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-   -   Added a new HVAC Run, low air flow.... (http://www.diychatroom.com/f17/added-new-hvac-run-low-air-flow-158563/)

Johnnyv84 10-01-2012 11:35 AM

Added a new HVAC Run, low air flow....
 
So on the weekend i added a new HVAC run to my upstairs master bedroom (older house and never had a vent up there before). I was able to run it up the inside of the wall but due to the sizing between the walls i had to use a 4" pipe and 3 bends to get it up there.

After all was said and done i noticed the air is definitely blowing up to the bedroom now but its not a very strong blow. I checked all my joints where everything connects and even taped them all (except for one bend at the very top that i just couldn't reach very well due to the tightness and not much room to work). Is the low flow of air probably just due to the fact its about a 16ft run with 3 bends and its only a 4" pipe?

Im gonna double check tonight to make sure that everything is tight and there are no air leaks (which im pretty sure there are none), but i just want know if it is infact due to the small pipe i had to use? combined with all the other runs currently in the house (which are all using the normal size pipes).

Thanks in advance.

techpappy 10-01-2012 12:18 PM

What do you mean by "bends"?....each 90 degree bend adds at least 5 feet to total length..so, yes, you are right..the length of run, smallish pipe AND bends equals ..a lot of pressure drop...it is what it is..should help to heat that room though can't tell how much..you may be able to install a booster fan down below to help the air flow..check at your heating supplier to see if they have one for that size of pipe and check required voltage and availability of electrical..should be minimal

Johnnyv84 10-01-2012 12:21 PM

Sorry, by bends i mean there adjustable bends so they can bend any which way that you need. 3 of these guys:

http://www.indoorcomfortsupply.com/P...s/Elbow_90.jpg

I never thought about a booster fan, i may have to look into that. Thanks!

techpappy 10-01-2012 12:41 PM

my point was How severely did you make the bends..the elbows you show can be bent from a few degrees to 90 degrees ..the less the bend the better..I don't usually think booster fans are the answer however should help in this case.

Johnnyv84 10-01-2012 12:46 PM

Quote:

Originally Posted by techpappy (Post 1021170)
my point was How severely did you make the bends..the elbows you show can be bent from a few degrees to 90 degrees ..the less the bend the better..I don't usually think booster fans are the answer however should help in this case.

2 of them are 90 degree bends

techpappy 10-01-2012 12:56 PM

Just as I suspected. Those two bends add a min of 10 feet to total length...plus the over all run equals large drop in air supply..but, not much else you can do so, booster fan will help..but, not sure how much

Good Luck! Techpappy

Johnnyv84 10-01-2012 01:06 PM

Thanks for the info!!!! How do the booster fan's work? hard to install? do they always run for when the furnace kicks in or do they have there own thermostat? ive just never heard of them before so i dont know how they work or how they would even know when to turn on. Thanks!

techpappy 10-01-2012 01:37 PM

They fit in the supply air run and some are designed to run continuously however you can have them run via a duct stat ( which I have just read are not very reliable)or interlocked with furnace blower motor power OR some times via the thermostat..all this depends on how your furnace and stat are wired..Also can be energized directly off electronic control board if so equipped..of course amperage tolerance of all switching devices should be compatable..I have never had to install one so, perhaps some other members here can comment.

The fans are typically very low amperage but will vary depending on make and model.

ben's plumbing 10-01-2012 05:58 PM

could you have used wall stack pipe....3/1/2 x10.....3 1/2 x 12....oval 3 1/2 x 6.....then get proper adapters to tie on the main trunk...?????? just my question..can't see the project..ben

beenthere 10-01-2012 06:54 PM

Wall stack or oval would be the preferred choice over a 4". A 4" is enough for a bathroom, but thats about it. You'll have a hard time getting much more then 40 to 45 CFM through it.

Johnnyv84 10-02-2012 09:51 AM

I'll have to take some pictures and post them up later for reference.


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