Introducing Attic Air into HVAC

(Terrill Ewald, CPI, MD# 31310) #1

Is it common practice to pull “Fresh” air (100+) degree from an attic into the HVAC? It would seam to me that it would make the AC run a lot harder to cool the air. Not to mention pulling the insulation dust into the unit.

(Chuck Evans, CMI TREC 7657) #2

In many “tight” homes, they introduce “fresh” air from the exterior of the house into the return, usually through a damper controlled duct and filter (I see yours is filtered). I would document any open return or supply in a vented attic as a deficiency.

(Terrill Ewald, CPI, MD# 31310) #3

That’s the main HVAC filter.

(Dave Fetty, CMI) #4

No, internet search the the units model number… “Carrier 1234xyz installation manual” for definitive answer regarding that unit.

(Erik Schmidt) #5

You need the manufacturer to say that what found is wrong, wrong, wrong. You have all the proof in your pictures. Air intakes tied to the return are for fresh air, ie, good air to replace stale indoor air, an attic is not going to provide clean fresh air what with all the dust never mind loose insulation.
An air intake for combustion air is used for burning fuel, so that conditioned air is not sent up the chimney. Furnaces prefer clean air as well, so whatever the intake is being used for, it is in a bad location.

(William B. Ogletree, TREC License #22530) #6

I agree with Erik. Attic air is not fresh air. As you accurately observed, it is much warmer than outside air (in the summer, at least).

Not sure how long the attic stays “hot” in Maryland, but in Texas it’s the majority of the year, so this arrangement would definitely not be efficient here.

Just for my own edification, can you guess as to why the system is set up to pull in fresh air? When I see such systems, they are usually installed in homes utilizing “full encapsulation”, where foam insulation is applied to the underside of the roof sheathing and the inside of the soffits, effectively sealing the attic away from outside air. That would make the intake in the attic doubly wrong.

(Marcel Gratton, CMI) #7

It’s a poor’s man HRV. That air intake should extend to the outside. I have a document that explain its purpose but is too large to upload here. Send me your email and I will send it to you.

(Kenton Shepard, CMI) #8

Terrill, is that a combustion air supply duct or a return air duct?

(Terrill Ewald, CPI, MD# 31310) #9

Return air duct. Supply and Exhaust are PVC

(Dominic DAgostino, CMI HI3957) #10

I don’t think you understood the question…

(Erik Schmidt) #11

Fresh air intakes have been required by code in Alberta Canada since before I was installing furnaces in the late 1970’s. Up here homes are shut up tighter than a bugs butt for about 7 months each year, not because its so hot :-).
Intake brings fresh air from outside into the return air duct, this pressurizes the house slightly so that air leaks out instead of in, and brings in needed fresh air to replace stale air.
Before 2010, when we still used furnaces with chimneys, there was also a combustion air intake, so code required two air intakes, one for fresh air, one for combustion. Since 2010 the only furnace we can buy in AB are condensing types with direct venting, so new homes only have fresh air intakes anymore.
Code upgrades continue to require greater construction tightness for energy efficiency, so fresh air intakes become more important. Since about 2000 new homes are required to have mechanical ventilation, furnace fan and an exhaust fan are connected to a switch, turn it on and both fans operate, furnace fan brings in fresh air through the fresh air intake, and exhaust fan gets rid of indoor air. That meets minimum code requirements. A higher end solution is an HRV (heat recovery ventilation) that exchanges the heat of exhausted air with the incoming cold air.