Fresh air intake

[Tom7227]

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

[PurpleFloyd]

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

[Tom7227]

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.

[Hoey]

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. 

[Moon Lake Refuge]

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.

[Walleyehooker]

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.

[swamptiger]

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 May 5, 2017 by swamptiger

[PurpleFloyd]

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?

[swamptiger]

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....

 

 

 

 

 

 

[RebelSS]

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.

[PurpleFloyd]

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. 

[swamptiger]

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.

 

 

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

[Grainbelt]

You could also j-hook the end of the duct and have no bucket.

[Walleyehooker]

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.

[Pat K]

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.

 

[swamptiger]

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....!!

[leech~~]

BUMP!

[Tom7227]

Project is finished.  I kept it.

[CigarGuy]

Wondering if any of you hvac guys can help me out. Have a 1600sf lakehome, two story, with a heated crawl space. Had an upflow gas furnace installed in the crawl space and it took a dump. Last year had a new down flow furnace installed in a laundry room that is about 6x14. All the duct work is in the crawl space, I had them cut a vent in the duct work to help add some heat down by the plumbing. The HVAC guy had me close off all the return vents and I'm only get fresh air to the furnace through the side of the furnace in the laundry room, have a filter cut into the side of the furnace. When I turned on the heat last winter for the first time, you could feel the air imbalance just pulling the air towards the laundry room/furnace. It was pulling air so bad that it was sucking it from outside. I had a couple of interior water lines that froze. Closed off the vent we cut out in the crawl space and that improved the air imbalance pretty good- also added a bunch of insulation between the first and second floor. This new furnace 95% efficient 3.5 ton. My main concern is that the furnace runs about 7 times per hour. 3 or 4 times it will start up, run for 3 to 4 minutes, shut down and immediately the blower will come back on-clear the line and the furnace kicks back on for 4-6 minutes. Questions:.    1) is this a normal or sufficient install, closing of the return vents and only getting return air through the laundry room?   2) is it normal for these new high efficiency furnaces to run that often? I've talked to other's that have had new high efficiency furnaces installed and nobody's turns off and on that many times. Trane/American Standard doesn't have a technical support line, which is ridiculous. Any thoughts would be appreciated. Thanks..

[leech~~]

Not an HVAC guy but know enough that every room with a heat inlet should have a return as well to balance the house pressure and get good heat flow.  

Where is the thermostat located?  Also, wondering if it's running so much if its a big enough unit for the space?  

[CigarGuy]

2 minutes ago, leech~~ said:

Not an HVAC guy but know enough that every room with a heat inlet should have a return as well to balance the house pressure and get good heat flow.  

Where is the thermostat located?  Also, wondering if it's running so much if its a big enough unit for the space?  

Thanks Leech... I thought it wasn't right closing off all the return vents in each room that has a heat vent. He said he's done it several times and hasn't had any issues. I should add that I don't have any heat ducts on the second level, if that matters. I'm pretty sure the furnace size is ok. I've read that too big of a furnace can cause it to run more often than it should. Thermostat is centrally located on the main level. He's coming out Wednesday for the second or third time to try to figure it out. I've checked him out as far as his knowledge and experience, no red flags were raised.

[leech~~]

In my buddies dlb wide Mfg home he had for a cabin they had return cold air flow vents in each room above the door through the wall.  His setup was kind of like your's with only one return at the furnace but each room could return the cold air to the main living room which the furnace was located off of as the hot air register blew it in to each room.  If you have closed off bedrooms and bathroom I just don't see how your getting good flow or pressure flow if he's only got the hot air register blowing into it?  

Is the second level used for living space or bedrooms?  You could always put some vents through the floor and let the hot air rise up through it.  I know one old farm house I use to hunt out of only had vents in the ceiling going to the second floor but they heated with wood from the basement level.  Hotter then Helll up there though with all the heat rising up! 

[CigarGuy]

On the main floor is the entry, living, dining, kitchen, bathroom, bedroom- with large walk-in closet. Also, open stairs going up to 2 bedrooms, bath and sitting area. I leave all the doors open on the main level and close off the two bedrooms upstairs when nobody uses them. Plenty of air from all those areas to reach the furnace...I think

[delcecchi]

Not a HVAC guy by any means, but where does the combustion air come from?    Maybe you said, and I just didn't see it.   

 

I think the way it works is the furnace is triggered by the thermostat and runs for a set period of time.   Then it shuts off, perhaps due to a temperature sensor on the plenum or maybe just a timer in the thermostat.    After a period of time, if the thermostat is still calling for heat it will cut on again.     This continues until the thermostat is no longer calling for heat.   

 

The fan that circulates the air runs on a different algorithm, probably as long as the plenum is hot.   

 

This may be totally off so if it is, I would appreciate knowing how it works.   

 

There also could be some sort of flue draft sensor so if the combustion gasses aren't going right it shuts off the furnace, due to the pressure inside the house being too low compared to outside.

[CigarGuy]

The HVAC guy came out and checked it out again. He suggested opening up one of the cold air returns that I sealed off and he's going to come back and run another return off the furnace down into the crawl space to supply more fresh air. Also, wants me to buy a new thermostat. Because it's a down flow furnace, the hot air wants to rise up towards the furnace, he thinks that might cause it set off a sensor, causing it to cycle more often, he's going to check that thought out with a tech guy and get back to me.