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Tom7227

Fresh air intake

16 posts in this topic

My house was built in about 1965.  I have a high efficiency furnace with a combustion air intake.  A power gas water heater without combustion air intake and a clothes dryer.  The house is being resided and I wonder if I need to have a fresh air intake.  Currently there is one and it is a sheet metal device that rises the intake about 18 inches from a cement surface.

 

Do I need to have that device, or something similar, reinstalled?  Does it have to be built so that it sits the 18 inches up or can it be 6 to 8 inches from the ground?

 

The house has decent double hung thermo pane windows,  It is relatively tight with 2x4 construction and an additional 3/4 inches of foam on the exterior of the house.  Typical fiberglass in the walls.

 

Does the code require the fresh air intake?

 

Thanks for your time.

 

Tom

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Do you mean a cold air return or an aftermarket air exchanger unit?

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Not an air exchanger.  Device on the outside of the house has a 6 inch flexible duct that leads to the floor in the basement.

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Anything gas operated consumes ambient air.  Without some sort of outside air supply or free outdoor air, you are relying upon some leaks in the building envelope, without it, you will develop a negative indoor air pressure that will impact combustion and exhaust.  Can be very dangerous.  There is probably building code for this.  

 

In my house, this is a 4" flex duct with an outdoor air hood (and bird screen) and it lays on the floor between the gas fired furnace and gas water heater. 

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I thought those were typically run to the floor next to the furnace as an outside air combustion source.  If its truly just a fresh air intake, personally I would just install a damper in it rather than removing it all together.  Close it off and see what happens but if you start seeing moisture problems one way or another, then you can just reopen it without having to cut in a new line.  

The combustion line used to be code in some areas(not sure any more).  As to the height off the ground, any intake should typically be higher rather than lower in case there are any heavier than air gasses that build up for any reason(i.e. sewer gasses) so that you aren't pulling them back in.

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I'm not sure its code but I wouldn't delete it. Mine runs from the outside wall to over by the furnace and hot water heater that is gas also. Might not be a big deal on older homes that had plenty of leaks but if your house is sealed up tighter now you should probably keep it.

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Posted (edited)

Leave it.  You need a fresh air intake for the gas hot water heater and clothes dryer.

 

The basement floor wouldn't feel as cold if you just run the fresh air duct into an empty 5 gallon bucket.  

 

 

 

 

 

 

Edited by swamptiger

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5 hours ago, swamptiger said:

Leave it.  You need a fresh air intake for the gas hot water heater and clothes dryer.

 

The basement floor wouldn't feel as cold if you just run the fresh air duct into an empty 5 gallon bucket.  

 

 

 

 

 

 

How long does that take to fill up with air before you have to drain it? Could he use a 55 gallon drum to give him more capacity?

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2 minutes ago, PurpleFloyd said:

How long does that take to fill up with air before you have to drain it? Could he use a 55 gallon drum to give him more capacity?

 

Depends on how fast the air is moving out of the house.  If you have the dryer going, and it is vented to the outside, not very long at all..

 

But if you aren't running any appliances, and the house is fairly well sealed, it takes considerably longer....

 

The idea of the bucket is to simply diffuse the air a little better and mix it with some warmer air before it hits the floor - it's an old Indian trick I learned a long time ago before the days of high tech air exchangers....;)

 

 

 

 

 

 

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An ambient  fresh air intake installed by a knowledgeable HVAC person will terminate in an insulated simple "air box".  These are made out of sheet metal, with insulation inside, and available thru most HVAC dealers.  And YES, you need a fresh air source. Pic is of my air intake airbox. 10" x10" by 28" tall. 6" round insulated air intake ductwork terminates about 6" or so from the bottom of box.

I insulated the round intake pipe with typical fiberglass wrap with plastic wrapping cover, because at minus tempos, it would frost up.....proof it was moving fresh air in. You can feel the air moving up out of the box when the furnace is running.

DSC03313.JPG

DSC03314.JPG

leech~~ likes this

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2 hours ago, swamptiger said:

 

Depends on how fast the air is moving out of the house.  If you have the dryer going, and it is vented to the outside, not very long at all..

 

But if you aren't running any appliances, and the house is fairly well sealed, it takes considerably longer....

 

The idea of the bucket is to simply diffuse the air a little better and mix it with some warmer air before it hits the floor - it's an old Indian trick I learned a long time ago before the days of high tech air exchangers....;)

 

 

 

 

 

 

Indians didn't have buckets  they used gourd canteens and they were darn happy to have them. 

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2 hours ago, RebelSS said:

An ambient  fresh air intake installed by a knowledgeable HVAC person will terminate in an insulated simple "air box".  These are made out of sheet metal, with insulation inside, and available thru most HVAC dealers.  And YES, you need a fresh air source. Pic is of my air intake airbox. 10" x10" by 28" tall. 6" round insulated air intake ductwork terminates about 6" or so from the bottom of box.

I insulated the round intake pipe with typical fiberglass wrap with plastic wrapping cover, because at minus tempos, it would frost up.....proof it was moving fresh air in. You can feel the air moving up out of the box when the furnace is running.

DSC03313.JPG

DSC03314.JPG

 

 

There you go - a plastic bucket would do the same job...

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I'm not sure its code but I wouldn't delete it. Mine runs from the outside wall to over by the furnace and hot water heater that is gas also. Might not be a big deal on older homes that had plenty of leaks but if your house is sealed up tighter now you should probably keep it.

 

Mine is also just J hooked at the end and I put some netting across the opening so the cat or anything else doesn't climb in.

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My son clamped  the fresh air vent  shut in his house because he thought it made the utility room cold. After a couple weeks he had a CO detector in his basement going off intermittently. He found out he was creating negative pressure in the house and the furnace and water heater were back drafting.

 

Hoey and Moon Lake Refuge like this

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1 hour ago, Pat K said:

My son clamped  the fresh air vent  shut in his house because he thought it made the utility room cold. After a couple weeks he had a CO detector in his basement going off intermittently. He found out he was creating negative pressure in the house and the furnace and water heater were back drafting.

 

 

Bingo....!!

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