Do I need a large air conditioning vent in my crawlspace?

Question

The fan which circulates heat from my furnace in the winter and cool air from my air conditioner in the summer resides in the basement of my ranch home. Large rectangular ducting goes up from the unit to a height of about 6 feet off the floor of the basement and then extends horizontally about 8 feet out into my crawlspace where the metal ducting ends and transitions into many insulated circular ducts which lead to various rooms in the house. My question is, just before where the rectangular metal ducting ends is a HUGE grate on the underside of the duct which during the summer seems to do nothing but dump massive amounts of cold air directly into the crawlspace. Does having a grate in this location serve any important purpose? Can it be closed off/sealed to direct more air upstairs? When outside temperatures get above 85 degrees the air conditioner can't keep the upstairs a stable temperature but the basement will feel like its in the mid 60's.

Answer 1

Its difficult to understand exactly WHY the HVAC company placed it there, however, do not permanently seal it. Just try to temporarily block it and see what happens.
You could contact the installing HVAC company and ask for an explanation.

Answer 2

I am sure there must be a good reason for it, if you live in a hot climate your attic gets hot as hell and they may need to cool it down to keep the rest of the house balanced, there is a lot that goes into the balace equation, they have to bring in as much as goes out or they create a vacuum. I wouldn't close it off until you have an expert look at it. It may have been installed by someone who thought bigger is better aand realized afterword the problem with that is too much power for a small area means it is on and off all the time so they needed to dump some of the air.

Answer 3

Your set up is setting you up! This situation can cause condensation which will lead to black mold.

Contact a reputable heating and cooling technician for a consultation. It might cost you $65 to get an opinion but it will be worth it because black mold could cost you your health and/or home!

Good Luck!

(This happened to me by the way. I had them put a booster fan in the ducting and they changed the grate for the basement to a much smaller and easily controlled one.)

Answer 4

Some utilities offer a free inspection of heating and cooling systems, ask to see if yours does. I would understand if it was an intake, I would put in a shut off or a vent dampener.