Adding More Ventilation with Gas Appliances

[garageuser]

I want to add some ventilation but I'm not sure of the best way as I have two gas appliances in the garage. Right now I leave the doors open when home for a natural breeze but that doesn't work at night or when I'm away. Ideally a solution would be more secure as well.

The back wall has a door to the house, gas furnace and gas water heater. Adjacent corner has side exterior door and two gable vents, one high and one low. The platform the furnace and water heater rests on is a return plenum for the furnace and a bit leaky so occasionally smells from the garage make it into the house.



Currently I crack open the garage door at night with a lock on the tracks but it's not great and it's very tedious to do every night.

One idea was putting a vent fan in front of one or both of the gables but both positive and negative pressured garages seem to have their own issues. Positive pressure could push the odors I'm trying to vent into the house esp with that leaky plenum under the furnace. Negative pressure could prevent the gas appliances from venting naturally out the stack. But maybe the garage is so leaky those concerns don't matter? After all it does have this giant door that's basically a sieve...

Another idea was enclosing the appliances so they have their own separate intake and exhaust. Not sure on feasibility or code requirements but the added benefit would allow me to fully seal the rest of garage to maintain better temperatures in the summer and winter.

There's a bedroom above the back half of the garage with a roof over the front half.

Looking for ideas! Could be DIY or professionally done.

 

[rlitman]

Could you add a fresh air inlet vent to the heater space, and then enclose it with a service door? Then you could have a negative pressure garage.

 

[dcg9381]

You've got an open wall. Why not install an exhaust fan there? Just need to create a little negative pressure.

 

[PoorUB]

Tiny exhaust fan running 24/7.
A 50 CFM bath fan for example. I doubt a 50 CFM exhaust fan would over power the venting for the HVAC and the two fresh air vents. You could put the fan on a timer and run it only at night.

To give you an idea, assuming a 24x24x8 foot garage, a 50 CFM fan will get you one air exchange every 90 minutes.

And yes, you want the garage at a slight negative to the house to keep any fumes from entering the home. Do no put in a fan blowing air into the garage.

If you are concerned about the inside temps and ERV would temper the air that is exchanged.

 

[jkuro]

Start by sealing that return air duct. It's not healthy sucking in car fumes and garage odors, into your house.

Run a 4" dryer duct from outside, into the furnace alcove. That should be enough air for proper combustion.

Call both the furnace and water heater manufacturers and get their take on putting doors on that area.

 

[rlitman]

Start by sealing that return air duct. It's not healthy sucking in car fumes and garage odors, into your house.

Run a 4" dryer duct from outside, into the furnace alcove. That should be enough air for proper combustion.

Call both the furnace and water heater manufacturers and get their take on putting doors on that area.

Yes, sealing the return should be your starting point.

As for combustion air inlet, just reference the installation manual of the appliances. As a rule of thumb though, the open square inches of a combustion air inlet required for a conventionally vented appliance will be the same as the vent area. So, if your appliance has a 5" vent stack, you'll want a 5" hole. I highly doubt 4" will be enough. And isn't that closet on an exterior wall? If so, just put the vent in the wall. I did mine using a pair of back to back 7" wall vent hoods. The exterior one with the flapper replaced by hardware cloth to keep animals out, and the interior flapper left in place. You don't need it mixing air with the outside, just letting make-up air in when venting up the flue.

 

[kaymccampbell]

They sell these nifty fresh air vent things. I've got one wired to my boiler, another wired to the kitchen vent hood, and a third just looking for any relative pressure drop in the house. They all draw air from the attic.

https://www.amazon.com/gp/product/B0083IK7FY/?tag=atomicindus08-20

 

[BillK]

I am not sure what you are trying to accomplish. If the house was built that way it should be fine. You definitely need to seal up the return duct, more for the safety hazard than anything. Unless your garage is totally sealed up airproof I am sure the furnace and water heater will get plenty of air.

 

[jimindm]

How new are the a[appliances? Are they power vented?

New appliances are sort of split. They use outside air for combustion. It ***** from outside and blows back outside. Any kind of negative pressure would be the conditioned air flow. Shouldn't be hard to seal that up from garage vapors.

 

[garageuser]

Thanks for all the info!

I do need to seal up the return air plenum but that's a whole separate topic I'll post in the HVAC section. We don't park in the garage so no car fumes but still not great. I only noticed it when we got the floor resurfaced and some of the poly smell spread into the house. My assumption is through that return and ducts as the door was sealed.

A small exhaust fan is a great idea! I'm thinking up high on the left wall so there's a cross breeze from the vent on the opposite wall. Probably behind where the grey shelves are (far left in photo) as the rest of that wall now has storage shelves.

I really like the low < 100 cfm idea. Enough to cycle the air and hopefully not enough cause issues w/ the gas vents. I'm guessing one of those 300-500-1000 cfm ones is too much?

Sealing off the appliance area would be great but perhaps for the next iteration since that'll be far more work than adding a vent. The back of the closet is against the house and there's a bathroom to the right of it (between water heater and side door) so adding new ducts isn't straightforward, figuratively and literally.