Should I block suicide and gable vents in garage?

fastsvo · Jun 18, 2018

I am in the middle of insulating/air sealing and my garage including drywall as well. The attic space will have it's own O'hagin intake vents and a solar fan for exhaust.

Climate = sunny and dry (LA), yet will remain an unconditioned space.
Utilities = Two gas appliances (water heater and HVAC), each have their own vent pipe to the roof.
Purpose = Will remain a garage where I will store cars and use for hobbies.

The home was built in the 60's and has two foundation, aka suicide vents on the bottom and a single gable vent up top (below the new ceiling).

My original plan was to seal these three vents, in order to keep the heat/cold out. Kinda pointless to insulate the garage if I keep these vents open.

I understand that these might no longer be required by LADBS but now the garage is air sealed and "tight", would it still be in my best interest to close these up? Perhaps just leave the gable vent open? What about the fresh air needed for the gas appliances?

Sorry for all the questions, but need to make a fast decision as we are currently in the midst of this renovation.

Thanks!

rsanter · Jun 18, 2018

Are you installing air conditioning?
If not I would leave them and make doors or flaps so you could open and close them when you want.
You will still get some heat gain so if it I still nice outside opening them is an advantage

fastsvo · Jun 18, 2018

rsanter said:
Are you installing air conditioning?
If not I would leave them and make doors or flaps so you could open and close them when you want.
You will still get some heat gain so if it I still nice outside opening them is an advantage

No air conditioning but since I get so much dust coming in from the lower foundation vents (gardner) why not block those and just keep the gable vent open?

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The Tool Tyrant · Jun 18, 2018

You do need 'combustion air' for the water heater and HVAC. The vents that you refer to as "suicide" vents are designed for combustion air.

fastsvo · Jun 18, 2018

The Tool Tyrant said:
You do need 'combustion air' for the water heater and HVAC. The vents that you refer to as "suicide" vents are designed for combustion air.

Ok thanks for clarifying that for me. I am assuming now the single gable vent will not be enough for combustion air?

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fastsvo · Jun 18, 2018

rsanter said:
Are you installing air conditioning?
If not I would leave them and make doors or flaps so you could open and close them when you want.
You will still get some heat gain so if it I still nice outside opening them is an advantage

That's not a bad idea. I'm thinking how about replacing the current foundation vents with something like in the link below so I can somewhat successfully keep the dust and **** from blowing inside the garage?

https://www.lowes.com/pd/Air-Vent-8-in-L-White-Aluminum-Soffit-Vent/3122213

6768rogues · Jun 18, 2018

If your attic is separated from the area with fuel burning appliances, venting the attic will not supply combustion air for the appliances. That is why the vents were there. You could build an enclosure around the appliances and ventilate that enclosure to the outside for combustion air.

dfiler2 · Jun 18, 2018

There are foundation vents that you can close.

https://www.lowes.com/pl/Foundation...pplies/4294512329?searchTerm=foundation+vents

Ole Slewfoot · Jun 18, 2018

Don't you need a vent below the burner of indoor gas water heaters to alleviate explosion risk?

kbs2244 · Jun 18, 2018

I am not familiar with the term O'hagin intake vents
Are the soffit vents?
If so, they with you roof fan should take care of the attic.

If code will allow it (air flow may need to be checked) I would put the louvers over your low vents to keep the dust out.
Just rinse them off when you water the garden.

This will let your space "breathe" with the outside air.

dave_dj1 · Jun 18, 2018

I don't see why you would insulate the ceiling in the attic if the ceiling in the garage is insulated? I've never heard of suicide vents or O'hagan vents either. I had to do a google search for the O'hagan vents.

Vintage Veloce · Jun 18, 2018

The vents at the bottom of the walls are to let heavier than air gasoline fumes out of the garage. If things are properly designed to current building codes, your gas appliances are elevated above the floor well above the height of the floor vents. That way gasoline leaks and the resulting fumes exhaust out the lower vents before getting to the height of the ignition sources in the natural gas appliances.

So... if you have appliances that are ignition sources and keep things in the garage that hold gasoline in the garage, I'd keep the floor level vents.

wssix99 · Jun 18, 2018

The Tool Tyrant said:
You do need 'combustion air' for the water heater and HVAC. The vents that you refer to as "suicide" vents are designed for combustion air.

I'm not so sure about that. (I'm also not familiar with code on these appliances in garages.) Maybe it would be worth checking the code? I know these passive vents are needed for small spaces like closets, but we don't need them for larger utility rooms, etc. Garages should be no different.

