Thread: fresh air intake

I've been noticing a frequent issue in the fresh air intakes for the newer HVAC systems. Some installers are using exterior hoods that have dampers meant for air to blow outward. They are leaving the damper installed instead of removing it from the hood. Thus, when the system calls for fresh air, the damper blocks the path for it to come in.

I just thought I'd mention it to give everyone a heads up.

These are known as economizers and open when needed. Depending on the system parameters these open when the temperture differential is in favor and / or to allow only so much fresh air in , also so the freash air port is not aways open

You can easily tell the ones we have here (FL) as they extend off the roof about 2' as to not take in too much hot air from the roof.

Originally Posted by Dwight Doane

These are known as economizers and open when needed. Depending on the system parameters these open when the temperture differential is in favor and / or to allow only so much fresh air in , also so the freash air port is not aways open

I have also seen improper vents used at least 4 times. John and I are smart enough to know these are not 'economizers', they are just regular hoods with metal 'flaps'. There is no way they can "open when needed". The last time was on an air-to-air exchanger with two vents out an upper gable. The hvac contractor called me personally to thank me, he said the flaps should have been removed and screens installed.

Originally Posted by John Dirks Jr

I've been noticing a frequent issue in the fresh air intakes for the newer HVAC systems. Some installers are using exterior hoods that have dampers meant for air to blow outward. They are leaving the damper installed instead of removing it from the hood. Thus, when the system calls for fresh air, the damper blocks the path for it to come in.

I just thought I'd mention it to give everyone a heads up.

I come across that often. Also, a clogged screen on the weather hood preventing fresh air entry.

Do you have pictures? Thanks!! Are you saying these are installed with the intention of being removed later or are just installed wrong to begin with?

Originally Posted by Tom Rees

Do you have pictures? Thanks!! Are you saying these are installed with the intention of being removed later or are just installed wrong to begin with?

On my way out, 7:30 here. Clothes dryers here at ext walls either have plastic vents with 3 louvers or metal vents with one metal flap. What I'm talking about is the type with the metal flap. I've seen these used for air to air and for intake air into the furnace.

Also- several times I've found ext intake air into a furnace with a little 8x8 filter in the attic (where the furnace is), rather than running the intake on the house side of the filter in the hall ceiling. Without a home inspection the buyers would likely never know they had an outside air intake and a small filter in the attic.

The intake on my home had the damper installed, similar to the one in the photo. I just popped of the screen and removed it. I could hear it whistle when the system was trying to pull air in.

Are we talking about combustion air ducts where the duct terminates in the mechanical room and supplies combustion air or on the newer high efficiency systems where air is brought in directly to appliance in sealed combustion chamber through PVC pipe (or both). I believe having a screened/filter cover on duct in attic is not allowed (correct me if I'm wrong). Randy, are you talking about return air in hall ceiling?

Found relevant photo, drilling a hole to install a vent:

Originally Posted by gary carroll

Found relevant photo, drilling a hole to install a vent:

Will you be using the same depleted uranium armor piercing round?

Originally Posted by Tom Rees

Are we talking about combustion air ducts where the duct terminates in the mechanical room and supplies combustion air or on the newer high efficiency systems where air is brought in directly to appliance in sealed combustion chamber through PVC pipe (or both). I believe having a screened/filter cover on duct in attic is not allowed (correct me if I'm wrong). Randy, are you talking about return air in hall ceiling?

Good questions. I was referring to the intake for the HRV (air-to-air exchanger) in my own home.

I also have a fresh air intake that goes into the return air duct of the HVAC system.

I guess the point being made here is that intakes should not have a simple flap dampers on them.

I see the damper flap left many times which I point it out to be removed and add a screen for make up air. They are multi use hoods. They also are installing a wind sock (for lack of better term) so when not in use it collapses.

Originally Posted by Tom Rees

Are we talking about combustion air ducts where the duct terminates in the mechanical room and supplies combustion air or on the newer high efficiency systems where air is brought in directly to appliance in sealed combustion chamber through PVC pipe (or both). I believe having a screened/filter cover on duct in attic is not allowed (correct me if I'm wrong). Randy, are you talking about return air in hall ceiling?

Neither. My original post refers fresh air intake. They are installed to introduce fresh air into the HVAC return plenum and distribute it throughout the house. With the new energy efficient regulations, the homes are getting tight enough they are installing managed fresh air intakes.

Originally Posted by John Dirks Jr

Neither. My original post refers fresh air intake. They are installed to introduce fresh air into the HVAC return plenum and distribute it throughout the house. With the new energy efficient regulations, the homes are getting tight enough they are installing managed fresh air intakes.

Hi John, Sometimes it's hard to understand exactly what posters are referring to. I don't see fresh air from exterior dumped directly into return air around here. What I generally see is the fresh air coming in and being conditioned with a ERV or HRV unit before entering the return air. Usually the only time I see this is on the more expensive homes. I will pay more attention to intake ducts now. Thanks for the heads up.

Good post John. I try to check for proper direction on HRV and fresh air induction. Although it is not a difficult subject, it is amazing the number of times I see it screwed up.

I found one where the fresh air induction duct was connected to the supply side of the HVAC system which effectively meant dumping the freshly conditioned air to great outdoors along with throwing the entire house into a negative pressure zone.

I regularly see improper vent terminations used on multiple systems such as dryer vents using a screened opening, fireplace combustion air inlets using dryer exhaust hoods, furnace/water heater room combustion air vents, as well as the ones you mentioned for HVAC ventilation.

It is kind of like the "think like a rain drop" for roof and flashing details except in each vent penetration you must first determine what is supposed to be happening in that particular vent and then "think like air" in both the on and off cycle.

Obviously, beyond the capability of some installers!