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HVAC Makeup air. #5404735 04/16/20 08:04 AM
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JustinH Offline OP
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I have a house built in 2019 by Lennar.

It has a typical gas furnace and Lennox AC system.

I notice some cold fresh air blowing in the return air vent in the ceiling when the system is not running.

At first I was thinking it was a duct work leak. However everything seems tight and no tears.

Now I am reading that some new houses have make up air added to the system because they are so tight, it keeps stale air out.

I noticed that the ducts always seem pressurized, when I change the filter media, I can feel air moving through the system, with the system off.

Is it common for residential systems to have make up air? What would I look for to see if I have this?

I wanted to ask on here before I opened a ticket for the warranty company.


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Re: HVAC Makeup air. [Re: JustinH] #5404765 04/16/20 08:26 AM
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BMWTurboDzl Offline
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You would want to look for a small duct run w/damper leading from the outside to a return. Try the furnace area first. In addition the paperwork for your home should state whether or not you have a ventilation system.

This is commonly called "supply only" ventilation and since the supply duct should have a damper attached you should only get ventilation when the blower motor is running.

If you're feeling air when the blower motor isn't operating then it's possible that there's a disconnect/tear in the duct or the damper isn't working as intended. Inspection of the damper and/or pressure testing the duct system is the only way to know.


example

Last edited by BMWTurboDzl; 04/16/20 08:32 AM.

“It took untold generations to get you where you are. A little gratitude might be in order. If you’re going to insist on bending the world to your way, you better have your reasons.”

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Re: HVAC Makeup air. [Re: JustinH] #5404780 04/16/20 08:43 AM
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Donald Offline
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If your house is super tight you need a true air to air heat exchanger to bring in fresh air and push out stale air. It pulls the heat from the stale air and gives it to the fresh air.


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Re: HVAC Makeup air. [Re: Donald] #5404787 04/16/20 08:47 AM
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BMWTurboDzl Offline
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Originally Posted by Donald
If your house is super tight you need a true air to air heat exchanger to bring in fresh air and push out stale air. It pulls the heat from the stale air and gives it to the fresh air.



Balanced ventilation via dedicated duct system coupled with a HRV/ERV isn't common in the warmer and/or humid climates.

Supply-only systems generate positive pressure which forces stale air out through small cracks in the home. Production built homes, while tighter than previously allowed per code, are no where near passive house levels of air tightness.

Last edited by BMWTurboDzl; 04/16/20 08:50 AM.

“It took untold generations to get you where you are. A little gratitude might be in order. If you’re going to insist on bending the world to your way, you better have your reasons.”

435i
Re: HVAC Makeup air. [Re: JustinH] #5404837 04/16/20 09:15 AM
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Fitter30 Offline
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There is a test for how tight a house is called a blower door test. Where they set up a fan in the front door and seal the doorway off fan pulls air out of the house and measure cfm vs a certain pressure. Some electric utility companies offer this test in part of a energy audit. My co op charge $50 and gave me more than $50 of stuff light bulbs to caulking.

Re: HVAC Makeup air. [Re: JustinH] #5404923 04/16/20 10:20 AM
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thooks Offline
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It's not a bad thing. You could get a competent mechanical contractor to install a motorized damper in the outside air duct that is interlocked with your evaporator fan to open when the fan is on, closed with the fan is off. This would be the best, cheapest solution.

Re: HVAC Makeup air. [Re: JustinH] #5404926 04/16/20 10:24 AM
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Reddy45 Offline
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You should still open a ticket so a tech can come out and show you the system. At some point in your ownership you'll need to maintain whatever is bringing in fresh air. It could be a ERV tied into your HVAC system, or at the least a passive filtered duct connected to the return side plenum.

Re: HVAC Makeup air. [Re: JustinH] #5404928 04/16/20 10:27 AM
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CourierDriver Offline
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The only time we ever installed a makeup air intake was in beauty shops to remove all that dye smell and chemicals they use,,,,,We never put make up air in residental homes,,,never, in Tn or Florida...call a Technical school that teaches HVAC in your area and ask them about that.


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Re: HVAC Makeup air. [Re: JustinH] #5405029 04/16/20 12:43 PM
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Make up air is also used at restaurants due to ventilation hoods sucking out cooking smoke. They balance that make up air in the system by measuring differential pressure in the bldg and getting it near zero. I don't believe there is ever a need to have make up air on a normal house. If you're feeling air movement with the blower off something is wrong.

