See picture. I have a utility closet in my garage with a tank to tankless hot water heater conversion and a gas heater central A/C. This was like this when I bought the house, except the other night, during record extreme cold, I had to make an emergency temporary cap for a 2" PVC drain pipe in the slab because I realized sewer gases were coming from where a loose 1" PVC drain pipe from the A/C was set in it with an open gap. I was worried if I sealed the 1" pipe to the 2" pipe it would only push the sewer gas problem up into the furnace.

(The picture makes it look like the 1" pipe goes directly into the floor now, but that's just where I set it down. It was previously going in to the pipe under the jar with putting around it. Also there's a washing machine drain in the wall to the left. I went up into the attic to confirm that the washer drain has a vent to the roof, but I don't know if it's upstream or downstream of the drain in the picture.)

I want to put a freestanding plastic garage sink over the drain or roughly in the area where the gray and black footstool is currently. I would then plumb the A/C drain into the sink drain above the sink trap.

picture of a utility closet with tankless water heater and gas furnace and central A/C

Obviously I would fix the mess with the gas lines, routing them closer to the wall and using less flex line. I'd do something to ensure access to the tankless heater, either by building a framework for a kneeling board you could lay across it or make the sink removable with quick disconnects.

Some questions about this (aside from, can a sink safely go here at all) are: can I reduce the size of the utility closet turning the sink area into an alcove? Alternatively can/should I leave the whole area open to the garage? Or keep the sink behind the existing utility doors over this area.

A consideration is I use a mini split to heat/cool the garage, but the utility closet has a large vent hole to the attic (visible in the 1 o'clock sector of the picture). I spend a lot of time in the garage working on projects, so I also want to limit my exposure to combustion products from the two gas burning appliances here.

  • The thing that gets my attention here is the rising damp.
    – Jasen
    Dec 25, 2022 at 12:58
  • 1
    Kudos to you for separating these questions from the plumbing ones. I think you organized project nicely into two questions. I hope you'll post an answer with a photo when you're finished.
    – jay613
    Dec 25, 2022 at 14:14

2 Answers 2


Your furnace will have instructions on required space on all sides. In the manual or on a sticker somewhere. You can probably move the left closet wall to so it sits on the left edge of the pedestal, and your water heater and new sink will be outside the closet. You could eliminate the closet entirely but I think it's useful to keep dust and dirt off the furnace. You could put the sink in the closet but I think it will be nicer and more convenient if you move the wall as suggested.

It looks like the furnace burns room air, so the closet door needs vents that are large enough per the furnace's instructions.

The closet cannot and should not separate you (in the garage) from combustion products. Those should be going up the flue! You can, should, must install a CO detector in the garage to make sure of that. If the closet door doesn't have a sufficiently large vent, then there will be combustion products inside the closet and you'll have lots of other problems. I think the main purpose of the closet is to keep the furnace clean, especially if you're doing woodwork in the garage.

If there's a door from the garage into your house you should put another CO detector just inside that door too.


I spend a lot of time in the garage working on projects, so I also want to limit my exposure to combustion products from the two gas burning appliances here.

A closet won't help with that much, so long as the flues and make-up air vents are working you're golden. Make sure you have a working carbon monoxide alarm.

can a sink safely go here at all.

There are rules for spacing between sinks and electrical appliances.

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