have other models rated down to -15 or lower. But even if it's because the defroster stopped working, or it's just an auto-shutoff feature to keep the equipment safe... the end effect is the same: There is no more heat when you most need it, and you'll freeze. We were wrapped up in multiple layers that day and tried to warm the house however we could, but ended up just needing to stay with a friend cuz it was so cold. In some areas, "two sources of home heating" is mandated by law, but not where I live now. It still seems like good advice, specially if you can do that with two separate fuel sources (like electricity vs natural gas vs propane vs heating oil), in case one infrastructure goes down, as they often do during the worst storms.
timbit42 3y ago
My heat pump is 12 years old with a CoP of only 3 so when it gets down to -15C, it's less efficient than a resistive heater so it shuts off and the display shows P3. It was designed that way so you can have a secondary heat source set a few degrees below the temp you normally want so that kicks in when the heat pump shuts off. My backup is the electric baseboards I used before I got the heat pump. Some heat pumps have a resistive heater built into them which kicks in when it's too cold for the heat pump to have a CoP of greater than 1.

I don’t think it’s normal for a heat pump to just stop working completely like that vs. just getting more and more inefficient. Wonder if perhaps it iced up and the defrost wasn’t working.

NDizzle 3y ago

It's my experience that they do stop working completely at some temp. The defrost cycle creeps up to 100% and there goes the heat.

simonblack 3y ago
That's because the heat-exchanger is not efficient enough to prevent too much frost from building up. The answer there is a better (probably bigger) heat-exchanger.
- NDizzle 3y ago
  Yep, correct. As many have pointed out in this thread though, HVAC is full of trade offs. I COULD get a bigger heat exchanger.. Although my furnace is already a 5 ton unit. The question is, in the Ozarks, where I am, are the 1-4 days a year where it's too cold to run the heat pump worth paying the extra money for the larger system? I added an efficient wood stove instead. There's a good tax rebate that covers installation as well - I took advantage of that last year.

solardev 3y ago

It's entirely possible? Mitsubishi makes a bunch of different models, and ours is a cheaper one. Our area rarely gets under 0, so it's understandable why the landlords chose this model (and it's also an older model, for an older apartment). They have other models rated down to -15 or lower. But even if it's because the defroster stopped working, or it's just an auto-shutoff feature to keep the equipment safe... the end effect is the same: There is no more heat when you most need it, and you'll freeze. We were wrapped up in multiple layers that day and tried to warm the house however we could, but ended up just needing to stay with a friend cuz it was so cold. In some areas, "two sources of home heating" is mandated by law, but not where I live now. It still seems like good advice, specially if you can do that with two separate fuel sources (like electricity vs natural gas vs propane vs heating oil), in case one infrastructure goes down, as they often do during the worst storms.

timbit42 3y ago

My heat pump is 12 years old with a CoP of only 3 so when it gets down to -15C, it's less efficient than a resistive heater so it shuts off and the display shows P3. It was designed that way so you can have a secondary heat source set a few degrees below the temp you normally want so that kicks in when the heat pump shuts off. My backup is the electric baseboards I used before I got the heat pump. Some heat pumps have a resistive heater built into them which kicks in when it's too cold for the heat pump to have a CoP of greater than 1.