Return Air Vents high or low?
I am working on a reno/addition in CZ 6. The homeowners friend is the Mechanical Contractor on this job. The heating system is an outdoor woodburning forced air with LP back up. He installed the return air vents in the wall cavity ,but they are only 1 inch above the floor. I feel he put in the minimum return air vents. And at the floor? He claims that this method pulls the heat down from the ceiling and warms the room. However in one location there is a heat duct within 5 feet of the return air vent both at the floor. Our walls will have R-31 (2″ EPS with 5.5″ dense pack cellulose) and >R-50 in the ceiling. Is this a good idea for return air vents?
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Replies
Tim,
In cold climates that are heating-dominated, it is usual for both supply registers and return grilles to be located near the floor. For the best mixing, however, return grilles should be located as far as possible from supply registers.
Tim,
I can give you another point of view based on our experiences in NM (CZ4 & CZ5). We found the return to be more effective up high, either in the wall or ceiling. We use IAQ thermostats that move air constantly or very frequently in very tight houses, and doing so, it removes the warmest air up high and circulates it at more even temperature. Its mostly air circulation since the temps in theses houses drop about 1º-2ºF per day w/o heat (we actually did those experiments few years a go in the winter time). In rooms with constant fans, it doesn’t make that much difference.
Is the system up and running? You could measure temperature stratification from floor to ceiling and if it's more than 2 degrees F I'd suggest you'd benefit from a high return.
We build super insulated homes, many with vaulted space and even with high R value roofs we find we benefit from high returns.
Tim,
I think the register location is less important than your curious statement "I feel he put in the minimum return air vents." The return and supply registers and ducts need to be balanced. What did you mean by this?
Unless you're installing AC in the system or using the air-handler for constant circulation, or the house is designed to encourage temperature stratification (vaulted or high ceilings), return grills should be on the floor where they'll pick up the coldest air for reheating, improving the thermal transfer efficiency of the furnace.
This is something I have been wondering about also...in a cold climate where you are heating 6 or 8 months of every year and with higher ceilings it seems a waste to not capture and redistribute the vaulted ceiling heat. If you had a balanced HRV like a LifeBreath with hydronic heating and fresh heated air outlets under the windows and return air inlets on the opposite wall....would it be practical to have an additional system (maybe a cheaper HRV) recirculating the vaulted ceiling spaces and dumping the heated air into the basement. Or would this throw off the balancing of the main HRV? The main HRV would be connected to the outside air and the secondary one only inside.
SquibT,
Then you don't need a secondary HRV, merely a recirculation fan.
What's wasteful is vaulted or high ceilings.
Thanx Robert, as always, you are right about being wasteful but I like the look of a high ceiling with a large stone fireplace chimney as a focal point. Capturing that hot air and hot/warmed air from other points and bringing it down to the basement would be ideal (new construction). I thought a cheaper HRV would give me multiple entry and exit points without having to hire a guy to put in duct work...I could do it. And I would get the added benefit of the cooler air being warmed up a bit. Yes...I understand an HRV is to be connected to the exterior air but can't really see how I can do this cheaply and easily.
Sorry....to clarify this statement...."Yes...I understand an HRV is to be connected to the exterior air but can't really see how I can do this cheaply and easily."....I mean I can't really see how I can do this cheaply and easily....referring to capturing hot air from multiple ceiling locations and distributing the hot ceiling air without wasting it by cooling it thru the HRV (the primary HRV is for ventilation and heating)...and the statement that I know what an HRV does is just to clarify that I do know what they do and how they are used...wish we could edit here....hey! How come EDIT shows up now? and not on my last post?
When a house has strong thermal stratification, with temperatures at the ceiling 10° or 15° warmer than temperatures at the floor, it usually indicates that the house is very leaky. Sealing air leaks goes a long way toward correcting the problem.
An HRV doesn't give "multiple entry and exit points" - the ducting does that. And, since you're not trying to pre-condition outside air but merely move inside air to another location, all you need is a fan. If you want to take air from multiple locations, then you need a multi-port fan which requires ducting to each location.
Check out the Fantech CVS series multi-port units or the Fantech FG series inline fans.
Robert, I menat I feel there could be more returns. i.e. one in each bedroom. I have since discussed this with the contractor. He is going to cut returns into the bedroom after we open up the addition to the existing house. I am not sure why because he already cut in the heat runs, but the atleast he plans on adding them.
SquibT, My electrical contractor installed his return air vents staggered in his great room with a cathedreal ceiling. His Mech. contractor suggested he do this to like you said to redistribute the ceiling heat. And also remove the warmer air during the 2-3 cooling months.
I think we are going to move the one return air to the adjacent wall at floor height and move the other up to the top of the wall. Thanks for the input and suggestions.
Right on Robert....Fantech CVS is exactly what I need...
Thanx for askiing this question Tim...and the added info....
squibt (Tim Shepp)