To lower humidity, set fan to "ON" or "AUTO"?

[dan sw fl]

The main air return is about 72 at the end of the cooling cycle,
humidity about 62%.

I didn't get 50-55F at the register and 80-90% humidity.

I had the meter placed about 6 inches away from the register.
Was I not placing it close enough?

Good hygrometer needs to be practically placed "in the duct" close the the air handler.

Set T'stat to 77'F may decrease RH to 49 - 53% on a hot day.

One will never consistently achieve < 50% RH at 72'F with 2-stage unit
without VERY LOW air flow rate.
Coil must maintain less than 52'F dew point (ADP).

[Dr Gaius Baltar]

My temperature reader doesn't have probes that I can put in the register, it's one of these:
http://www.amazon.com/AcuRite-613-In...erature+reader

[beenthere]

Place it against the register.

[Dr Gaius Baltar]

Okay, I placed the temp reader up against the register. Here are my findings:

nearest register to furnace: after AC ran 23 minutes, 88% humidity, 64F
farthest register from furnace: after AC ran 20 minutes, 85% humidity, 64F

The temperature is 84 outside, 61% humidity, still 73 inside the house at the thermostat, AC still set at 73 and fan on AUTO.

[beenthere]

Coil not cold enough, or your return is drawing in unconditioned air.

[beenthere]

Look around the air handler and see if you see any openings in the return duct.

[Dr Gaius Baltar]

I wasn't sure which one of these pipes is the return air duct, so I took a picture to show you what I mean. If that's the correct duct (the big metal pipe with the red line pointing to it, with the white paintish stuff around it), then I don't really see any holes in it.

I can feel some air coming out of the lines that I indicated at the bottom of the picture, and in the bottom right I have magnified that area to show it in detail. Is that normal?

Does that white pipe coming out of the coil (I think that's the coil) look right, or does it look problematic? It leads to the outside, where it drains onto the grass.

[ga-hvac-tech]

Coil not cold enough, or your return is drawing in unconditioned air.

X2...

When the tech comes out, have him lower the fan speed a bit... Meanwhile, examine the entire return ducting as best you can for any cracks or loose joints. You can have the installing co repair them, or you can buy a roll of foil tape at the local hardware store and add some 'sweat equity' to your home. An aid to finding leaks in a duct system is to stick a really bright lite inside the duct, then examine it from the outside. Keep moving that lite along the duct and examining the outside. One thing I find on many installs: The filter holder door is loose and/or has cracks one can stick things through... Get yourself a roll of painter's masking tape--every time you change the filter, seal up the cracks. You would be amazed how small a crack will raise the RH in a home 10% or more.

[ga-hvac-tech]

I wasn't sure which one of these pipes is the return air duct, so I took a picture to show you what I mean. If that's the correct duct (the big metal pipe with the red line pointing to it, with the white paintish stuff around it), then I don't really see any holes in it.

I can feel some air coming out of the lines that I indicated at the bottom of the picture, and in the bottom right I have magnified that area to show it in detail. Is that normal?

Does that white pipe coming out of the coil (I think that's the coil) look right, or does it look problematic? It leads to the outside, where it drains onto the grass.

The white pipe is the condensate drain, it looks fine in the picture. Important thing there is a good slope and water flowing freely!
Yes, the box on top of the furnace is the coil. Is it level or sloping just a tiny amount forward? If it is sloping backwards, or away from the drain, that is not a good thing.
The rectangular metal box going down to the bottom left of the furnace is the return. Best if every crack and nook and hole is filled.
The holes with the copper lines on the coil are not a big deal, they are letting conditioned (heated or cooled) air into your utility room.

[beenthere]

The pipe the red line runs to is a return duct. but you have other returns. need to check them all.

[teddy bear]

Okay, I placed the temp reader up against the register. Here are my findings:

nearest register to furnace: after AC ran 23 minutes, 88% humidity, 64F
farthest register from furnace: after AC ran 20 minutes, 85% humidity, 64F

The temperature is 84 outside, 61% humidity, still 73 inside the house at the thermostat, AC still set at 73 and fan on AUTO.

