posted earlier issue inre to damp new house. Received many helpful responses. Much appreciated. Since then, HVAC man took out downstairs unit (coil and other stuff) from under the house and replaced the outside unit as well, at no cost. Old unit was said to be oversized. Was a 4 ton now have a 3 ton. After two or three days the indoor humidity will get into the high fifties at which time I turn an indoor dehumidifier which makes it okay again.
He now says the new system is working fine and the problem is crawl humidity. He says water vapor is escaping from under the vapor barrier into the air and migrating through the flooring into the house. The vapor barrier is not sealed at the perimeter nor sealed along the continuous center footer running the length of the house. The vapor barrier is intact and abuts the footer all the way around but is not sealed. No evidence of any moisture under the vapor barrier at all.
Questions.
What should be the desired summer humidity range for a crawl in KY, with no drainage issues?
If I seal the entire perimeter and the continuous footer, what is the best way to seal the plastic VB to the concrete block wall and where the two pieces of VB meet?
What type of professional could assess the situation and give me independent advice?
Replies
Hmmm, I don't recall if anyone mentioned an oversized A/C as a possible problem in the last thread, but, yeah, an oversized A/C results in a cold clammy house because of insufficient dehumidification.
I'm wondering if 3 tons is too big, as well. Only way to know for sure is run the heating calcs.
In my area (NW Ohio) you don't need to seal the VB, overlapped is sufficient.
Pull back a section and compare the moisture dryness of the soil at the edges and towards the center of a section of VB. If there is no noticeable difference, not much moisture is escaping around the edges. If it is distinctly dryer at the edges, then maybe there is a vapor problem. (I'm betting no.
I'd call around to local home inspectors, looking for one who (i) routinely (or at least often) takes moisture meter readings in crawl spaces and (ii) can think, and (iii) has 4+ years (>1000 inspections) experience.
I could tell you what I expect to find in crawls in my area, but that wouldn't help you in your area.
As with any problem, you want someone who deals with those problems every day. No one sees and specifically looks at crawl moisture issues more regularly than HI's
Fighting Ignorance since 1967
It's taking way longer than we thought
Bob, I still think it is likly the HVAC since your crawl is dry. A far out; but I once saw one that had standing water in the duct work. Can't remember how it got there but seem to rember the ducts were under a slab. That one would make you clammy all year round.
By the way, I can't remember have you tried putting the furnace/AC blower on continuous for a few days.
Edited 8/24/2006 10:35 pm ET by jimcco
it has a variable speed motor and fan runs constantly
How much of the time is the unit running? Short run times reduce the dehumidification provided by the AC.
Do you run the fan continuously? If you do it will re-evaporate moisture of the wet coil back into the space after the condenser shuts off.
Do you have a vented attic with ac and ducts in it?
What are your average outdoor dewpoints?
Do you use your bath vents when showering?
Is your crawlspace vented?
Have you checked the moisture content of the lumber in the floors and walls?
crawl has vents but they are closed which has negated the condensation on the metal pieces where the supply lines enter the house.
No apparent moisture anywhere now
attic isnt an issue because it is a story and half upstairs is fine
use shower exhausts religiously
don't know the dew points, but it is really humid most days here in ky
The attic probably is an issue. Is it vented and does the ac equipment and or duct system reside there? There may be several issues but one that I see regularly is one that is caused by air conditioning systems that are located in vented attics or crawl spaces. Here's the short version.
The ducts and equipment leak, mostly on the supply side. Air that leaks from a supply duct into a vented space is basicly air that is being pumped out of the living space. This creates a negative pressure in the living space which draws air in from where ever leaks can be found into the envelope. If the air outside is humid(high dewpoint) then the humidity level in the building will rise. In summary, a home with ducts or equipment in a vented attic or crawlspace will experience negative pressures. Your house will suck. The attic can promote moisture infiltation in whatever part of the house has the greatest amount of air leakage. That will not necessarily be upstairs.
Running the fan continously will increase this effect. Running your fan continuously will also re-evaporate the water that is on the coil instead of letting it drain off to the exterior. This will increase interior moisture levels. In the winter this can also lead to excessive drying of the interior space in cold weather.(low dewpoints)
Fan coils should have a large delta across them in order to remove moisture through condensation. Get a thermometer and check the temperature in the return grill and in the supply grill. If the difference is less than around 18 degrees, moisture removal will be minimal. This can be increased by reducing the fan speed in order to increase the deltaT and maximize moisture removal.
the upstairs unit and ductwork in the 1.5 story home is in the attic. The downstairs unit and ductwork is in the crawl. The roof has continous ridge vent and vented soffits along all eaves. The attic has two electric exhaust fans (1) over the 3car garage/down and bonus room/above and (2nd) in the main attic. They are thermostatically controlled.
The crawl is vented but because of high humidity I have the vents shut which has negated the condensation on the crawl.
Unplug the attic exhaust fans and set the HVAC fans to auto so they don't run continuously and let me know how the humidity levels are affected.
Are these heat pumps?
upstairs heat pump downstairs, heat pump with gas backup. Will try it with the fans off.
Is the unit in the unvented crawlspace a direct vent model or will you have to re-open the vents in the winter time to provide combustion air?
how do you check the moisture in the wood floors and walls?
A pad type moisture meter can check the moisture levels. New homes often have huge amounts of construction moisture in them and it can take a long time to dry them out.
As far as sealing the poly to the concrete blaock wall and for the seams, use acoustical sealant. Sticks to everything and stays somewhat floxible so it doesn't dry up and crack or peel off.
Comes in big tubes.