Re: HVAC Makeup air. [Re: Kawiguy454] #5405074 04/16/20 01:37 PM
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BMWTurboDzl Offline
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Originally Posted by Kawiguy454
Make up air is also used at restaurants due to ventilation hoods sucking out cooking smoke. They balance that make up air in the system by measuring differential pressure in the bldg and getting it near zero. I don't believe there is ever a need to have make up air on a normal house. If you're feeling air movement with the blower off something is wrong.



Residential Ventilation is found under ASHRAE. You don't see it because the vast majority of locales don't make it part of their residential building code.

Ventilation only becomes an issue when building codes are updated to reduce energy usage. Reducing the amount of air leaks within a house is one way to reduce energy usage, however when that reduction reaches a certain point mechanical ventilation is required.

There's a ton of push back on this from state/regional homebuilder associations in areas which have cheap energy and/or mild climates. They don't want to deal with the added expense and since homebuilders have input on code adoption these requirements never get adopted to the revised code.

Supply-Only ventilation is literally the least-worst method to provide some sort of ventilation to a well built house.

Last edited by BMWTurboDzl; 04/16/20 01:42 PM.

“It took untold generations to get you where you are. A little gratitude might be in order. If you’re going to insist on bending the world to your way, you better have your reasons.”

435i
Re: HVAC Makeup air. [Re: JustinH] #5405322 04/16/20 05:40 PM
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An ever present issue with tract homes is inadequate return air. My house was built in 1996 (General Homes) and until I built a return air plenum and added an additional air return to the unit my system was unable to maintain a consistent temperature throughout the house. My single filter looked like an inverted bowl and the air return sounded like a vacuum cleaner. The first step is to ensure that you have enough return air volume. Everything else is secondary. A GOOD HVAC contractor can help with that. I was a facilities manager when I added my extra return and I asked one of my HVAC contractors to calculate the required total duct diameter for me.

Re: HVAC Makeup air. [Re: JustinH] #5405421 04/16/20 07:37 PM
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It is required by code to have fresh air if the house is built too tight or make up air if the kitchen exhaust pulls out too much air. I know people that disable them after the final inspection because in Florida it causes problems with bringing in too much humidity during hot months. It is normally located in the return duct and should have a damper in it, we normally use metal pipe or aluminum thermofin flexible duct, the stuff they use for bathroom exhausts...just to give you an idea.

Last edited by laserred96gt; 04/16/20 07:40 PM.

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Re: HVAC Makeup air. [Re: laserred96gt] #5405988 04/17/20 12:46 PM
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Originally Posted by laserred96gt
It is required by code to have fresh air if the house is built too tight or make up air if the kitchen exhaust pulls out too much air. I know people that disable them after the final inspection because in Florida it causes problems with bringing in too much humidity during hot months. It is normally located in the return duct and should have a damper in it, we normally use metal pipe or aluminum thermofin flexible duct, the stuff they use for bathroom exhausts...just to give you an idea.


I'm not surprised. I'm sure builders aren't requiring dehumidifiers to account for this during the shoulder season.


“It took untold generations to get you where you are. A little gratitude might be in order. If you’re going to insist on bending the world to your way, you better have your reasons.”

435i
Re: HVAC Makeup air. [Re: laserred96gt] #5408532 04/20/20 09:52 AM
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JustinH Offline OP
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Originally Posted by DBMaster
An ever present issue with tract homes is inadequate return air. My house was built in 1996 (General Homes) and until I built a return air plenum and added an additional air return to the unit my system was unable to maintain a consistent temperature throughout the house. My single filter looked like an inverted bowl and the air return sounded like a vacuum cleaner. The first step is to ensure that you have enough return air volume. Everything else is secondary. A GOOD HVAC contractor can help with that. I was a facilities manager when I added my extra return and I asked one of my HVAC contractors to calculate the required total duct diameter for me.

Originally Posted by laserred96gt
It is required by code to have fresh air if the house is built too tight or make up air if the kitchen exhaust pulls out too much air. I know people that disable them after the final inspection because in Florida it causes problems with bringing in too much humidity during hot months. It is normally located in the return duct and should have a damper in it, we normally use metal pipe or aluminum thermofin flexible duct, the stuff they use for bathroom exhausts...just to give you an idea.


Spoke with the builder this morning. They advised my Lennar home has a fresh air intake system that runs periodically to bring in fresh air. I took a look it is a little air pump near the handler that runs on a cycle to pump in outside air. He says I can unplug it if I want, but I'm going to leave it on.

Also tract houses have come quite a way with HVAC systems. I had a DR Horton house in Austin built in 2011. That thing had a 1 inch filter on it and one return air. The new Lennar house built in 2019 has two large return air vents connected to a 4 inch media filter, and this fresh air system. It came with a manual J printout when we purchased the house and it certified for a certain level of efficiency.


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