Why Is The Air So Hot When It Comes Out Of The Ductwork In Your Home?

If you have experienced warm air blowing from the supply ductwork in your home during the summer time, it’s a normal and unfortunate occurrence in Phoenix homes.  Normal, because our ductwork and air handlers tend to be in the attic, which is above 140 degrees in the summer in Arizona. Unfortunately, because a Phoenix attic is the last place our ductwork and air handlers should be located. Our cooling dominated climate demands the most from our AC units in the summer and because all of its components are in the attic, it has to work even harder to keep us comfortable. That is why it’s important as homeowners to do everything we can to make sure our units operate as smoothly as possible with sealed ductwork, balanced airflow, proper insulation and shade along sun struck windows.

In an Arizona summer, that super heated air easily transfers from the attic into the ductwork, and the house if the attic is not properly insulated. [Note, I said properly, not well insulated]  While the air conditioner is off, hot attic air is transferring into the ducts and waiting… waiting for the air to kick on so it can get flushed out into the home and rooms. There are some things you can do to help slow down the transfer of that heat to minimize that hot, uncomfortable air the first 30 seconds of the air conditioning turning on. Below is a list from most effective to least effective ignoring costs.

1.       Spray foam the attic roof slope to make your attic conditioned space.

2.       Bring the attic into conditioned space.  This can be done by netting and blowing insulation along the roof slope or completely enclosing the ductwork in a foam board box.

3.       Cover the ductwork in insulation.

4.       If you have the opportunity, change the ductwork to R-8 insulated flex duct.

5.       Add passive ventilation like a ridge vent (no attic fans of any kind) if you live in a ranch style home with no side ventilation (bird hole vents).

Now here is the same list taking into account cost, practicability and effectiveness, in other words what most homeowners should do.

1.       Cover the ductwork in insulation.

2.       If you have the opportunity, change the ductwork to R-8 insulated flex duct.

3.       Bring the attic into conditioned space.  This can be done by netting and blowing insulation along the roof slope or completely enclosing the ductwork in a foam board box.

4.       Spray foam the attic roof slope to make your attic conditioned space.

5.       Add passive ventilation like a ridge vent (no attic fans of any kind) if you live in a ranch style home with no side ventilation (bird hole vents).

By insulating the ductwork, plenums, and duct connections, we are slowing the transfer of heat into the ductwork.  Bringing the attic into conditioned space dramatically cuts the attic temperatures and I love this solution, but it comes at a significant cost, about 5-6 times more than just insulating the attic. Spray foam is a great solution for new construction, but not cost effective more existing homes. If your home was built during the 70’s with gray ductwork, chances are it is splitting and starting to crumble due to poor product quality. This is a good opportunity to upgrade to an R-8 insulated duct.  Netting and blowing insulation along the roof truss is another good option but may not be feasible because of space restrictions in the attic. Passive ventilation in ranch style homes with no bird vents will help cool the attic a few degrees.