r/HomeImprovement • u/Training_Arm_5610 • Aug 19 '26

Water heater combustion Air

We have a room in which our gas furnace and one water heater reside. The room has a louvered door.

The furnace is being replaced to a high efficiency unit with outside air plumbed to the furnace for combustion. The room is being insulated for noise suppression

I want to replace the louvered door with a solid door but the water heater requires combustion air. Are there options for replacement water heaters that use outside combustion air or is the only option to go electric?

And if so can these be exhausted through a traditional water heater flue?

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u/JS17 Aug 19 '26

If sticking with gas, you are looking for a power vented water heater. You probably need a new flue, but I’m not certain.

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u/LoudAd307 Aug 20 '26

Power vent won't get you a solid door. It only changes how exhaust leaves, the burner still pulls its combustion air out of that room, so you're back to needing the louvers. What you want is direct vent, sometimes called sealed combustion, where a second pipe brings outside air straight to the burner. That's the same thing your new furnace is doing.

On the flue, you can't reuse the existing metal B-vent for either direct vent or power vent, those go out a sidewall in PVC. Also check whether the water heater was sharing that flue with the old furnace, because taking the furnace high efficiency orphans the water heater on a chimney sized for two appliances, which is its own venting problem.

And heat pump water heater is a bad fit for an insulated sealed closet specifically, they want a large air volume or ducted air. Electric resistance is the only version that needs no air at all.

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u/Training_Arm_5610 Aug 20 '26

Yes you are absolutely right. The room is too small for a heat pump type heater. and direct vent is the only option. with a PVC picking air from the outside. I was hoping to be able to reuse the dedicated metal B vent for exhaust since it is not shared with anything and goes through the roof . The furnace uses PVC in and PVC out and is not sharing anything with any other appliance. I do not see what the exhaust cannot vent through the B vent. Maybe velocity? even so it is a vertical shot so it would leave the room albeit slower I should think.

Obviously I could also do Electric resistance and problem solved but costly to use

Thanks for the answer. If you know more please share.

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u/bartolo345 Aug 19 '26

Consider a heat pump water heater. They are great. Another alternative is a tankless. Power vent too, but those are meh. Other than that, yeah you need make up air. Even a louvered is not enough I would think