Helpful? 0

Return grilles on wall vs. ceiling

Hello,

My home has return grilles on the wall about 3 ft down from the ceiling on 9 ft walls and about 4 ft down on 14 foot walls on the first floor. In the basement, they are on the wall about a foot up from the floor.

I am planning to install a ERV/HRV to combat elevated humidity in winter; I have had water condense along the ceiling edges and on windows during winter. The ERV/HRV will draw air from the return ducts and dump the fresh air into the basement.

With this setup, I am hoping to somehow draw the moist air in contact with the ceiling into the return grilles on the wall some feet down from the ceiling. If does somehow get drawn, I would appreciate an insight into the physics behind it.

If not, am I then to consider new return grilles on the ceiling? I would like to avoid this to keep costs down.

TIA.

Asked by Venkat Y
Posted Sun, 08/31/2014 - 19:54
Edited Mon, 09/01/2014 - 06:30

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7 Answers

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1.
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Venkat,
First of all, it's unusual for water to condense on a ceiling unless there is a defect in the home's air barrier or a defect in the ceiling insulation. The first step is to try to rectify this problem; a home performance contractor with an infrared camera may be able to help you pin down these defects.

Second: you don't describe the nature of the return air grilles on your wall, but I'm guessing that your home has a forced-air heating and cooling system, and that these grilles are connected to that system.

A forced-air heating and cooling system does a good job of mixing the air in a home when it is in operation, so the location of the return air grilles (wall vs. ceiling) doesn't matter much. If your proposed HRV is properly installed, it will do a good job of lowering the home's indoor humidity level in cold weather when the system is operating, regardless of where the return grilles are located.

Note that this type of system can carry an energy penalty, because furnace blower fans can be energy hogs compared to the fans included in an HRV. That's why ventilation systems with dedicated ventilation ductwork are usually preferred to systems that try to use the ducts designed for a forced-air heating system.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 09/01/2014 - 06:40
Edited Mon, 09/01/2014 - 06:41.

2.
Helpful? 0

I'd do it the other way around, draw exhaust air from various
places around the house [doesn't have to be a lot, just reasonably
isolated from the main ducts to not short-circuit flow paths], and
bring the fresh *into* the return system. That's more typical.

_H*

Answered by Hobbit _
Posted Mon, 09/01/2014 - 07:44

3.
Helpful? 0

Hi Martin,

Thanks for the response. You mention "there is a defect in the home's air barrier or a defect in the ceiling insulation".

1. Can you point me to info on where to look for defects in a home's air barrier? My home is ICF exterior walls with pea gravel underneath the basement slab, and apparently no vapor barrier or insulation underneath the gravel. I also have a wall of average-quality double-pane windows to the north facing a pond. In winter I can feel cold wind coming thru the side sills of the double-hung windows, I recently had a sub-slab depressurization system put in to bring radon levels down from 6.3 to 1.0 pci/l and have begun to run a stand-alone dehumidifier continuously which helps to keep the humidity about 40% RH in the basement.

2. I had a home inspector as well as an insulation pro take a look to the ceiling condensation issue and their infrared cameras showed blue/yellow spots along the edges of the ceiling. There's some discoloration of the ceiling paint tracking the roof joist endings. I currently have R14 fiber glass blown in insulation. The insulation contractor proposes adding cellulose insulation on top. I am in region 5A (east central illinois). What R-value do you think would make the most sense?

3. What cellulose brand is best from an environmental and efficiency stand point?

Thanks,

venkat

Answered by Venkat Y
Posted Mon, 09/01/2014 - 07:52

4.
Helpful? 0

_H*,

Thanks for the suggestion. The reason I am hesitating to dump anything *into* the current duct work is that less-cool humid air in summer could cause condensation in the ducts and in my case could cause mold/rot since the return "ducts" are actually mostly floor joist spaces.

Thanks again,

venkat

Answered by Venkat Y
Posted Mon, 09/01/2014 - 08:05

5.
Helpful? 0

Also, the return grilles are connected to a forced-air HVAC system. I am NOT planning to force-run HVAC while the ERV is running, to avoid the energy penalty of the blower fan. The HVAC and the ERV will just share the same return duct to draw air from.

Answered by Venkat Y
Posted Mon, 09/01/2014 - 08:13

6.
Helpful? 0

Venkat,
As far as I know, building codes require the installation of polyethylene under basement slabs. When was your house built?

R-14 ceiling insulation is a code violation. In your climate zone (Zone 5), the code calls for a minimum of R-38 in ceilings. Make sure that the insulation extends to cover the top plates of your exterior walls.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 09/01/2014 - 08:19

7.
Helpful? 0

Hi Martin,

The house was built in 2002. In trying to mitigate radon, I found a 1 square foot pit in the slab that was left open for the bathtub drain in the basement. That's where I saw that it was pea gravel under the slab. The foreman on the construction crew told me they "probably" didn't use any vapor barrier under the gravel. It didn't occur to me to double check this before I had the pit filled with concrete to try to mitigate radon.

So, I guess I have to have some insulation added to the attic. I read from elsewhere on this forum, cellulose would be best in my situation?

1. Any brands of cellulose you would recommend over others?

2. Also, 2/3 of my home has 14 foot walls and the rest 9 foot. so there's a knee wall that's currently insulated on the sides with batts in between the studs. The studs themselves are exposed. Would it work to have the spray-applied (wet-spray) cellulose applied there?

Thanks.

Answered by Venkat Y
Posted Mon, 09/01/2014 - 08:59

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