On air leakage, insulation & r-values

Concerned about R-Value’s in your new whole house fan?
Here’s some engineering facts you should know.

If you live in a four-season climate, it’s important to prevent warm, moist indoor air from entering a cold, dry attic in winter. Air leakage like this can create condensation in your attic, which can result in costly water damage over time.

One of the key design criteria for AirScape whole house fans is to prevent this from happening. All our units use automated, insulated steel doors, controlled by a premium industrial actuator to ensure a positive seal, over and over again, for many years.

One of our competitors — who also uses an automatic door design — makes a big deal about the R-value of their doors, as if this was the critical design factor in whole house fans.

Insulating the doors is important — it prevents condensation inside the fan. But the critical factor in avoiding attic damage is not insulation, but preventing air leakage. Obviously, R-22 makes no difference if your doors leak air. That’s why our innovative AirScape 1.7 uses all-metal construction, steel doors and premium industrial actuators: to create a strong mechanical framework that ensures a tight, reliable seal, every time, for many years. It’s one of our key selling points. Our 3.0 goes even further, with a heavy industrial-grade aluminum damper system that can hold a tight seal in near-hurricane force winds!

With that in mind, let’s talk about insulation. The doors on the AirScape 1.7 use two inches of fiberglass insulation, which delivers about R-7. This may not sound like much, but it’s enough — even with a 90 degree temperature difference — to prevent condensation inside the unit.

Now, we could use two inches of PolyIsoCyanurate (PolyISO), instead of fiberglass, like our competitor. By our calculation, that would deliver about R-15. (We’re not sure how they get R-22 out of their two inches of PolyISO, but we feel they should share their secret with the rest of the building industry!). We chose fiberglass because it is a better sound attenuator (it helps make our fan quieter), and the difference between R-7 and R-15 for this application is trivial.

Here’s how trivial: all other things being equal (like no air leakage!) the difference in conductive heat loss between R-7 and R-22 would cost less than $1.00 per year.

Of course, if you have a special application that requires extraordinary insulation, or just sleep better at night knowing you’re all R’d up, our AirScape 1.0 fan uses a more traditional design and three inches of PolyISO, for true R-22 insulation.

Still have questions? Call or email us.