Two home HVAC questions

1)My basement is much colder then any other part of my house. Would it be okay to put a hole in the return ductwork in the basement? (Not a hole, per se, but a vent that could be opened in summer and closed/sealed in summer). It seems logical, when the AC is on, it wouldn’t have to work as hard to get the rest of the house down to temp, and if just the fan is on, it would bring some of the cold air up from the basement. The only reason I ask is becuase there isn’t one to begin with and it seems like such a good idea, there must be a reason not to.

2)Our furnace has a ''fresh air intake." A insulated tube that runs from out side the house along the ceiling of the basement and into a cold air return. My understanding is that it’s there to bring fresh air into the house. But it always seemed like a waste of money. In winter the furnace is trying to heat up freezing cold outside air and in summer it’s trying to cool/dry hot/damp air. Is that really neccessary? Can it be removed? (if it can, the resulting hole would be nice for question 1), or at least could it be pinched down a bit so it doesn’t bring in as much fresh air?

Both very good questions, and both questions I would ask of a HVAC professional, your life may be at stake. Your first idea seems innocent enough, but I would check. Your second idea sounds dangerous. Limiting any intake also limits exhaust and could prevent the expulsion of monoxide. In some systems, such as the one in my home the heat and AC are so tied together I would not chance a guess. I would leave it to the pro’s. At least that way your estate will know who to sue…

Limiting the fresh air intake (the one that connects to the return) should not limit exhaust. The air air to be combusted comes from a separete intake usually located near the exhaust pipe. Besides, my thought is that removing that altogether, or closing it off alittle will just force the system to use more inside air.
I assume it’s just a code that the goverment wrote. Even in professional kitchens now, you have to have a fresh air intake to replace the air the hoods remove.

The first thing though, just seems like common sense.

I am 14 years out of the field now and responding from memory but:
The Basement idea will not make a significant difference and may introduce more molds into the air system. Additionally you will be pulling less air from the main level, which will decrease overall airflow and might be counter-productive.

The Fresh air intake should be kept clean and open.
IRC: the main problem with not pulling fresh air is with SBS (Sick Building Syndrome) not Carbon Monoxide problems, but some systems might vary.

I haven’t read a single HVAC periodical in 14 year so I am far from expert at this point.


On pulling return air from your basement: Only if the basement is generally open to the rest of your home, or if it already has a supply air duct installed. If the basement is relatively sealed off from the rest of the house then cutting in a return will put the basement at a negative pressure, causing it to pull air from outside. The net effect is just a warm basement and decrease in efficiency.

Regarding the outside air intake, this may be required by the local building codes for compliance with IAQ (Indoor Air Quality) regulations. In Texas, I have only seen this applied to commercial or institutional facilities such as office buildings, hospitals, schools, etc. In energy conscious buildings they install CO[sub]2[/sub] sensors which only allow the outside air duct to open when the CO[sub]2[/sub] concentration exceeds 800 ppm or so.
As to whether your house really needs a fresh air duct, building codes notwithstanding, depends on it’s construction. Formerly, it was assumed that homes received enough fresh air by infiltration - leaks along windows and doors and from under the walls. Most homes were/are fairly porous. However, newer homes are generally more tightly sealed in pursuit of greater energy efficiency. In these homes it is necessary to add a controlled amount of fresh air to lower CO[sub]2[/sub] concentrations and to dilute the fumes given off by paint, carpeting, cleaning solvents and armpits :). Chances are, your home is one of these, so I’d advise leaving the fresh air duct in place, or installing a CO[sub]2[/sub] controlled damper ($300 or more.)

If I’m reading question 1 correctly, this hole will be placed after the return opening for the rest of the house. This sounds like you would be introducing unfiltered air into the system – not a good idea, given the sorts of things you find in damp basements.

For your second question…air brought in from outside is necessary in any air conditioning system. Part of the return air is exhausted; the rest is mixed with outside air, and thus becomes recirculated air. Outright removal of the fresh air supply while leaving the return air exhaust in place would mean that you’re removing more air from the conditioned space than you’re putting back in. This results in infiltration – unconditioned air “leaking” into the space. The amount of outdoor air needed depends on many factors, such as the size of the conditioned space and the number of occupants. And, as What Exit? mentioned, outdoor air also serves to prevent problems such as SBS by basically diluting contaminants. This is especially important in newer buildings, which are so heavily insulated (even to the point of having windows that don’t open or are never opened) that the only constant source of fresh air would be that introduced by the conditioning system.

(There are, of course, EPA regulations concerning “clean” and “dirty” outdoor air. I’m guessing that’s not much of a concern for the OP’s situation though.)

(On preview, I see that Rhubarb covered a lot of this. Oh, well…good to know that I’ve gotten something out of those electives. :slight_smile: )

The air isn’t filtered until just before it enters the furnace blower. A hold virtually anywhere in the return system will get filtered before being blown into the house.

Also, are basement floor and walls are poured concrete, so it’s quite dry down there (for a basement) and there’s a dehumidifier running for residual dampness. It pulls out a couple of gallons a day, which is probably less then what the AC pulls out of the rest of the house.

You still need to have some concern with reducing the airflow upstairs too much. Most homes have the minimum airflow for the cubic footage installed by the developer, who is trying to save every penny possible. If you were still on original equipment I would not open a vent in your basement. If you know the system was put in at a higher airflow than rated Cubic footage of the house, you at least will not have this concern.


The real question on the basement return vent is “Where will the air come from to replace what you are taking out of the basement?” If it can be pulled from the rest of the house, it’s not too bad. If it has to be pulled from outside, not too good.

I wouldn’t put a return air grille anywhere that is not also served (even indirectly) by the supply air. I would especially not put any vents in a space that is not sufficiently sealed and insulated. It’s the equivalent of leaving the windows open while the A/C is running. If your basement is well enough constructed, give it a shot. But I think you are just going to end up with a warmer basement and no appreciable savings on your electric bill.

I seriously doubt that there is a dedicated air relief in a residential system. It is more likely that the builder is simply meeting a code requirement with the fresh air duct and that bathroom/kitchen exhausts or just normal leakage allows the extra air to escape the house.