The appliances should also be elevated to protect against fume ignition and the fumes should be able to slowly escape around the garage doors, which aren't perfectly sealed.

wssix99 · Jun 18, 2018

Code in my area requires the suicide vents, but I have a heated garage. My City gave me a waiver as I installed a Heat Recovery Ventilator tied to my garage door lights. While those lights are on, the HRV runs and evacuates fumes. (while recovering heat) (There are ASHRAE formulas that can be used to properly size the HRV and run times for this.)

In the summer, I have a problem with heat being trapped in. (Car engines bring in a TON of heat, which can't escape - particularly using the HRV.) So, I replace the heat exchanger/filter in my HRV with a blank insert in the summer so it turns in to a direct vent. (My ceilings get to 120-130 degrees with warm cars inside, so outside is always cooler in the summer.)

fastsvo · Jun 19, 2018

Appreciate all the info!

I have a furnace/AC and a water heater in the garage, neither of them having a dedicated a fresh air tube or intake, but they are mounted on a high box (the return for the HVAC is routed through the cavity of this box).

Sounds like I am keeping these foundation vents. I was suggested to cut down an air filter and stuff it in these vents in order to block the **** from coming in. I think that will cut down the air flow significantly though and raise the risk of things going BOOM.

Vintage Veloce · Jun 19, 2018

I removed the low wall vents from one of my garages, but I took the water heater out of the garage and put in an electric dryer next to the washing machine. The electric drier bothers me a bit still, but I figure that my nose and eyes will tell us if there is a fuel leak before we turn that on anyway.
Note on "suicide vents": Carbon monoxide is slightly lighter than air, and cannot be counted on to leak out of low mounted vents. I think those vents really are for fuel vapors, not CO, so the "suicide" part of the name might be a misnomer.

Stuart in MN · Jun 19, 2018

We don't keep appliances in the garage in Minnesota so I'm not real familiar with the situation, but I suspect the purpose of having vents down low on the wall along with gable vents up high is to provide a 'chimney' effect for air circulation - cool air comes in through the low vents and hot air exhausts out the gables, similar to how a house attic is vented.

fastsvo · Jun 19, 2018

Came across this article that pretty much nullified my original idea:

https://www.garagedoorchildsafety.com/news_time.html

wssix99 · Jun 29, 2018

fastsvo said:
Came across this article that pretty much nullified my original idea:

https://www.garagedoorchildsafety.com/news_time.html

Ventilation is a good thing. If you use a HRV, you can vent without loosing the heat. My HRV is connected to the lights, so it generally runs whenever my garage doors are cycling (carbon monoxide) or I'm in there working.

You'll notice that article also mentions tales of misadventure where people are doing risky things. (hot work on a car, siphoning gasoline in the garage...) Whenever I am doing risky things, such as this, I always crack the garage doors a bit, so I get air exchange with outside. (Garage floors are sloped to the floor so these heavy gasses flow out through the doors.)

fastsvo · Jul 2, 2018

wssix99 said:
Ventilation is a good thing. If you use a HRV, you can vent without loosing the heat. My HRV is connected to the lights, so it generally runs whenever my garage doors are cycling (carbon monoxide) or I'm in there working.

You'll notice that article also mentions tales of misadventure where people are doing risky things. (hot work on a car, siphoning gasoline in the garage...) Whenever I am doing risky things, such as this, I always crack the garage doors a bit, so I get air exchange with outside. (Garage floors are sloped to the floor so these heavy gasses flow out through the doors.)

The question that I cannot find a clear answer on, is how much ventilation do I need? Can I block the lower foundation vents but still keep the gable vent open? From what I have gathered it seems that I still need both style of vents to be functional.

wssix99 · Jul 3, 2018

"2011 ASHRAE Handbook - HVAC Applications (SI); Chapter 15 - Enclosed Vehicular Facilities; Parking Garages" gives the calculations for vent rates required to control the exhaust gasses from cars in garages. For the vent rates to cover the combustion gasses for the appliances, I'd think you'd have to consult their instructions to get the CFM.

Vintage Veloce · Jul 3, 2018

For gasoline fumes, since you have a furnace/AC and a water heater in the garage, I'd DEFINITELY keep the lower vents open.

fastsvo · Jul 3, 2018

Sounds like a plan!

Vintage Veloce said:
For gasoline fumes, since you have a furnace/AC and a water heater in the garage, I'd DEFINITELY keep the lower vents open.

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