Space is one of the most important considerations when installing a new furnace. Many units are installed in garages or attics, where there is enough room to fit the unit in a corner. But if all you have are crawlspaces, then you may be wondering what corner will work for a new furnace system. Manufacturers understand this problem, and in many cases you can install the furnace in a utility closet, as long as you have enough room.
Ventilating a closet is generally easy to do. Furnaces have their own supply and exhaust vents that need to be installed along with the unit. Depending on building codes in your area, you will need to install either a double pipe system or a single pipe with a double inner layer. The size of the exhaust vents will depend entirely on the size of your furnace; the size of the closet does not matter. For safety, you need the required venting, but as long as you extend pipes to the roof or outside walls, you do not need to worry about the closet. Space and heating issues are much more important concerns in closet installation.
When installing the system in your closet, make sure your door is large enough for the widest part of the furnace. If you have other appliances in the utility closet, make sure you can remove them without disturbing the furnace once it is installed. You will need to do maintenance and repairs in the future, so having access to control panels is also important.
The heat that the furnace radiates may lead to a fire hazard. This is where ventilation become important -- not the ventilation of the furnace itself, but the ventilation of the closet space. The heat can safely escape if there is space around the furnace. Do not install your furnace in a storage closet. Any type of flammable material, including insulation, needs to be removed before installing the furnace.
Venting Without Pipes
If you decide to install your furnace without piping to reach outside air, then venting may be a concern. 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. 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.