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Old 09-20-2021, 04:36 AM   #1
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Heat pumps and humidity

Current weather where I am traveling has it warm and sunny enough during the day to run the AC, and low 60’s at night, so nice to turn on the heat in the morning to bump the inside temp up a bit.

What I notice when the ceiling heat pumps (part of the AC units) start up is that they seem to pump out a LOT of humidity. Where is this coming from? Is it residual condensate water remaining from the AC units running late the day before?
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Old 09-20-2021, 04:39 AM   #2
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Wet evaporator coil getting heated up. Got to go somewhere.
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Old 09-20-2021, 05:18 AM   #3
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I kind of figured it was something like that. Took me a little by surprised though… condensed all over the side windows and windshield!
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Old 09-20-2021, 06:11 AM   #4
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There shouldn't be that much moisture added to the inside of the RV. Check to see if all of the water generated by running the air conditioner is draining out of the roof units and not left standing in the air conditioner. All in all, if there isn't any standing water, the heat pump, or propane furnace for that matter, does not produce any additional moisture.

I think what you are seeing in the morning when you heat the interior, is the now warmed humid air, is in contact and condensing on the cool/cold window glass. The humidity is probably coming from your breathing collected over night due to the windows being closed.
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Old 09-20-2021, 10:10 AM   #5
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People always find it counterintuitive, but open a vent or window a few inches when running any heat source, such as furnace, HP or stove top. It will reduce the moisture issues. It took me years to believe it myself. We would camp at Yosemite every Thanksgiving and keep everything all closed up.....the windshield would be sopping wet in the morning. Once we started leaving a roof vent pen several inches, problem solved.
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Old 09-20-2021, 10:20 AM   #6
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Originally Posted by MN_Traveler View Post
I kind of figured it was something like that. Took me a little by surprised though… condensed all over the side windows and windshield!
So, your talking inside your coach?

I've never experienced that running a heat pump.
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Old 09-20-2021, 06:36 PM   #7
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Vacuuming drain ports or hoses are a good idea. But...If the evap coil is soaking wet from the AC dehumidifying, the next morning running as heat pump, water left on coil would start to be a humidifier for a bit. Finish running just the fan for a while later in day may help in the morning. Relatively the same amount of humidity would end up in coach but not be all warm wet air pouring out of vents in the morning. Assuming your switching from heat to AC you may also want to run the ACs a bit harder or longer to dehumidify the coach better during the day to bring down humdity. Other stuff like hang/lay bath towels outside to dry or pop in dryer , squeegee shower walls down ect. might help as well.
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heat, heat pump, pump

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