Duct configuration

[Gary T. Heller]

The two attached pictures show the termination point of each end of the duct. Many newer homes here have pressure relief registers with attached ducts but this paticular section starts at a distribution box and terminates out through the roof. The distribution box is on the return air side but I have never run across a section of insulated duct terminating through the roof.

[Charley L. Bottger]

Originally Posted by gheller

The two attached pictures show the termination point of each end of the duct. Many newer homes here have pressure relief registers with attached ducts but this paticular section starts at a distribution box and terminates out through the roof. The distribution box is on the return air side but I have never run across a section of insulated duct terminating through the roof.

Well the concept is simple enough just bringing outside air into the return must be a control damper located some where or the unit would have to be very over sized to compensate for ambient temps in AZ of 115+ degrees not my idea of a good system is it a green constructed home

[arook]

Are you sure it was part of the HVAC system? Could it have been an HRV or ERV or bathroom exhaust fan?

[Robert Ernst]

I've seen something like this in Vegas. It was an air exchanger and it was part of the furnace in newer homes. It pulled air out of the ducts and returned air to extra grates in the ceiling.

[Gary T. Heller]

I did look for a damper to see if they were bringing in outside air but there wasn't any.

[Charley L. Bottger]

Originally Posted by gheller

I did look for a damper to see if they were bringing in outside air but there wasn't any.

What did the cap on the roof look like any pics

[Gary T. Heller]

This is a different house but the same style cap.

[Charley L. Bottger]

Does not appear to have room as viewing the pic to have a damper installed If I am seeing correctly that duct to the roof is a 6 inch or am I looking upside down and it is a 9 inch. Either way normally the duct is sized to allow no more than 10% outside air controlled by the size of the duct or a damper preferably the latter. From What I can see in the pic you are drawing outside air whether one wants it or not. I would be asking the installing contractor what their mission to accomplish was as that is only done here on commercial buildings and air tight residential construction

[Gary T. Heller]

I agree Charley...that it was I put in my report.

[Brian A. MacNeish]

Originally Posted by cbottger

Does not appear to have room as viewing the pic to have a damper installed If I am seeing correctly that duct to the roof is a 6 inch or am I looking upside down and it is a 9 inch. Either way normally the duct is sized to allow no more than 10% outside air controlled by the size of the duct or a damper preferably the latter. From What I can see in the pic you are drawing outside air whether one wants it or not. I would be asking the installing contractor what their mission to accomplish was as that is only done here on commercial buildings and air tight residential construction

In Canada, there are mechanical damper/duct systems that bring fresh air into the return plenum. They are controlled by a dehumidistat or programmed timers.