What is going on here?

This was in a home built in 2003 in Lake Worth, Fl.
It is a fresh air intake from the exterior into the intake line which is in the garage.

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Seems like a make shift Radon mitigation system.

Could it be for a HRV(Heat recovery ventilator) or ERV (energy recovery ventilator)?

Is this a Cat 4 furnace and do you have any pics showing the other end?

We don’t have Cat 4 furnaces here in S Florida…hell 1/2 the houses don’t have ANY type of heat.

Well he did say air intake and this is the HVAC section.
Maybe he meant makeup air to closet.

It is an electric, 3 ton split system air conditioning unit.
The line is, as you can see, metal and not insulated. The box, which is above the soffit, goes to a vent outside.
The homeowner stated that this was a new requirement when the home was built.

It is for make-up air that runs through the attic, down through the garage ceiling , and into the return plenum, which attaches to the stand the air handler sits on and then goes through the ceiling and connects with the other return registers in the bedrooms. There is also a damper right where the line connects to the plenum.

I am assuming that the box pictured is some type of filter so that unwanted odors do not enter the home.

I couldn’t tell if condensation was building up which caused the sheathing to rot, or if it was from a roof leak.

If the hot air from the outside can get in, what is to prevent the cold air from the home to get out?

I doubt very seriously that the local AHJ requires outside make up air but on the other hand anything is possible.

Don’t assume anything the box pictured probably has no filter just a square transition from the round duct to allow a square grill in the soffit.

All duct work associated with the central systems are required to be insulated in non-conditioned spaces such as attics.

You last question tells me that HVAC is not your high suit and that you do not understand the system as a whole. I am not trying to be nasty here but some good advice would be to do some serious reading on the subject

I thank you for your reply, most of it.
I am posting this because it is something I haven’t seen in 22 years of performing inspections.
Trust me, I am well aware of how the system works.

I am also well aware of the code requirement for insulation (R-4.2) in an enclosed attached garage, which is where this line is located. I sent that along with another code reference

Which would imply, that there is a possibility that make up air from the exterior is allowed.

If you have anything, constructive to add, please do so.

I don’t know if it is constructive or not but I REALLY STRUGGLE with the last question you posted as to your understanding of the system as a whole. Nuff said

As to make up air of course it is allowed from the exterior of the home just restricted as to where it can be taken from. Normally not required as 10% of make up air into a home is obtained through doors and windows

I’ll enlighten you as to the last question. Here , on new construction, it is required that there is an intake in each room for make up air in addition to the main intake. This is tied into a box in the attic, in this case, in the middle of the hallway. This is also the filter location. There is a 16 inch line that runs to another box in the garage, which extends through the garage ceiling.

The fresh air intake line goes from this box, in the garage, through the garage ceiling, and this is the line that exits the building through the box shown.

So, when the system is off, what is to prevent the air that is in the rooms, to go through the duct work for make up air and then out of the home?

I will be gracious enough to assume that you meant that I was referring to air in the system, going backwards, through the cooling coils and then out of the building.
That may be possible, but highly unlikely. It wasn’t what I was referring to with the comment you are referring to.

As to a filter, what I was referring to was some type of odor arrestor. Where the vent is happens to be on the side of the home where an ally is. Which is where all of the others place their garbage for pick up. There is also a neighbors house right near the vent. Unwanted odors may enter the home.

Although this may be required by the code, and I have a call in to the building department regarding the installation, I wouldn’t want it in my home.

Correct me if I misread something but it appears the original post is all about a portion of the return air being drawn in from the exterior.

This is typical on energy star homes or homes built with attempted energy saving methods. Research is being done to change the standards since the big savings are not being achieved so far.



why is it that I’m getting the inclination that you’re talking out your ***! ?

why do you have to insulate a fresh air intake that is working on the same temperature as that in the garage?

I’ll enlighten you, you don’t know what your talking about.

If you knew what you’re talking about you wouldn’t be posting the question.

We all know what this is, you obviously don’t.

Who assigned you to be in charge over the authority having jurisdiction (AHJ)in Florida?

I can only surmise that you played with HVAC equipment for a portion of your life.

If that chunk of metal pipe you showed us from the attic enters into the garage, I’d be more concerned about it not being fire rated!

Go ahead and call the AHJ and show them just how stupid the rest of us are.


you’re the one that knows exactly what’s going on! It doesn’t matter how big of a hole you have in the side of your house if there is not a difference in pressure between the inside and the outside the air will not flow. need I remind you of this?

It appears that you’re making some sort of assumption without any documented testing results. What is the pressure differential of the building? Where is the neutral plane within the building?

With this type of system installed it will generally create positive pressure in the building (in most circumstances). What is the pressure of the building? Or did you actually evaluate that?

You ask us to evaluate which you have not evaluated. We cannot give you a definitive answer unless you provide the necessary data.

I won’t bother with most of your response. What I will say is that I took my ladder, climbed on it and put my hand next to the exterior vent while the system was off.
Guess what I felt? Air coming out of the vent.
Do you have any plausible explanation for this?
Or, are you just an asshole?

I stated that I have never seen this. As another poster stated, there is some question as to the advantage or more appropriately, the lack of it, to having fresh 100+ degree air introduced into the a/c system.

You can pour yourself a big cup of STFU any time now!

You are exactly correct.

There are a lot of *** holes here. Why should I exempt myself?
There’s not enough room to list them!

Oh wow! That’s scientific!
Have you ever happened to hear about Air Mixture calculations?
But of course not.
Gather the proper information and you can get the proper answer.

If you weren’t such a smartass, You could perform the calculations and answer your own damn question.

I have no problem with questions, but you come off as a smart *** to others responses.

If you provide the proper information I could comment on it! Did you gather this information? Think not!

yup, and you can do the same!

If you can’t document the facts, just shut the fark up!

If you don’t do the damn job, why waste your time commenting on it?

We have no earthly idea what’s going on down there!

Some people here that have more time in the ****z House than you have experience, have tried to answer your question. Why don’t you just shut the fark up and listen?

What is the explanation for the air coming out of the house?
It was a steady stream. There is no need for an accurate measurement of air flow as is doesn’t make much sense to have the air in the home coming out of the home.
If it did, we would just open all the windows and run the a/c.

The only smart *** remarks I made were to the poster who didn’t want to be “nasty”. By making the post he was. Just like when someone says “with all due respect” something disrespectful is about to be said.

If you do not have anything of value to add, please do not waste your valuable time responding.

And your the one to make this determination?

I would say that is for you to determine. Did you?