After foundation and roof work, condensation on registers

[kelt65]

Now what. After spending a lot of money on the foundation and roof, almost all my registers (for HVAC) are showing a lot of condensation, the condenser seems to be having a much more difficult time cooling the house, and now I'm seeing a little mold around the registers. What on earth could cause this?

The registers are in the ceiling and the ducts run through the attic. The roof was not vented until the other day when they added whirly things (2) to the top of the roof. They are spinning pretty fast. I do not have soffit vents but air from under the house does vent to the attic through the framing and because of restoration work there are several holes in walls and one ceiling hole which are now venting to the attic. They also pull in a great deal of outside air. I have been closing this part of the house away from the thermostat to minimize the damage to the power bill while the house is being torn up, that seemed to work ok but it did cost more. Should I close the registers in those rooms with holes? Will that cause other problems?

Obviously the condensation is because the register is colder than the humid air surrounding it, right? How the hell does that happen? I think I am sucking a LOT more conditioned air out of the house than I was before the roof was replaced. I am worried I am messing up my system by just running it. Right now I can't get the house below 79F and it is very humid and uncomfortable than it was before the roof was replaced.

Should I buy a portable, window exhaust unit to use temporarily while the house is being worked on? I imagine they are pretty hard to sell ... I guess I should at least get some think plastic and cover up all the holes? They're gonna be there at least another week or two ...

[shazapple]

It sounds like air from your basement (which would be high in moisture) is getting into the conditioned space and condensing where it is coolest (aka at the registers). Hopefully once renovations are done the basement will be sealed off a little better, but in the meantime a dehumidifier would be your best bet.

A roof needs an intake and an exhaust. If you just have the whirly exhaust then the air must be coming from somewhere (most likely the interior). The combination of exhaust only in the attic and holes in your ceiling/floor is probably causing the "chimney effect" and pulling the moist basement air into the rest of the house.

[kelt65]

It sounds like air from your basement (which would be high in moisture) is getting into the conditioned space and condensing where it is coolest (aka at the registers). Hopefully once renovations are done the basement will be sealed off a little better, but in the meantime a dehumidifier would be your best bet.

A roof needs an intake and an exhaust. If you just have the whirly exhaust then the air must be coming from somewhere (most likely the interior). The combination of exhaust only in the attic and holes in your ceiling/floor is probably causing the "chimney effect" and pulling the moist basement air into the rest of the house.

Thanks ...

No basement - just open crawlspace. It's all outside air!

The house does have intake vents for the attic, they're just not soffit vents ... the balloon framing provides quite a large channel from the crawlspace to the attic. There is a sort of soffit vent all along the eaves, but it's just a 2" gap open from the outside to the attic all along the sides of the house.

[kelt65]

Wouldn't it be a good idea to get a portable for the time being and keep the central condenser off? I am pretty much living in one room right now and sleeping in another. Are they easy to bring between rooms? They're $500 but if it save me that much over the duration of the renovations it will be well worth it. I'm thinking I will definitely need it in the next phase when i am living in the front (finished rooms) of the house and they are tearing up the rest.

[Gothichome]

Kelletim, any chance you've now made the home to tight. Free air circulation in and out of the house although controlled is part of how these old homes work.

[kelt65]

Kelletim, any chance you've now made the home to tight. Free air circulation in and out of the house although controlled is part of how these old homes work.

Why would it be too "tight"? I haven't even gotten to insulation yet .. it's a total sieve right now, with channels to the attic from the interior and the outside!

[Neighmond]

What, then, do we know for sure? We know that when hot atmosphere touches your artificially cold air ducts, there is condensation-it's the principle which drives mechanical dehumidification and water distillation both. It's why your terlet tank may sweat after flushing it on a hot day. We can draw from this and say that if you isolate your air ducts from the attic enough, they will be cold enough at the registers where the hot room air at the ceiling will condense on the cool metal and the artificially cooled ceiling surface adjacent.

Keeping air moving at ceiling level in the rooms is the first step. It will carry off the first droplets of condensate and warm the registers, along with breaking the stagnation that is known to occur just above head level and helps to keep the artificially cooled air in circulation, which means your system can work smarter and not harder.

So why notice it now? Here is my guess: When you had poor circulation in your attic the air passing through the ducts was already probably warmed enough by the stagnant sitting air in the attic that the temperature differential at the registers was not radical enough for condensation to occur. Now, with living air in the attic, the cool air is staying cool longer and making it to the registers, where the trouble soon begins.


Just some thoughts

Cheers!
Chaz

[shazapple]

No basement - just open crawlspace. It's all outside air!

The house does have intake vents for the attic, they're just not soffit vents ... the balloon framing provides quite a large channel from the crawlspace to the attic. There is a sort of soffit vent all along the eaves, but it's just a 2" gap open from the outside to the attic all along the sides of the house.

The crawlspace would still have high moisture, especially if you don't have a vapour barrier on the ground.

The high moisture or long run times wont damage your existing system. A portable unit may help you feel cooler but it won't solve the humidity issue. A dehumidifier would still be the best bet and is never a bad thing to have in an old house.

[kelt65]

No basement - just open crawlspace. It's all outside air!

The house does have intake vents for the attic, they're just not soffit vents ... the balloon framing provides quite a large channel from the crawlspace to the attic. There is a sort of soffit vent all along the eaves, but it's just a 2" gap open from the outside to the attic all along the sides of the house.

The crawlspace would still have high moisture, especially if you don't have a vapour barrier on the ground.

The high moisture or long run times wont damage your existing system. A portable unit may help you feel cooler but it won't solve the humidity issue. A dehumidifier would still be the best bet and is never a bad thing to have in an old house.

Yes I mean that the outside air is worse than bringing in basement air

[raine]

Find out what is the proper way to insulate the duct work in the Attic in your area. I would put the money there instead of a window unit if using the central air is what you intend on in the future.
Your new whirly vents and roof are probably fine but they are constantly bringing in humid air because you live in New Orleans.