Cool air entering room from return
Can anyone help me out with some ideas/suggestions? I'm not an HVAC professional, but have a mechanicial background and a cursury understanding of the basic operation (at least I think I understand).
This is our second winter in this home. Last winter the home never was warm, we spent over $4000 in oil but never got the chill out of the house. There were time that I could feel a cool breeze in the living area and my repeated attempts to find it were unsuccessful.
This fall we installed a wood burning fireplace insert and that has helped immensely with keeping the house warm, however I'm feeling that breeze again. In the living room there is one main HVAC return vent for the entire first floor. Late one night (2am) the breeze was driving me crazy and I tracked it to cool air coming into the room through the return vent.
I have since taped a small strip of tissue paper to the vent so I can see when air is entering the room. At first I only noticed it after the wood buring insert had been running several hours, so I assumed what was happening was the heated air was rising to the second level of the home and displacing the cool air, thus forcing it down the return ducting. However, this morning the fire place wasn't running and I again noticed cool air entering via the return vent.
I don't think this is outside air, but in all honesty I don't know. It hasn't been below freezing since I noticed this vent issue, but from feeling the air I would say it is not from the outside...maybe the basement, upstairs or even the attic (where the upstairs ducting runs are located). But in all honesty I don't know for certain, so it very well be entering from the outside.
I've had a well respected local HVAC outfit here a few times for different things, and no one has noticed anything unusual about the system.
Does anyone have any suggestion/ideas? Any input is greatly appreciated.
The entire Return-Air system needs to be thoroughly checked.
Many times there are air-leaks allowing outside air to enter the Return.
Is there anyway the Return Run could allow outside air into the Return?
That could also explain why the heating system couldn't keep you sufficiently warm, & ran-up a huge heating bill...
A home energy efficiency rater/audit could find many sources causing the heating problem...
having a duct blaster test performed is the best way to know if the ducts are compromised
If this is a newer home you could have a fresh air makeup attached to the return side of your unit for dilution purposes if the house has a tight design
The return air vent where you feel the cold air coming from - if I read you right it is located downstairs in your living area. Is it low on the wall, high on the wall, or in the ceiling?
Does the HVAC that this return vent is connected to reside in the attic, basement, or crawl space?
One thing you can try immediately is this: remove the grill covering the return where you feel cold air entering the room. Do you see any kind of ducting material behind it, such as a sheetmetal box? Or does it just look like part of the house construction?
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
If this is an older multi storied home you could simply be experiencing siphoning of air due to the different air temps within the home. As the warm air rises to the upper floors (from wood unit), the cooler air is coming back down thru the return system ducting. But if I was you, I'd contact a contractor with a blower door testing device and have your home checked for tightness. Might heat a lot better if sealed well. I assume you've already insulated the house real well?
what exactly is a duct blaster test?
I don't think it is outside air because the main return ducting runs through the center of the house, from the basement to the attic. In the attic is splits into two (one for each zone) one in the main hall and the other in the master (both cool areas).
Originally Posted by udarrell
This sounds like a feasible thought, because the temp of the air is pretty cool. However, the house it 12+ years old and is not tight. I've not noticed a separate duct/line running to the unit from the outside. But maybe I'm looking in the wrong spot. If there were a fresh air makeup, where could it be located? I've looked over the the entire system pretty thoroughly I don't think there is one, but I'll look again.
Originally Posted by second opinion
Yes, the return is a large (approx. 24" square) grill located high on the wall (approx 9') in the main living area and serves as the return for the entire first floor (approx 1500ft).
the return ducting is in the center of the house and runs from the basement to the attic where it splits to two other zone returns, one in the main hall and the other in the master bath (both fairly cool areas). I've looked over the ducting where I can see it and it looks to be intact.
I removed the grill and for as far as I can see it is line with some sort of insulation (black blanket type) so it's difficult to say if it is sheetmetal behind the blanket. My guess is that it is sheetmetal as the duct from the basement goes up into that wall and then exits into the attic and appears to be all sheetmetal.
Originally Posted by Shophound
This was my original thought as well. That as the hot air rises it's displacing the cooler air upstairs and forcing it down the return ducts. But I'm not so sure that is the case. The room the main return is in is certainly warmer than upstairs so considering this theory, wouldn't the warm air rise into the return? And the other day the wood stove hadn't been running, so the temps throughout the house were probably fairly consistent, and the cool air was blowing in through the vent.
But there is certainly more pressure in the return duct than the living area as the cool air just flows right in. I checked to ensure that the blower isn't running and there are no fans running in the house.
Originally Posted by wahoo
Cool air from return
Thanks for all of the input.
The house is two level, plus a basement and is absolutely not tight, we have a catherdral ceiling in the main living area with can lights which cold air flows freely. We have four bay windows each with can lights which flow freely and on top of that most of the windows in the house are ~15 years old and low end. The insulation can definitely be improved upon as well. These are all projects that I intend to eventually get to but for the time being they'll have to do.
Most can lights leak air horribly. Hopefully you don't also have shredded blown fiberglass insulation also! That's without a doubt the cheapest and worst insulation you can have!
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