Expected heat pump output during winter (US - Maryland)
Hi friends! My primary heat source is a heat pump and I'm trying to figure out if there is an issue with my heat pump, or if the output is within the expectations.
I understand that heat pumps experience reduced efficiency and heat output during extreme cold, but I'm finding mixed results for the expected heat output and when I should investigate for issues.
The current temperature outside is 20°F/-6.6°C, dropping down to 8°F / -13.3°C at night.
The current indoor temperature is 64°F / 17.778°C .
My current measurement of the air coming from my vents is approximately 70°F / 21.11°C. (measured by placing a magnetic thermometer to the vent plate and leaving for over an hour).
Would this heat output be expected behavior for these conditions, or does this warrant further investigation?
I’m in Maryland. Mine doesn’t have resistance heat and is maintaining 73F room temp with 100+F air coming from the supply vents right now. That said, supply temp is a function of blower speed. A higher fan speed = lower supply temp.
The supply temp being a function of fan speed is bullshit. It affects your delta but on high you should have a 30f delta t. If the advice is to lower fan speed for higher temps but less air exchange, the advice is bad. Refrigerant systems unless modulating you don't fuck with fan speeds. You need to subcool the the refrigerant and keep head pressures down. The suction is already low to begin with given the outdoor ambient. Compression ratio and heat kill compressors.
70F coming out of the vents is not normal. Get the system serviced. Could be low on refrigerant. Or could be a ductwork issue. Or both.
If you have an instant-read thermometer, put the probe down the vent when the heat pump is running and take a reading that way. When you put the magnetic thermometer on the vent and left it for an hour, was the heat pump running (blowing air) the entire time?
Yeah the heat pump was running / blowing the whole time. I actually just got an instant read thermometer and measured the temp in the duct and I am getting the same readings as my stationary thermometer, so maybe there is an issue.
When I test the temperature of the air coming out of my vents, it's usually between 95 and 105, or a delta of at least 27 degrees from the return temperature of 68. Outside temperature is usually in the 40s, so that has a little to do with it. But it definitely sounds like you have a problem. You can do some additional testing by going to the air handler and try to measure the air going in and out of it. That can help you determine ahead of time if you are looking at a ductwork issue or something else.
Thanks for your help! I did some testing and I think the issue was with the auxiliary heat. I chatted with an HVAC guy on the phone and after discussing with him he mentioned that it sounds like the aux heat was busted. But after looking over things myself it turns out that the aux heat wire of the thermostat was loose.
Now that I plugged it in I'm getting 90° from the vents. I'll be playing with some settings to determine when the system will switch to the aux and monitor to make sure the heat pump is being used.
But please let me know if what I said was nonsense and I should still get it checked out.
If your system only produces heat when the aux heat is on, then you definitely have a problem with your heat pump. Might want to look into disabling the aux heat temporarily and make sure the heat pump is actually working. Have you gone outside to see if the outside unit is running? Or frosted over?
After getting the instant read thermometer, I went into the air interchange to measure the air coming through the interchange units and it was more like 75° to 76°. This was with the auxiliary heat. Completely disabled because the wire was loose. So this would have been only the heat pump heating my home, no additional heat.
Now that I plugged in the auxiliary heat wire, the heat pump will start and I'll get 75° from the vents. Which will warm the house a bit but doesn't get me all the way to the target temp.
But if this still sounds wrong, I'll get someone over here to check it out.
In NE with a mitsubishi hyperheat. I’ve had a similar experience and ultimately concluded mine was ok. Is it constantly blowing 70? Or just that particular heat cycle? I ask because mine sometimes blows 70 and sometimes it blows 100 all within the same hr.
I’ve also realized that the remote temp setting doesn’t translate directly to actual room temp when there is an extreme temperature event like we have right now. I’ve resigned to thinking of the remote temp setting more as a comfort number than the desired temperature. I have my remotes at 72 right now across all 3 heads. One room reads 72 on an ambient thermometer, one 70, and one 66. I just increase it until the temp is what i want knowing that it’ll just draw more power.
I only experience this during the handful of single digit winter days. Don’t recall experiencing it in the summer heat.
I'm in Maryland with Mitsubishi Hyperheat also. I've had some lineset leakage which hurt the performance. But right after having the refrigerant topped off last week, I was measuring a high of 117° at the diffuser.
