Hello, Our contractor conditioned our crawl space and for air flow in the crawl space, the crawl space air is connected to the intake on the HVAC. There is also a register elsewhere for air to flow back into the crawlspace. We had the crawl space conditioned based on recommendations of an energy audit (no moisture problems). Another contractor from our HVAC company said that this is unheard of - connecting crawlspace air to the intake duct of the HVAC. So I need advice as to is it ok to have the duct carrying the crawl space air be connected to the HVAC before the air goes through the air filter? Is this a health issue? The crawl space is empty and we have never put anything in it. Thank you very much. Respectfully, Chklio

do you have a radon pipe under the slab connected to a roof vent?

That setup depressurizes the crawl space when the HVAC runs and creates no airflow when it doesn't - not the best idea. Some better ones: a) seal up the crawlspace and put a low temp dehumidifier in there or b) get a pair of small duct fans and make one push air in and the other pull air out of the crawlspace (leaving it always pressure balanced and close to house interior humidity).

Hello Bob I -Thank you very much for your response. We do not have a radon pipe. I am in Maryland so radon is an issue, in general. The house was tested ok for radon about 25 years ago - but I don't know the extent of the testing (a few days or a whole year). The crawl space has a dirt floor which now sealed with plastic sheeting.

Hello jonr- Thank you very much for your response. The HVAC person who said that he had never heard of the set up such as ours suggested covering hole of the duct that takes puts the air into the HVAC from the crawl space with a register and placing a humidex in the crawl space. I don't have a moisture problem in the crawl space, from what I understand, the duct connecting crawlspace air to the intake duct of the HVAC was to move the air around in the crawl space and thereby keep the humidity in an acceptable range.

Is the method of introducing the crawlspace air to the intake duct of the HVAC an approved practice?
Will a humidex help in my situation?

Thank you again.
Respectfully,
Chklio

It's pretty common for sealed insulated-conditioned crawlspaces to be ventilate that way. The ventilation requirements of insulate sealed crawlspaces are quite low, and if the house is both heated and air conditioned, it should be enough to keep it sufficiently dehumidified and mold-free.

If the crawlspace is NOT insulated or the house is not air conditioned ventilating it with conditioned space air could conceivably carry some risks, but in most cases those risks would still be pretty small.

Why was it recommended by the energy auditor?

Hello Dana 1,
Thank you for your email. The energy auditor recommended that the crawl space be insulated based on the fact that the floors in the rooms above the crawl space were cold in the winter and you could always feel air movement in the den that is next to the crawlspace. The cold slight breeze in the den was coming from the direction of the crawl space in winter.

The HVAC person, who said that he had never seen a set up such as ours where crawl space air was being conditioned by being sucked into the HVAC before the filter, said there could be health concerns. He recommended that the duct where the crawl space is being brought into the HVAC be replaced by a register. And in order to control humidity, he recommended the humidex. But the humidex would have to be vented to the outdoors and this ruins sealed conditioned space concept. Is this correct?

Are there any health issues that I need to be concerned about with the fact that air from the crawl space is going through the HVAC and into the house air?

Thank you again.
Respectfully,
Chklio

Are the crawlspace walls air-sealed and insulated?

Is there a ground vapor-retarder &/or slab on the floor of the crawlspace?

Chklio,
we have done un-vented insulated crawlspaces before:
with waterproofed block walls, insulated with foil backed foam insulation over block walls , 6 mil vapor barrier covered with a 2" rat slab
the entire crawlspace was used as a return air plenum
the slab was sloped to one central point with a sump hole just in case a sump pump was ever needed

Hello Dana 1
Thank you again for your email. The crawlspace walls are air sealed and insulated and the dirt floor has sealed plastic sheeting.

Hello cmkavala,
Thank you for your email. So it is good to know that it is not unusual that the air from the crawl space is being sucked into the HVAC and distributed through out the house.

Thank you both again.