90 degree elbows and air flow

[norcim]

I recently had a new furnace installed and the installer used 3 extra 90 degree elbows in the return air drop. He did this because the old furnace had a rear return. The new furnace does not allow a rear return and it was easier for him to turn the return air drop than the furnace. He assured me as long as he uses radius elbows it would have no significant effect on air flow. Now I have a fan noise issue and they want to blame it on my existing ductwork which from what I've read is fine. What I'm wondering is how much air flow is lost when these elbows are used and could these turns cause turbulence across the fan and cause a high pitched whine.

[rimek]

This sounds good- please post a picture.

[docholiday]

Radius ells dont do squat unless the inside of the ell is also rounded, otherwise its just a plain ol ell.

Turning vanes would be better.

After saying that.... is the new furnace moving more air than the original one did? Or is it trying to?

[beenthere]

As Doc said, the inside has to be radioused also.

Can you post pics of the duct work.

Also the brand, and mod number of the furnace.

[norcim]

Thanks for the replies. The furnace is a 120,000 btu rheem #rgfd12ercms. I will post a picture as soon as I figure out how. The ells do not appear to be round on the inside. What are turning vanes?

[norcim]

Here is a picture In case you are wondering I put the brace under the duct because there is nothing else holding it up.

[Edited by norcim on 02-07-2006 at 08:54 PM]

[docholiday]

You're probably ok. Looks like hell. What is the black flex for?

[norcim]

fresh air

[Advanced Response]

120,000 btu Rheem 90% is it???

If it is I imagine you also have a 5ton a/c?? What size is the a/c??
Also model #'s of the equipment might help with additional pictures of the unit from differant angles..

I believe the size furnace you have requires a balance box or a return on each side of the furnace but we need more information and pictures to determine...

Good luck
J

Wow, that is alot of furnace,, I hope a load calculation was done prior to replacement to make sure on the size needed..

[norcim]

The thing is the fan noise is significantly reduced when the 6" filter is removed. they are telling me the problem is a lack of return air and that I should increase my return air from 1440 to 2000cfm. My supply is 1480cfm. I'm wondering if it is reasonable to assume the extra turns are causing a reduction in air flow equal to or greater than the filter. If so would adding more return air make any difference since the extra turns could be causing a bottleneck. And I am wondering why you would need 2000cfm return with only 1480cfm supply. Do you think this is worth persuing or should I just live with the niose. I still Owe them for half the job.

[Advanced Response]

Please post the whole model #'s of the furnace and a/c?

Also where are you getting the cfm from??? Is this a variable speed model... I don't know rheem very well so I don't know the model numbers very well..

Doc can answer questions better on rheem than I can.. But I still think on that size furnace(120K) it needs either both sides of the furnace used or the bottom to get the correct airflow.. I could be wrong..

Post more pics and measurements of your ductwork with explanations and model #'s and sizes of the furnace and a/c.. We can still help you with more info..

J

By saying the return must come in from the bottom,, I mean that the furnace must be placed on a balance box..

[Edited by Advanced Response on 02-07-2006 at 09:52 PM]

[norcim]

The ac is a 3 ton #ramm-036jaz also rheem. They did a load calc. I had already done my own using software I came up with 2 ton ac and a smaller furnace they said I should trust them. I did.

[Advanced Response]

Take some more pics and post some measurments of the ductwork.. Also if you could post the full model # of the furnace it may help one of the rheem pro's..

Doc or the bald one should be along shortly.. They really know Rheem products..

J