Residential Evaporator Coils Placement

[grahamW]

A quick question regarding the placement of the evaporator coils placement on top of a residential furnace. Within the plenum above the furnace, is there supposed to be a gap between the coil and the top of the furnace? If so, how much of a gap and what supports the condensate tray. Mine currently rests directly on the top of the furnace whereas my previous home had it located further up the plenum.

Thanks.

[Big Chicken]

I think this depends on the brand you have and how it was installed. I've seen some ingenious installations before in a plenum that involved custom work. I've also seen some scary setups that resulted in condensate running back into the furnace instead of out the condensate hose. Some brands use a coil box that screws right to the furnace itself, leaving very little gap between the coil and the furnace. Condensate trays can vary as well based on the shape of the coil.

[jimbo]

Unless your coil is matched to the furnace...unlikely that a new coil will be a match to the old furnace....then some creative sheet metal will be required. No problem.

[jadnashua]

One thing often specified, and probably as often omitted, is a decoupling section of plenum or ductwork between the working hardware and the rest of the ductwork. This is often a short plastic coated canvas section. It is quite important to prevent vibrational noises from the HVAC plant into the rest of the ductwork. Drain pans sometimes have a redundent, overflow pan - you really don't want that condensate draining through your furnace! On my air handler, it's designed as an upflow, and it's below the working parts, but most furnaces are designed with it after, or above.