Thread: Vent connector

Hi all - I am currently working on my HI licence and am trying to identify the purpose of a vent connector coming out of a return. I was not in the home and have only the pic to go on. Any Ideas? Thanks in advance.


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Originally Posted by Mark M Cooper

Hi all - I am currently working on my HI licence and am trying to identify the purpose of a vent connector coming out of a return. I was not in the home and have only the pic to go on. Make up combustion air (from what I have read this would not be the way to do it)? Any Ideas? Thanks in advance.

You will need to post the photo and a bit more information for anyone to have a clue about what you are describing. Many of the words you use have more than one meaning and even more if you include the misuse of the terms. i.e. a vent connector is a generic term unless you are talking about a gas appliance exhaust flue. A return would commonly mean a return air grill on the conditioned air path in and HVAC system but can have many other meanings.

My original post did not include the edited version of the photo which was suppose to be uploaded. It should now. As I mentioned, I was not in the home so unfortunately I do not have any additional information. I just have not seen a furnace with this type of vent configuration before and was hoping someone could shed some light on what the purpose of this particular vent could be. Thanks

Looks like it is fresh air make up air for a "thigh house" ... too keep it from being "too tight".

Typically, some type of heat transfer device is in that duct to 'pre-warm cool outside air' during winter months and to 'pre-cool hot outside air' during summer months by passing the outside air through a heat exchanger.

Originally Posted by Jerry Peck

Looks like it is fresh air make up air for a "thigh house" ... too keep it from being "too tight".

Typically, some type of heat transfer device is in that duct to 'pre-warm cool outside air' during winter months and to 'pre-cool hot outside air' during summer months by passing the outside air through a heat exchanger.

Thanks for taking time to answer! I appreciate the help.

I can't see it very well in that photo. One thing that threw me off the first time I saw it was a zoned forced air system, with remote dampers. They will often have a bypass back into the system that can look similar to that. It has only come up a few times for me in 15 years. Could be a fresh air intake as well.

Originally Posted by Jim Robinson

I can't see it very well in that photo. One thing that threw me off the first time I saw it was a zoned forced air system, with remote dampers. They will often have a bypass back into the system that can look similar to that. It has only come up a few times for me in 15 years. Could be a fresh air intake as well.

thanks Jim

I presume that you also got the lack of a one foot rise (minimum) where the vent connects to the appliances (furnace and water heater).

Originally Posted by Jerry Peck

I presume that you also got the lack of a one foot rise (minimum) where the vent connects to the appliances (furnace and water heater).

I did. Thanks

Now that the photo is there, my guess is this is a bypass duct that crosses over from the supply side to the return as the other Jim mentioned. As he said it is used in central zoned air systems. The bypass duct allows for excess air pressure to "bleed" to the return side to avoid to much pressure under partial "throttle". This prevents excessive wind noise at theactive registers. Typically there will be a barometeric damper control to prevent loss to the return.