Humidity at night on cooler/humid days

[Anonymous]

The humidity in my house at night these past couple of days goes up to 70% upstairs at night. Even set to 69 all day, my AC shuts off at night because it’s very cool but then humidity rises from mid-high 50s during the day to 70 at night. Downstairs it goes to 62. Is there anyway to deal with this without forcing the Ac to run at like 66 temp?

[Anonymous]

Newer multi-speed heat pumps handle this by running at a lower rate to dehumidify. This may also happen when (and this happens a lot!) HVAC companies replace equipment and install too large of a unit, so they short cycle (run for a short duration and reach the set point for temperature but do not remove the humidity). This is a chronic problem. One way to help, short of replacing with more recent equipment, is to get a dehumidifier, if you have a place to set it. It will work independently to remove moisture.

[Anonymous]

Mine is reading 55% right now and I have had the a/c set to 72. So your hvac is probably oversized.

If it’s only in cool, humid weather I would just not worry about it. It won’t cause any problems for a few days.

[Anonymous]

Are you running a dehumidifier? I’m constantly amazed at how much water is pulled out daily.

[Anonymous]

The poster who mentioned the importance of correct unit sizing is on the money. Our new system is actually smaller than the one it replaced and the humidity levels are so much better. Simple option is to just run a dehumidifier.

[Anonymous]

Anonymous wrote:The poster who mentioned the importance of correct unit sizing is on the money. Our new system is actually smaller than the one it replaced and the humidity levels are so much better. Simple option is to just run a dehumidifier.

Did your installer do a “manual j” calculation?

We’re trying to find someone that actually performs this calculation. Apparently it’s required in Fairfax Co when you replace your system but we can’t find a contractor who does this!

[Anonymous]

Anonymous wrote:

Anonymous wrote:The poster who mentioned the importance of correct unit sizing is on the money. Our new system is actually smaller than the one it replaced and the humidity levels are so much better. Simple option is to just run a dehumidifier.

Did your installer do a “manual j” calculation?

We’re trying to find someone that actually performs this calculation. Apparently it’s required in Fairfax Co when you replace your system but we can’t find a contractor who does this!

I’m not sure what type of calculation they did, sorry. I just remember the estimator saying the old unit was oversized.

[Anonymous]

It's not just the size of the unit it's whether it has multiple/variable speeds. The way our HVAC tech explained it is this: we have a 2 ton unit for our upstairs, which is poorly insulated. On the cooler humid days, it runs at a very low speed, essentially mimicking a 1/2 or 1-ton unit. Still dehumidifies well but doesn't put as much cooling effort in when it's not needed. Variable speed is essential in our climate.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:The poster who mentioned the importance of correct unit sizing is on the money. Our new system is actually smaller than the one it replaced and the humidity levels are so much better. Simple option is to just run a dehumidifier.

Did your installer do a “manual j” calculation?

We’re trying to find someone that actually performs this calculation. Apparently it’s required in Fairfax Co when you replace your system but we can’t find a contractor who does this!

I’m not sure what type of calculation they did, sorry. I just remember the estimator saying the old unit was oversized.

No one runs a manual j and the county staff who review the plans also don’t know how to run it. Most hvac installer these days can’t read or write English so performing a load calc via manual
J would be a bit of stretch, shall I say? The county requires it, they fabricate it, the county staff then rubber stamps it (literally).