Humidity in New Construction

I just moved into a newly built home in hot and humid atlanta. We have 2 main floors and a finished basement which sits mostly above grade. We have several digital humidity guages and all the floors have humidity in the mid to high 60's. The A/C works fine for cooling and is able to keep the house in the low 70's even when the outside air is 95+.

My question is what is a minimal acceptable standard for indoor humidity. My warranty book states that the a/c shall be capable of "maintaining summer design conditions as specified in the ASHRAE handbook"

I've done a bit of research, but can't come to a definitive conclusion on humidity standards given all the revisions and addendum to the ASHRAE handbook.

I obviously need to get the humidity down, but do the builder and HVAC folks have some responsibility to?

thanks in advance for the help.

 

60's% is high. Ideal should be around 40 to 50%. mine Avg about 41%.

On your hottest day, does your system run all the time, or cycles on and off?

if it cycles on the hottest time of the day, how long does it run?

brand/model of equipement?

My guts are telling me you have an over sized equipment.


FYI, new home will have high humidity for a while.

 

Jay,

Thanks for the quick reply.

The system tends to run off and on. For instance, today is 92 degrees, 51% humidity outside, and inside is 75 degrees with 62% humidity. The air only runs for a few minutes (10 minutes?) at a time.


For the two main floors there are three units. a carrier 3 ton downstairs (38ckc036), a 2.5 and 1.5 upstairs (38ckc030, 38ckc018). The total area is about 5000 sq ft. The basement has a separate 2.5 ton unit.

Are there any official standards in building codes or the ASHREA handbook regarding acceptable humidity. I know from a practical point of view, less than 50% humidity is comfortable, but are there any official standards.

 

http://www.sycorp.ca/iaqbc/newsletters/news3.pdf#search='ASHRAE%20humidity%20guideline' is the only thing that I could find..

10 at the most? wow.. that's short.

on our hot days, mine will run for hours and keep the temp. That's a right sized system.

What do you set for temp setting on this? All have it's own t-stat?

What's your furnace model?

 

Jay,
I take back what I said. Saturday was not typical as I think the thermostat was moved up and down.

On sunday, the downstairs a/c stayed on fairly constantly with an inside temp of 75 and outside in the high 80's low 90's. Still, though, the humidity did not drop below 60.

My furnace models are 3 carrier 58sta070-12 and one 58sta045-08.

Given that the a/c is running, should I expect the humidity to be lower. I know that i'm in humid georgia and this is new construction, but the humidity seems excessive.

I spoke briefly with the HVAC installers. They mentioned installing a in-line dehumidifier (april-aire) and I've also seen standalone units like the santa-fe.

any thoughts?
thanks,

 

Ok, you got the standard blower system.

Do you know what speed the blower is set at? If it's on the highest speed, you can drop the speed down one more..

Slower air flow will help remove the humidity.

On my furnace, I have the variable speed, can the blower runs on a slower speed to remove the humidity, after 10 min, it will speed up.

 

Jay,

just an update - I turned down the blower speed all the way and seem to have the humidity under control (mid 50's). Alternatively, the humidity has just dropped recently, and I won't know until next summer!

thanks,
nishan

 

if you dropped your blower at the lowest speed, you better keep an eye on the coil if you don't have TXV on it. it may freeze up on you.

On system with variable speed blower and TXV, they are able to get by with lower blower speed.

 

Id say you are trying to go to fast on this new home. It takes more than 1 year for a home to start to dry out. most of the time a winter with the heat on sure helps. Thats like most of the time a new home dont need a humidifier on it till the next year.

ED

 

Oversized sytems run short cycles and not long enough to remove humidity from interior of home. Make sure you have the right size system. Humidity needs to be maintained between 35-55% (measure with hyrogmeter sold where they sell thermometers). Dehumidifiers can be used to reduce humidity and fans to improve air circulation in order to minimize mold and mildew problems.