Less isn t good especially in winter when drafts tend to run higher.
Furnace closet door requirements.
All penetrations must be air sealed as well.
A furnace malfunction can cause a deadly carbon monoxide co buildup.
Replace the door by reattaching the hinges.
Enclose any furnace cabinet with gypsum drywall which is fire resistant.
The door must have weatherstripping and a threshold to prevent air leakage between the closet and the house.
Door assembly shall meet the requirements of section 504 1 1.
The door assembly shall be installed with a threshold and bottom door seal and shall meet the requirements of section 504 1 2.
Be sure to caulk around the seams to make a tight seal.
In this arrangement the general rule is that your furnace room cannot be smaller than 50 cubic feet per 1000 btus of heat the furnace produces.
Cut off the bottom few inches of the door with a circular saw to create a gap that allows air to vent into the furnace room.
This almost certainly means that you will need to add a basic vent to your closet so that it can bring in a flow of new air for combustion.
Combustion air for such installations shall be obtained from the outdoors in accordance with section 506 4.
Once your combustion vents have been installed and the ceiling in the closet has been finished out you will want to close off any vents in the door.
Place the door across two sawhorses.
More well judgment call but be sure the draft isn t so strong it is creating an air curtain across the discharge into the draft hood more likely on the water heater in my experience.
The key is that you have to install air inlets so that the furnace or water heater gets the combustion air it needs when it s running.
Refer to the furnace installation.
When locating the walls be sure to allow enough space at least 30 inches to move around inside the furnace room so that maintenance and repairs can be performed on the furnace.
Unscrew the hinges from the furnace room door with a screwdriver.
The closet shall be for the exclusive use of the water heater.
Provide a door with a vented front large enough to provide the necessary air supply.
Keep checking the draft also for good measure open and close the garage door and an outside door on another side of the house note you want the draft to be between 0 01 and 0 02 water column inches.