Humidity

[ampulman]

My a/c is putting out about 9 lbs. of water per hour of run time. Despite this, the indoor humidity hovers around 50% (has ranged 48 - 53, but mostly 50+).

This A.M., measured the humiity in the basement and found it to be over 70%. The temperature was in the low 60s.

I know about stack effect and will have to wait for a cool spell to check the attic, but disregarding that, what other areas can I check?

Windows are double-pane, air tight; outside wall outlets are sealed. Is the sole plate (terminology?) a source of infiltration?

Would a minimal stack effect be sufficient to cause cool/humid basement air to rise into the conditioned area?

All suggestions welcomed. Thanks.

AM

[beenthere]

Yes.
Plus if your duct is in the basement, and your return leaks, you pick up humidity from that.

[ampulman]

Yes.
Plus if your duct is in the basement, and your return leaks, you pick up humidity from that.

Thanks, Been. Had done a check of the basement ductwork some months ago. Found some supply leaks and corrected a few leaks in the panning. Will go back and look over the return system again.

Also, I think a dehumidifier for the basement is in order. Thoughts?

AM

[beenthere]

It will probably make a world of difference in your comfort.

[paul42]

Windows are double-pane, air tight; outside wall outlets are sealed. Is the sole plate (terminology?) a source of infiltration?

AM

It is a fallacy to only seal the outside wall outlets. There is a lot of air leakage to the attic from interior outlets and switches as well. The leakage from each one is small, but they add up.

Any penetration through the ceiling drywall also needs to be sealed - lights, smoke detectors, etc...

The sole plate is just one of many sources of infiltration. Drywall is a good air tight barrier - except for all of the electrical work, and where it meets the floor, doors, windows, etc... - again, not just on the outside walls.

Drywall is very flat. Wood framing isn't. Join the two and you have many cracks and crevices for air to leak past. On exterior and interior walls, any opening at all through the drywall is probably a source of infiltration to the attic.

[teddy bear]

This the classic Midwest-Atlantic States problem. The amount of moisture your a/c removes indicates a good functioning a/c. The moisture sources are infiltrating outside air, the occupants, and diffusion of moisture from outside through the structure to the inside. I am posting the data from a WI home. Currently, 30-50 lbs. of moisture is removes per day. This is the amount moisture removal to maintain 50%RH in basement/home with moderater fresh air infiltration. This home should have 50-75 cfm of mechanical fresh air ventilation, when the home is occupied. The amount of natural fresh air is estimated at 0-75 cfm depending on wind. At 9 lbs. per hour, your a/c needs to operate 5-8 hours per day.
The graph I am posting has the VS fan operating continuously, a 90 pint free-standing Santa Fe Advance dehu in the basement set at 50%RH. The unit operates half time or $15/month. Operating the fan will warm up the basement and help cool the home. When the home gets hot enough to need real cooling (6-8 hrs/day), the a/c should keep the basement dry enough to need much dehu operation. Cool evening and wet days will raise the %RH enough to need dehumidification. Some on this forum think a/c should handle this problem. The fix is thought to eliminate fresh air infiltration. You need 50-75 cfm of fresh air to purge indoor pollutants and renew oxygen when people are in the home. The moisture contents in the fresh air during typical three seasons is approximately 30-70 lbs. of moisture per day.
Check my past posts for more info or post questions. Regards TB

[Shophound]

Thanks, Been. Had done a check of the basement ductwork some months ago. Found some supply leaks and corrected a few leaks in the panning. Will go back and look over the return system again.

Also, I think a dehumidifier for the basement is in order. Thoughts?

AM

The leaks in the panning....was it on the return side or supply?

If on return, is only the bottom of the joists panned, with the rest merely joists and subfloor, or is the entire chase lined/panned?

Panned joists/studs can be notorious leakers.

Sounds like you're drawing high humidity basement air into your return air side. A dehumidifier for the basement may be in order, along with good sealing of the ductwork.

[ampulman]

The leaks in the panning....was it on the return side or supply?

If on return, is only the bottom of the joists panned, with the rest merely joists and subfloor, or is the entire chase lined/panned?

Panned joists/studs can be notorious leakers.

Sounds like you're drawing high humidity basement air into your return air side. A dehumidifier for the basement may be in order, along with good sealing of the ductwork.

I wasn't aware that supplies were panned; thought only returns. The returns are panned and consist of joists & subfloor, only. Sealing will be high priority.

AM

[ampulman]

It is a fallacy to only seal the outside wall outlets. There is a lot of air leakage to the attic from interior outlets and switches as well. The leakage from each one is small, but they add up.

Any penetration through the ceiling drywall also needs to be sealed - lights, smoke detectors, etc...

The sole plate is just one of many sources of infiltration. Drywall is a good air tight barrier - except for all of the electrical work, and where it meets the floor, doors, windows, etc... - again, not just on the outside walls.

Drywall is very flat. Wood framing isn't. Join the two and you have many cracks and crevices for air to leak past. On exterior and interior walls, any opening at all through the drywall is probably a source of infiltration to the attic.

Thanks, Paul. Points well taken. While I was on the scene daily, during the construction of my home, there was a limit as to what I personally could do to make things better. I did note some air spaces where wires penetrated. Will have to check that out as well as interior partition walls.

The builder was kind enough to allow me to add foam in insulation around all of the window frames, before the drywall was installed. The insulation contractors left plenty of gaps and air spaces with their fiberglass. As a result, I can lay the palm of my hand on the drywall next to the window frame and feel absolutely no cold.

AM

[Shophound]

I wasn't aware that supplies were panned; thought only returns. The returns are panned and consist of joists & subfloor, only. Sealing will be high priority.

AM

Brain fart...of course we're talking returns...

...but ya never know, if the Wall of Shame is any indication of what can be done to an installation!

[House]

I cringe when I see the words "basement return air leakage". That
can cause a backdraft for a flued water heater if one is also in the
basement.

If you have no supply or return registers in the basement and also have
a door to the basement, you can check for a draft along the door undercut
when the blower is running and door closed.

Does the temperature in the basement change when the system is running?

[ampulman]

I cringe when I see the words "basement return air leakage". That
can cause a backdraft for a flued water heater if one is also in the
basement.

If you have no supply or return registers in the basement and also have
a door to the basement, you can check for a draft along the door undercut
when the blower is running and door closed.

There are no registers; I'll try it.

Does the temperature in the basement change when the system is running?

I have been monitoring humidity (wet bulb/dry bulb) but haven't watched temperature over duration of runs. I will look at that, but feel that will not be the case.

AM