Breaking back of Furnace Fan?

[232gulfstream]

For Rheem residential style furnace there is no such thing as breaking the fans back correct? Fan is located at the bottom so air needs to travel through furnace element then DX coil and then into the duct so it should be fairly laminar flow leaving the DX coil at which point I want to 90 after the supply duct gets into the ceiling area. Normally this would be a major no-no but I don't see anything in the installation manual that won;t allow this to be done.

 

[willard3]

Do you mean braking and not breaking?
If you mean braking, direct connected fan's flow cannot be changed up or down without major control modifications.

 

[berkshire]

A lot of residential furnace/ ahus have provision for selecting fan speed for heating and a different speed for air conditioning This information should be in the service manual. If you put turn vanes in the duct you should be able to turn 90* without too much loss.
B.E.

You are judged not by what you know, but by what you can do.

 

[LittleInch]

Why would it be a "no no"?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[232gulfstream]

 

[berkshire]

Yes that is what I mean, by turn vanes, The control panel for the furnace should have a provision for several speed taps to fine tune the unit for heating and air conditioning.
B.E.

You are judged not by what you know, but by what you can do.

 

[232gulfstream]

So since the supply fan is on the bottom of the unit and the air runs through the furnace and the cooling coil I should have fairly straight flow leaving the unit which wouldn't be bad for a 90 degree mitre with vanes going back over itself which is normally frowned upon.

 

[BronYrAur]

I think i understand now. You are concerned that the rotation of air through the fan is in the opposite direction of the direction that the air will leave the 90 deg elbow, correct? If that elbow were right at the discharge of the fan, it would be a major pressure loss. If the flow can straighten out, then you should be ok. Check out page 4 of the attached

 

[232gulfstream]

Yes BronYrAur! This is exactly what I am talking about. Seeing that the air goes through furnace and cooling coil then about 4-5' of straight duct before the 90 I should be ok. There is nothing in the I&M that prevents you from ducting these whichever way you want. I just know from past experience that configuring the duct work this way is never a good idea.

 

[BronYrAur]

My experience with small contractors is that the installers don't know anything about this. No offense to them. They have hands-on and other technical skills that I don't have, but no one ever teaches them about stuff like this. Loads are done by "square-footing" everything, and past experience is their guide. I doubt any real design work goes into most residential installations, which I am guessing this might be. I'm glad you are looking into it.

 

[232gulfstream]

I'm a design engineer using light commercial furances and I have a situation that would really be a clean layout if I can run the ductwork like this. I know all too well about system effect and have been to many labs where they actual show dP and CFM by applying various elbows to the outlets of fans. I'm thinking in this case I can "cheat" the standards.

 

[BronYrAur]

Stupid question..... can you get a unit with the fan curvature in the other direction?

 

[232gulfstream]

I don't think so. These are pretty much residential style units.