System Pros and Cons

Exhaust-Only Whole-Building Ventilation
Pros Cons

Single-point systems offer the least expensive first-cost approach to adding whole-building ventilation


Often an upgraded bath fan, so most familiar equipment for contractors and electricians to install. Makes installation and operation simpler


Generally the least costly system to operate at 5 - 60 watts


Depressurizes living space: in temperate to cold climates, cool outdoor pulled into wall cavities avoids condensation problems in walls


Exhaust fans are familiar to occupants and have low maintenance requirements

Source of incoming air is dispersed and unpredictable, so cannot be filtered or dehumidified. Fresh air inlets are only effective if the house is very tight


Incoming air is not tempered, so ventilation may be perceived as draft, especially in very cold climates


Outdoor pollutants (including radon, if present) may be drawn into home


Depressurizes living space: in hot, humid climates, moist outdoor air pulled into wall cavities can condense against cooled interior wall when AC is operating, causing moisture problems and mold growth


Depressurization may cause backdrafting of naturally vented combustion appliances


No distribution system


No option for filtering incoming air

Existing Air Handler Whole-Building Ventilation
Pros Cons

Uses existing furnace, heat pump, or AC air handler plus existing ductwork, which limits first costs


Air handler is familiar to contractors, so installation procedures are familiar


Provides opportunity to filter and/or temper incoming air


Outdoor pollutants (including radon) are not drawn into the living space because dwelling is pressurized

Increases electrical use, since air handler operates for ventilation when no heating or cooling is needed


Air handler wattage is usually 300-500 watts. Use of ECM or BPM retrofit motor can reduce energy use by up to 80%, but adds to system cost


System relies on negative pressure on return side to pull in required amount of outdoor air, which is difficult to control. Difficult to verify air flows. Multi-speed air-handlers complicate this problem, since outdoor air intake varies with the fan speed.


In very cold climates, pressurization can drive indoor moisture into walls, increasing risks for mold and rot


Requires applying ASHRAE 62.2's Effective Ventilation Rate formula for intermittent ventilation


Still need bath and kitchen fans for local exhaust ventilation


Requires correct programming of controls and training of homeowner for proper operation and maintenance


Some air-handler manufacturers limit return-air temperatures to avoid equipment damage

Dedicated Supply Fan Whole-Building Ventilation
Pros Cons

Supply fan filters incoming air


Electrical use comparable to exhaust-only system: 10 - 90 watts


Known source of supply air; system designer can avoid bad locations for outdoor air intake


Outdoor pollutants (including radon) are not drawn into the living space because dwelling is pressurized

No tempering of incoming air


Extra fan or fans, so increased equipment & installation cost


Route of exhaust air is unknown


In very cold climates, pressurization can drive moisture into walls


Still need bath and kitchen fans for local exhaust ventilation

Balanced System with No Heat Recovery Whole-Building Ventilation
Pros Cons

Incoming air can be filtered


Known source of supply air; system designer can avoid bad locations for outdoor air intake.


Minimizes pressurization or depressurization with balanced flow.


Simple system may have one exhaust fan matched to one supply fan


Can use bathroom pickups instead of bath fans for local exhaust ventilation


Installation cost lower than ERV or HRV

Difficult to temper unless blended with household air


Use limited to warm, temperate, and cool climates; not a good choice for very cold or hot/humid climates


Difficult to distribute unless system uses dedicated supply ducts or is tied to air handler


Unfamiliar system for contractors to install


Unfamiliar system for occupants to operate and maintain


Installation cost higher than exhaust-only or supply-only systems

HRV or ERV Whole-Building Ventilation
Pros Cons

Incoming air can be tempered and filtered


Known source of supply air; system designer can avoid bad locations for outdoor air intake.


If ducted or tied to air handler, ventilation air is well distributed and mixed


Best system for very cold climates (HRV or ERV)


Best system for hot, humid climates (ERV)


Recovers heat and/or moisture from outgoing exhaust air


Minimizes pressurization or depressurization with balanced flow


Can use bathroom pickups instead of bath fans for local exhaust ventilation

Can be high energy user. If tied to air handler, may use 25-350 watts for heat exchanger, plus 300-500 watts for furnace or heat pump air handler continuously


Generally most costly approach


Most complicated design and installation for contractors


Air flows must be measured and balanced


Needs most maintenance: filters need changing or cleaning which requires both access and homeowner awareness


Most effective in very tight homes with extreme climates and/or high energy costs


Unfamiliar system for occupants to operate and maintain