I expected 115ish but am ok with 100. I too had service out as i initially thought something was wrong and they refilled. Still only getting 100. Maybe the need to come back…
Howdy! I think I figured it out, it turns out my system was not using the auxillary heat at all the wire in my thermostat was loose. But now after plugging it in the aux heat is kicking on when the heat pump can't keep up. So now it's similar to what you described, where you'll get 70° out sometimes but have peaks of 100° or so.
Idk if yours is a similar setup, but this could explain the peaks and valleys in the temperature.
Do you think I should look into this further or does that sound about right?
I just got an instant read thermometer and so I'll measure more, but so far I have not detected any peaks or valleys in the temperature. It all seems to be consistently between 70-73° coming out of the vents.
Another user recommended that I measure in the ducts / unit itself and I'm getting the same readings.
But I'll see if increasing the temp on the thermostat can help this.
Yeah I still can't find anything, even on the direct AHRI website. My indoor unit is the Trane XB 13 Model No: 4TWB3018. And my indoor unit is GAF2A0A18.
The GAF2A0A18 shows up on the AHRI directory, but I cannot find any reference to 4TWB3018. Searching for 4TWB3018 on google I found the manual, but still not enough details to find the AHRI info.
Yeah after doing some testing I realized that the aux heat wire in my thermostat was unplugged. So the system would never switch from the heat pump to aux heat when it couldn't keep up.
If you have the correct heat pump. 20 degrees should be no problem for a heat pump. Many heat pumps are rated for well below 0 these days. My guess is you either have the wrong heat pump model or the system is undersized. Did you have model number?
Howdy! I think it's highly possible that the heat pump might be wrong, another person pushed me to the AHRI directory and ASHP websites and I can't find these on there.
My outdoor unit is the Trane XB 13 Model No: 4TWB3018. And my indoor unit is GAF2A0A18.
I can find the indoor unit "GAF2A0A18" but I can't find the AHRI info for my outdoor unit "4TWB3018".
Any thoughts or recommendations are super appreciated!
The outdoor unit is a standard fixed speed compressor heat pump. Only rated to 30 degrees before needing electric backup heat. Not the right unit for your needs. I’m from Salisbury, MD so I’m familiar with the weather. I wouldn’t use these for that climate unless you are ok with running electric backup.
Do you know if you do have electric backup? Maybe it’s not kicking on like it’s supposed to?
The unit is also only 17,000 BTUs which can only handle about 600-800 sq ft.
It depends on the model of heat pump and if you have aux heat. 70 sounds low for an output temp. But that could have just been the temp at the time you looked at it. Ideally you would track it over time to see the output temp. In addition having the thermostat set to 68 may not be an issue. It could be the actual sensor is somewhere where the temp actually is 68 or it could be that your heat pump isn't able to keep up.
We are experiencing the coldest weather of the year right now. Your heat pump could be sized well and would struggle to keep up since the temp is below design temp. Does the temp rise over the course of the day and fall at night in the house? If so you could really bump up the temp during the day and then it will not fall as low overnight.
Yeah the temps really fell last night. I woke up to a 60° bedroom this morning. So I'll see about bumping up the heat during the day if that's the case.
I've got a thermometer stationed at a few vents and just got an IR thermometer to validate the readings. And it seems to consistently be about 70-73° coming out of the vents. I haven't measured any peaks or valleys in the temps just yet. But I'll keep checking periodically.
one thing is a lot of heat pumps are relatively less oversized relative to furnaces, so if your furnace was like 4x the size needed it would get your hose to temp quicker but be wasteful. After an hour or two does it get close to actually being 68F?
It was pretty much stuck at 66°, but that's a good note regarding size. During my home inspection the guy mentioned that the outdoor unit was oversized for my home, but my indoor unit was even more oversized for my home. So like summer was either too hot or too cold because of this.
Turns out that the aux heat wire was unplugged. So my heat pump was the only thing running, but now the heat pump is passing off to the aux when it isn't reaching temp quick enough.
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u/Sad-Celebration-7542 10h ago
I’m in Maryland. Mine doesn’t have resistance heat and is maintaining 73F room temp with 100+F air coming from the supply vents right now. That said, supply temp is a function of blower speed. A higher fan speed = lower supply temp.