Return air from the outside

[Kevin Fuaua]

Hey all.

I did an inspection today on a 5 year old condo that had a Trane Heat Pump.
This system had an additional air return that ran from a roof vent to the return chase. This by passed the filter and draws in additional air from the outside.
Anyone ever see, know, explain what's up?

Kevin

[Markus Keller]

In commercial work thats typically called makeup air and is required depending on specific occupancy.
It is atypical for residential but I have seen it. Installation unfortunately sounds wrong from what you are describing.
You may want to think about interior conditions, interior return set-up and air quality issues to figure out any clues as to why it was installed. Other than that write it up for removal or compliant installation.

[Darrel Hood]

Make up air should be routed through the filter or have a dedicated in line filter.

[Scott Patterson]

Make up air should be routed through the filter or have a dedicated in line filter.

As Darrel said, it ain't right!

[Jerry Peck]

Make up air should be routed through the filter or have a dedicated in line filter.

"should" as in 'not required to be, but for best practices, filtering the incoming outdoor fresh the outdoor air helps catch particulates and other items depending on the quality of the filter'.

[Dan Cullen]

It's a poor man's method of improving diluting indoor air contaminants w/o spending money on an ERV or HRV. It can be an okay solution if it's combined with intake damper controls, a fan cycler, filtration, etc. I've got a nice diagram and article on it on my other computer. I'll send it along later.

[Vern Heiler]

Most, if not all, of the manufactured (mobile) homes have the make up air as a duct through the roof and into the return air plenum, which is a closet. The air filters are gently placed on top of the open A' coil where the air flows freely past the edges.:)

[John Kogel]

I recently found a gas furnace and return air duct in a crawlspace with two return air inlets open to the crawlspace. The crawlspace was clean with a concrete floor, but I still brought it to my client's attention.

In fact, I suggested they might want to cap those two inlets, but that I couldn't say whether it was detrimental or not. It is one of those things that may work well in one house and be a problem in another, IMO.

[Rod Butler]

An outdoor air intake is desirable on most any system. However it must be ran thru filters as some have mentioned above and the filters need to be upstream of any coil or heat exchanger. A damper is also desirable.

The outside air volume taken in will be limited to the amount of ex-filtration if left undampered, but this can be very expensive, especially if you have a leaky older home or you have kids. Because kids don't always know how to shut the door.

I can still here my dad; "shut the door I'm not going to pay to heat the entire neighborhood!"

:D

The benefits besides reduced infiltration are potentially cleaner air and a cleaner home because the space is under a positive pressure.