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-   -   Where to attach Fresh Air intake location on return plenum (http://www.diychatroom.com/f17/where-attach-fresh-air-intake-location-return-plenum-157783/)

Haggis 09-23-2012 10:52 PM

Where to attach Fresh Air intake location on return plenum
 
80% downward blow American standard Furnace in Calgary. Looking to move the location of where the fresh air enters the return air plenum to make better use of a tight space. Straight downward insulted 5 inch flex pipe from roof intake. Is there a Code distance from furnace burner? Is the plenum at negative pressure i.e. will it always suck the air in. I'm concerned that returning air would go up the intake, if I choose the wrong location. Ideally my preferred location would be about 4 foot before the burners. Any thoughts from helpful folks out there?

Missouri Bound 09-23-2012 10:57 PM

Are you looking to supply combustion air? If so, it needs to be on the supply, not the return. Or are you talking about something different?:eek:

beenthere 09-24-2012 04:27 AM

Are you talking about a fresh air intake, or a combustion air intake. Fresh air goes to the return plenum/duct, which is always a negative pressure when the blower runs. Combustion air intake terminates near the equipment.

DannyT 09-24-2012 08:15 AM

read the title of the post

Missouri Bound 09-24-2012 08:40 AM

Quote:

Originally Posted by DannyT (Post 1016302)
read the title of the post

:eek: Yeah, we read it and offered something constructive. Now it's your turn:smartass:

techpappy 09-24-2012 08:58 AM

So, Haggis..you state that you have a fresh air intake that you would like to move from it's present location where it is connected to the "return" air However you also say you would like it to be 4 feet from the burners..so, it is a little confusing.. It sounds like you may have a round duct from outside to be intended to aid combustion OR it is simply for fresh air for the house in general, in which case it can be attached to any part of the return air duct(s)...Combustion air duct usually is just a 4 or 5inch piece of round duct coming through the wall from outside and terminating near the furnace..quite often this has a couple of elbows attached to the end near the furnace to prevent excess entry of outside cold air but allows for required air to be drawn in when burner is running..I have never heard of this air coming via the roof area but then it may..especially if you are on a slab and don't want to penetrate the wall. BTW the return air plenum is only at negative pressure when the fan is running otherwise it can vent to outside when not running..hope this is helpful

beenthere 09-24-2012 04:41 PM

Quote:

Originally Posted by DannyT (Post 1016302)
read the title of the post

The OP has posted info that implies he may be trying to convert a fresh air intake into a combustion air intake.

I read more then just the title.

techpappy 09-24-2012 05:07 PM

yes Been there ..I agree that's why I explained what I did in the hopes the OP would clarify

So OP..we would like to know what you are trying to accomplish here OR if you already have your answer..would be nice to know..
THANX Techpappy

beenthere 09-24-2012 05:10 PM

Quote:

Originally Posted by techpappy (Post 1016590)
yes Been there ..I agree that's why I explained what I did in the hopes the OP would clarify

So OP..we would like to know what you are trying to accomplish here OR if you already have your answer..would be nice to know..
THANX Techpappy

I was explaining my response so DannyT would know I read more then just the title.

Missouri Bound 09-24-2012 07:50 PM

I"m hoping Haggis comes back...now I am not sure what his intentions are. It appears he wants to introduce fresh air into the system rather than supply combustion air. Is this what everyone else thinks?:eek:

beenthere 09-24-2012 08:30 PM

I think the OP is confused on how fresh air intakes work, and what they do and are for.

Haggis 09-24-2012 09:30 PM

Getting Fresh!
 
Thanks for all the input lads/lass'. Bit cheeky from Danny T! Beenthere - I'm mostly confused why Albertan drivers only use one lane on highway ramps when there is two - maybe too stressfull to do that alternate merge thing at the top/bottom of the ramp... but there is a reason why there is TWO!
Missouri and techpappy are correct. This is 100% a fresh air intake query - not combustion air. Both intakes are 5 inch flexible insulted pipes; one ends in a pot at the furnace the other enters return plenum at about 7 foot from burners. Furnace location is not against outside wall so flex pipes are floppin across an interior wall to the exterior wall. Much tidier if I can bring everything straight down from roof, through ceiling. Soffit option is too tight.
Negative pressure is good so I can attach intake at the end of the plenum before air goes into furnace unit. I had read something about cold air cracking the furnace but I'm assuming any -30 celcius (-22F in old money) air will be well diluted by returning air. I'll just do a simple 90 degree join; 5 inch flex into plenum and cover up the old entry. Tidy! Cheers!

Missouri Bound 09-24-2012 09:44 PM

Thanks for getting back to the thread. Is there any chance at all you could post some pics showing the location of ductwork and where you plan to connect? You say there are two fresh air intakes, corrrect? It's certain you can clean things up a bit but they must remain seperate. The one which goes to the furnace (in a pot)can't be connected to the return air plenum. That one is for combustion air. Pics would help. Am I mistaken?:eek:

Haggis 09-24-2012 09:57 PM

Will attempt the photo attaching. For sure, both intakes will stay separate;1) combustion pot 2)return air plenum. Thanks again!

Haggis 09-24-2012 10:37 PM

Requires tidying..
 
3 Attachment(s)
You can see why I need to improve the arrangement! Will take better shots later - not at home till Friday. Had wife e-mail these. You can see the top of the return air plenum, behind rubbermaid bin sitting ontop of furnace. Downward blowing furnace. Will connect return air intake to top, after dropping down from ceiling. Not sure what to do with combustion intake yet, and I will have to replace ceiling components of exhaust chimney (welds cracking open). It has liner running up thru.
Aye.


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