With 73^F return, a we would need a <50^F dew point supply air. 64^F, 85% RH is 58^F dew point. Estimate a 50-53^^F coil temp, lower the air flow through the cooling coil to get a 45^F coil temp. This would lower the supply air to 55^F, 85%RH, a 51^F dew point. Slower fan speed or a more restrictive air filter will slow the air flow. During high cooling loads, this should provide 50%RH at 73^F. If not slow air flow more yet. This lengthens the cooling cycle. Fan "auto". during low/no cooling loads, a small whole house dehumidifier will maintain <50%RH.
Help us train your a/c tech.
Regards TB

[Dr Gaius Baltar]

The white pipe has a downward slope and the coil box appears to be level. Outside there are little tiny pools of water popping up on the grass where the drain pipe is draining water/coolant or whatever that substance is.

It doesn't seem like there are any leaks on the return, but it's cramped and I can't really get a good look at it. The only place that seems to have any air coming out of it is near the copper lines that I talked about earlier. From what I can access, anyway.

Teddy Bear, that sounds good, I will definitely ask again for the tech to adjust the fan speed or ramp profile when he shows up again.

[energy star]

The return is so close to that gas hot water heater. You should clean up any chemicals/paint/cleaning products from around the furnace

[Dr Gaius Baltar]

That's also the laundry room though, so I keep detergent there.

[vstech]

it's very hard to tell from your picture...

the pipe you have the red line drawn on does not appear to be the return. it looks like the supply. is there more ductwork under the picture you inset? is there ducts in the wall on the right of the furnace?

to me, it looks like the coil is loosely connected to a transition that turns, and then connects to a plenum that goes through the floor? can you tell if it's connected to the bottom of the furnace?

I'm guessing this is in your basement, so the duct HAS to be the return, but it looks like the supply is connected directly to it... maybe the installers panned the floor joists, and they just tied everything together on the outside?

can you shoot some more angles, and post better pictures?

[dan sw fl]

Okay, I placed the temp reader up against the register. Here are my findings:

nearest register to furnace: after AC ran 23 minutes, 88% humidity, 64F
farthest register from furnace: after AC ran 20 minutes, 85% humidity, 64F

The temperature is 84 outside, 61% humidity, still 73 inside the house at the thermostat, AC still set at 73 and fan on AUTO.

64'F (dT =9) is so EXTREMELY POOR, I cannot imagine what's going on.
System seems to be ~50% efficiency IMO.

[Dr Gaius Baltar]

The AC tech didn't come today because, for unrelated reasons, today was pandemonium. On Saturday a car ran a red light and slammed into us, but we are physically uninjured. The car is in rehab. Today, though, dealing with the claims adjusters about liability, that was really scary.

Head Six is gone, though. I think the force of the collision knocked the cylon chip in my brain around. My days of having half-naked ladies that nobody else can see appear before me are gone, I think. The car accident killed Head Six

Hopefully tomorrow there will be no insurance emergencies and I can go back to getting that tech to fix the humidity!

[Shophound]

Glad you're okay. Six will resurrect. Maybe she will tap into your a/c to get it working like a champ.

[Dr Gaius Baltar]

The tech came today and adjusted the ramp profile and my humidity issue is now resolved. After the AC has been on a for a while, the humidity drops down to around 50%. Before it was fixed, it was stable at 65%. The temperature of the air in the ducts right at the top of the furnace was about 51F when the tech last checked it (post-fixing), and 55F in the register in the master bedroom when I last checked it with my refrigerator thermometer. Looks like everything is good now!

I have reset the thermostat back to 75 (fan AUTO) and will see if I can nudge it up to 76, 77 or even 78 over the coming days while still feeling comfortable, due to the newly reduced humidity.

[Dr Gaius Baltar]

By the way, my HVAC guy recommended that I put in an Aprilaire 760 whole house humidifier. I could have gotten it at a discount if I had bought it when I got the whole HVAC system, but now it will be more expensive. He said that it should reduce my energy needs during the winter, because I'll feel comfortable at lower thermostat temperatures. I usually set my thermostat to 66 in the winter and wear socks and a second shirt to keep out the cold. I don't seem to get any sort of skin or throat irritation from the low humidity that we have now in the winter, around 20%.

I plan to live in this house for another 5 years. Do you suppose it would be cost effective to get this humidifier? Would it pay for itself in reduced heating bills?