Attic Furnace

As home space became increasingly scarce and fewer homes were built with basements, architects and home builders turned to putting the furnace and HVAC air handling unit in the attic. While this is a seemingly good answer to the problem of where to put the unit, it has pros and cons. The current design is moving away from this option, as the tides of thought focus more on the cons of such an installation than the pros.

Before installing an attic furnace in a new home, it’s a good idea to weigh the pros and cons, looking for what will work best for the home. While the trend is moving away from attic furnace installations, that doesn’t mean there aren’t cases when it still makes sense.

Attic furnaces and HVAC units differ from those intended for basement use. They are designed to be mounted horizontally rather than vertically. This is especially important for gas-fired furnaces, as the gas burner must be mounted correctly. A basement unit installed horizontally in the attic may not work at all or may be more susceptible to causing a fire.

Of course, if a furnace is installed in the home, replacing it with something similar makes more sense. Switching from a basement furnace installation to an attic one or from an attic to a basement is considerably more expensive due to installing all new ductwork throughout the home.

Benefits of an Attic Installation

The most obvious reason to install the furnace in the attic is to save space. Most people don’t effectively utilize the space in their attics anyway, so putting the stove up and the necessary ductwork doesn’t take up otherwise usable space. However, installing a furnace in the attic is usually cheaper, especially when new construction is done, because a shorter chimney can be used. Installing ductwork in the attic can be easier than installing it in the basement.

There isn’t a home design where an attic-mounted furnace won’t work unless there is no attic. The downflow air design of an attic furnace works in all homes. There are many installation options in the attic, where gas and electric furnaces are possible.

Disadvantages of an Attic Installation

However, everything is not perfect in the world of attic installation. The biggest drawback to installing an attic furnace is that it tends to provide lower efficiency. This isn’t the fault of the furnace design but rather simple physics. However, using a high-efficiency furnace can overcome some of this.

Everyone learns that heat rises and cold drops. This is part of how a home furnace in the basement works. Warm air from the furnace is pumped through ductwork to the upstairs, under pressure, where it warms the home. As it does, the air loses its heat and gradually returns to the basement, where it can be warmed again.

With an attic-mounted furnace, the air being brought into the furnace intake comes from the home’s upper story or the ceiling of a one-story home. Either way, it’s the warmest air in the house, being reheated and then circulated back into the living areas. It is not uncommon for the floor level of a home to be a few degrees higher than the ceiling level.

This same problem that makes an attic-mounted furnace less efficient will make an attic-mounted air conditioner more efficient, as the air brought into the HVAC unit will be the warmest in the home’s living quarters.

Attic installations can also cause maintenance problems. Because the unit is away from the family’s activities, any problems with it can go undetected until they are causing a problem. While these are usually minor problems, they are a nuisance nonetheless.

Is an Attic Installation Safe?

Attic installations of both gas and electric furnaces are perfectly safe when professionally installed. This is not the sort of project a homeowner should take on themselves. If the unit has a combination heating and air conditioning system, the homeowner cannot legally remove the Freon from the old unit and install it in the new one. Special equipment, training, and certification are required for this.

Maintaining minimal space around the furnace is necessary so that flammable materials other than the home’s framing cannot be introduced. This is no different than for a stove installed in a basement, but it is easier to make a mistake in the attic, especially with insulation.

The attic should be insulated before a furnace is installed in an attic. It is usual for insulation to go under the HVAC air handling unit, but it is almost impossible to put it there once the unit is in place. The same goes for the ductwork, to a lesser extent, as the ducts are generally of a smaller dimension than the HVAC unit itself. Insulating beneath these will help hold the heating and cooling in the living portion of the home.

But insulation shouldn’t stop there since the bulk of the attic space is not usually insulated. The ducts themselves need to be insulated so that the air passing through them is not heated or cooled by the ambient air in the attic. The most common materials are insulated ducts of a similar bubble pack or fibrous fiberglass matt. Even then, it is a good idea to add another layer of thicker insulating blanket around the ducts, as the insulating value of the ducts themselves isn’t all that high.

The HVAC unit should be avoided when installing blown-in insulation in an attic, especially access panels and air intake grilles. While building blown-in insulation around the ductwork is fine, the air handling unit must be given free maintenance access to prevent fire risk.

Installing a Gas Furnace in the Attic

Gas furnaces in the attic require a gas line to be brought up from the home’s ground floor and a furnace flue or chimney installed. The plumber will typically install the gas line for the home’s construction. The furnace should be pressurized and checked for leaks using soapy water before being connected to the gas and turned on.

A double-wall chimney pipe is required to meet the building code. This provides an air space between the active part of the flue, where the hot exhaust gases are passing, and the outer skin of the chimney. The space between the two walls is left open at both ends, allowing air to pass through by natural convection. This helps prevent the danger of any heat buildup. If the chimney pipe is enclosed in any way, a minimum of two inches of space is required between the outer wall of the pipe and the enclosure.