Open duct over HRV fresh air supply to furnace

noticed an opening in a T junction of a duct above a fresh air feed from the HRV to the furnace ducting. (Pulsed-air electric furnace)
My first thoughts are that the pull /neg pressure from the furnace fan will not affect the HRV’s function. I am missing something? Should this be capped or left open?

This is located in a mechanical room/closet in in the basement of a row townhouse.

If I am understanding your picture/description correctly, that should be capped. Otherwise the furnace will be pulling room air in with the fresh air from the HRV (unless that is what the HVAC tech who balanced the system intended).

BTW, use of that T there screams DIY. Be on the lookout!


Hi Laurent! I’ve seen this before and you’re probably right about the reason for it…What is the HRV make and model?

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Hey Ryan, Thanks for the reply. I am thinking that that may be what the tech intended because there is no other return in the basement. I modified your diagram to better explain the set-up…
hrv diagram


Hey Marcel, long time no chat.
The HRV is a Fantech VHR 1404 B

That is definitely possible. Sloppy way of doing it if you ask me, but whatever works, as long as the system is balanced! Was there a balance tag/sticker on the HRV? If not, you could recommend that the client have the balancing checked/verified.


This is the only sticker from a tech…pretty vague.

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Attached pictures are from Fantech VHR manual at link:

You can see the open connection at the return air and explanation.


Thanks Marcel. That lays it to rest definitively. Have a great evening!

I don’t see what you guys are seeing in that diagram. The graphic is not representing an open connection at the return air. It is simply a cut off version of the graphic I posted above. The “stub” labeled Return Air is representing the whole return air system, not that an open duct should be placed at the point the HRV connects.

And the verbiage below the diagram has nothing to do with the ducts or the return air. It is related to installing an automated damper inside the HRV to close off the outdoor intake when the unit is turned off.

Screenshot (342)

My graphic from above. Same as the graphic from the manual, just a bit more detailed.


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Jumped the gun. Thanks Ryan. However as far as the option of installing a motorized damper, I understand it to be between the unit and the furnace’s return air ductwork …
"If the HRV is installed such that the homeowner may turn off the HRV during the winter, we recommend installing a motorized damper between the HRV’s supply air and the furnace’s return air duct that closes when the HRV is not operating "

The manufacturer likely words it that way to allow for different arrangements, but at least in my area, the exterior intake damper is always in the unit itself (as shown in the diagram below at the red arrow). The exterior exhaust for the HRV gets a damper at the exterior termination hood (orange line). This damper closes by gravity when the HRV is turned off.

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Attached is a pic of a breather tee along with some info as to its purpose.

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Thanks again Marcel. SO between this information & the tech’s inspection sticker, it would be safe to advise that the unit was observed to operate using regular controls and that no anomalies were observed but given the last service call, (11yrs) it is advised to have the unit serviced and checked by an HVAC professional.

And I don’t think that it was balanced…that sticker doesn’t say the company / technician name, cfm in and cfm out.

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Oh… come on. Everyone knows ‘YC.’ He’s a good guy… you can trust him.

That is a whole different installation method than what the OP has (at least as far as he’s identified anyway). That is for use with a HEPA system when combined with an HRV in a fully dedicated system. The OP’s scenario is not a fully dedicated system, and doesn’t have a HEPA system as far as he’s indicated. The OP’s system does not require a breather T because it is hooked to the return air system, which is open to the home in various places.

I don’t know what system the OP is talking about aside from the ventilator make and model; I was commenting on the open duct he was pointing at and it’s possible purpose.

I’m assuming a partially dedicated system (HRV pulls straight from interior and pushes into return air), or a return/return system (HRV pulls from and pushes into the return air), based on his initial post. But yeah, hard to know for sure without more pics.

Hey Ryan, No clear pictures available as it was so tight in there, I had to imitate Gumby to get back there to get a clear look but I can confirm that the HRV pulls from and pushes into the return air.

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