Bathroom Exhaust fans Reduce energy use by 90% and cut through that thick

shower fog

Philip Jones

Problem:

• Failing bathroom exhaust fan – often stalls• Noisy• Built-in light missing its lens• Never happy with performance –

post-shower condensation• Issue of potential mold and

insulation damage• 44W power draw for the trouble

Investigation:

• Fan exhausts into soffit / attic – very bad• Fan 50 cfm; should be at least 70 cfm for room size• Solution should minimize amount of conditioned (heated/cooled) air loss

through exhaust fan while still fulfilling task of clearing humidity (as well as unwanted scents)

• Should support 3 uses of bathroom: teeth brushing, etc.; toilet use; shower use

• Search of replacement fans did not look any nicer, use much less energy or otherwise entice replacement

• Panasonic ERV with heat transfer from exhaust to fresh supply – cool, but cfm too low; application wrong (continuous vs. intermittent use)

• Panasonic ERV search led to best conventional replacement: Panasonic 24.5W

• Even better, Panasonic had Green version: ECM motor at <8W

WhisperGreenLED FV08VKSE3

• 80 cfm / <0.3 sones• 8W or less fan motor• Fan only works as hard as needed by

duct work to meet constant cfm (energy efficiency junkie’s dream)• Two modes – shower vs. settable

simple air exchange – multiple operator control options• Built-in LED 11.5W• “Nightlight” 0.8W (same light dimmed)• Can fully enclose fan with insulation

Ducting

• Aluminum roof vent with damper• Smooth rigid-wall PVC (Al would be

better) ducting with two 45° elbows (better than one 90°) – 7 ft overall run• 3 ft. straight section to first elbow with

slight pitch away from fan (to reduce any condensate back into fan)

• Mastic-sealed joints• Foam board enclosed fiberglass

insulation over fan, initial ducting• Fiberglass insulation over rest of

ducting enclosed by 7” diameter flexible aluminum duct

Shown without insulation in place

Controls:

Requirements• Must support 3 functions in bathroom with minimal air

exhaust to accomplish function• Must automatically turn itself off in all modes (see above)• Must be easy to use and useable without training• Motion sensors work great but what if just brushing teeth?• Moisture sensors work great, but what if just using toilet?

Design• Timer switch to power fan• Toggle switch for low speed (toilet) or high speed (shower)• Upper switch for light; lower switch for nightlight• Lower fan speed setting adjustment under fan grill

Budget

• $395, including ductwork, electric (no labor cost)• $115 (40% ) net-premium for energy saving• Most of the labor is in getting the ducting right• Completely satisfying solution• Using 3 to 8W for fan