Energy Recovery Ventilator vs Exhaust Fan

[Joe Reilly]

Our course this week I had the privilege of inspecting a new build.

It had 3 bathrooms, 2 of which had exhaust fans, however the 3rd had what looked like at time a return air supply duct without a filter.

Well, I called it out for not appropriate ventialtion in the bathroom and the builder came back sayings it has a ERV system connected. (Odd 1 of 3 had this), Anyway there was not an on/off feature for this ERV system, and attic acess was blocked off so I could not check the unit.

My question is, are ERV's suitable and are the considered a replacement for the mechanically vented requirement ?

Builder reply "There is a fresh air fan installed in your attic servicing this hallway bathroom and the laundry room"


Any information on this matter would be appreciated.

[Jerry Peck]

Hopefully Gunnar will reply with California specific requirements. Until then, this is from the IRC:

TABLE M1505.4.4
MINIMUM REQUIRED LOCAL EXHAUST RATES FOR ONE- AND TWO-FAMILY DWELLINGS
AREA TO BEEXHAUSTED EXHAUST RATES
Kitchens 100 cfm intermittent or 25 cfm continuous
Bathrooms-Toilet Rooms Mechanical exhaust capacity of 50 cfm intermittent or 20 cfm continuous

An ERV could ... could ... work as long as it meets the minimum required ventilation of 50 cfm minimum for on/off exhaust fans or 20 cfm for continuous (no off switch) exhaust fans.

Designing an energy recovery component to a bathroom exhaust fans seems as though it would only work with a continuous fan.

[Joe Reilly]

Hopefully Gunnar will reply with California specific requirements. Until then, this is from the IRC:

TABLE M1505.4.4
MINIMUM REQUIRED LOCAL EXHAUST RATES FOR ONE- AND TWO-FAMILY DWELLINGS
AREA TO BEEXHAUSTED EXHAUST RATES
Kitchens 100 cfm intermittent or 25 cfm continuous
Bathrooms-Toilet Rooms Mechanical exhaust capacity of 50 cfm intermittent or 20 cfm continuous

An ERV could ... could ... work as long as it meets the minimum required ventilation of 50 cfm minimum for on/off exhaust fans or 20 cfm for continuous (no off switch) exhaust fans.

Designing an energy recovery component to a bathroom exhaust fans seems as though it would only work with a continuous fan.


Thank you Jerry, I was not sure if ERVs came into the classification of exhaust fans.

[Jerry Peck]

I was not sure if ERVs came into the classification of exhaust fans.

That would depend on the design of the ERV.

ERVs are basically a pipe from inside air to outside air with a chamber around it to allow transfer of heat between the two to allow heat generated for the inside to be transferred to the cold air coming in from the outside, or cooled air generated for the inside to be transferred to the hot air coming in from the outside ... very basically speaking.

If the 'pipe' is connected to a bathroom exhaust fan, for it to work with efficiency, the exhaust fan would need to be on continuously, or switched on from two locations: the bathroom when that is in use; and/or the heating/cooling system when ithat is in use. If the fan was already on for one use, and the other use then called for the fan to be on, neither "on" switch would shut the fan "off". Both fan switches would need to "off: for the fan to turn "off".

Noncontinuous operation requires 50 cfm minimum when on. Continuous operation only requires 20 cfm and to be continuously on.

Seems to me like they may be trying to eliminate one penetration through the thermal envelope, which makes sense, if done correctly.

[Markus Keller]

Just saw one of these set ups in a Condo unit yesterday. Seen them many times in newer houses but this set up was a new one.
S & P TR130 total recovery unit, only served all 3 bathrooms. 4" intake at each bathroom with a switch, big unit in master bedroom closet.
Maybe on paper it all makes sense. Seems stupid though from a job site perspective. Don't know how it would save money or be sufficiently better to justify use.
My guess is its working on some theory of lowering the furnace BTU since you don't just have exhaust fans sucking all the air out.
Still seems dumb for a Condo.

[david shapiro]

If the 'pipe' is connected to a bathroom exhaust fan, for it to work with efficiency, the exhaust fan would need to be on continuously, or switched on from two locations: the bathroom when that is in use; and/or the heating/cooling system when ithat is in use. If the fan was already on for one use, and the other use then called for the fan to be on, neither "on" switch would shut the fan "off". Both fan switches would need to "off: for the fan to turn "off".

((Parenthetically)), such a fan would need to be fed by the air handler circuit. If a listed air handler specifies that it must have its own circuit, doing so would require Special Permission. Perhaps it could be managed by supplying the fan from the bathroom circuit, and also using it to power a relay that sensed when the HVAC went on. But then is the local shutoff truly a shutoff? I've seen weirder, more-complicated designs.

[Jerry Peck]

... using it to power a relay that sensed when the HVAC went on. But then is the local shutoff truly a shutoff?

It could be controlled by a relay, which would be easier, in that case, or by 3-way switches or 3-way and 4-way switches which could be used when one larger exhaust fan is used for exhaust from more than one bathroom (as frequently done in more expensive homes to remove the fan noise source from the bathroom to either in the attic or roof mounted).

Using a relay in that case adds another component to fail and needing to be accessible for repair, versus using 3-way and 4-way switches.

[david shapiro]

This makes sense, Jerry. If there is one large remote fan motor, sure, use relays or what-all.
My main concern is with clean circuiting. If there are local fans, here and there and there, and their controls all interact with the air handler, I want one CB marked as serving all of this.

Even beyond this, I want a local disconnect, an absolute, no-override disconnect, for every local fan. That's Part III, Disconnecting Means, of NEC Art 422, Appliances. Okay, unless the circuit breaker is equipped with a padlock jobbie. It doesn't have to be the regular wall switch, but it has to be in the room.