Is Moving the Furnace to the Attic Better Than In a Closet

Some of the differences are notable:

Noise
Comfort
Drainage
Flooding
Safety
Serviceability

The Furnace Located in the Closet Versus the Furnace Located in the Attic

Noise: Moving your forced air heater and evaporator coil to the attic normally results in a lower noise level. I say “normally” because the noise is lowered only if the return air ducting is installed correctly and is the correct size. Most attic installations significantly reduce the amount of wind noise from around the blower motor by placing the motor father from the entrance to the home. Most homes here in Southern California are built on a slab. When the noise from the fan motor is generated it bounces off the concrete and into the home. This is even worse if the area in front of the closet furnace is floored with tile, granite or marble. The humming or transformers is reduced in a quality attic installation and rarely can be heard at all. Vibrations are reduced in the attic through the use of dampening pads or hanging the furnace and coil from the rafters. The attic location for the furnace is better for noise reduction.

Comfort: In the cooling season the attic location with the ceiling level return air register(s) is better for cooling air distribution. The hottest air of the home is cooled down and a pattern of circulation is made. This pattern of circulation helps to ensure that no stratification of heat is in the home. Hot spots and cool spots even out making the home more comfortable to live in. In the heating season the close furnace with a return air register at the lowest part of the home is better for the same reasons that the ceiling level register is better in the cooling season. Both closet and attic furnace installation can be fitted with additional return air registers to solve the stratification problem.
Drainage: today’s 90% AFUE furnaces and all evaporator coils need a drain. It is easier to drain an attic furnace installation than a closet furnace installation if the closet furnace was not built with air conditioning in mind with the home. Condensation pumps installed in closets work just fine for draining condensation from the evaporator coil, but not so well when draining the acidic water from the 90% AFUE furnace vents. The acid reduces the lifespan of the condensation pumps and they wear out quickly.

Flooding: Condensation lines can plug up and flood your home. We see this all the time. An up flow furnace installation in a closet can be protected very well through the use of a float switch, but if the pump fails or the evaporator coil pan rusts out or cracks the home can still be flooded. An tic installation is less prone to flooding as the pan in the evaporator coil has 2 drains, not just one drain like an up flow furnace, as well as a float switch to shut the furnace off in the event of a stoppage. The evaporator coil and the furnace (90% AFUE only) are completely set in water proof pan(s) and these pans are wired to shut the furnace off in the event of water buildup. Logically just about everyone thinks that the attic furnace is more prone to flooding, but that is not the case. The attic installation is safer from a flood perspective.
Safety: Attic installations and furnace installations do not have significant safety differences. Both of these installations are safe when installed properly.

Serviceability: Hands down the furnace installation is easier to service, but this ease of service leads to negligent service. The number loss of heating and cooling in your heating and air conditioning system is through the ducting. Poor and loose connections and a lack of insulation material on the joints in a home ducting system leads to an average of more than a Ton of air conditioning loss in the cooling season and nearly that much in the heating season. Most heating and air conditioning technician service a furnace and never even look at the ducting. There are even a number of HVAC companies and 2 leading national organizations that preach avoiding the ducting. According to these companies and these national organizations the profitability in repairing ducting is low and therefore should be avoided. We repair ducting every day because it leads to a more comfortable and cleaner indoor air environment, not because of profitability.