I get constantly confused by the terms return duct and supply duct. What distinguishes them? To me it almost seems like the system is one giant loop so where does one start and the other begin ?

Thanks
Gene

 

Yes it is a big loop. But the supply is off the top of the furnace and called the plenum. This is where the most heat will be comeing off the furnace. On the side of the furnace will be the cold air drop. This gets the return air back down to the blower under the furnace. So it can blow the air back up into the supply.

 

With respects to Ed...simple terms worked best for me in the beginning

If it sucks...it's a return

If it blows...it's a supply

 

Okay, great responses but I am still confused - maybe it's cause my air handler and ducting is unorthodox ???

Ed, you talked about supply plenum being above the heater - this is assuming the fan is blowing up I guess - cause my airflow is down.

My system looks like this in the 1st floor HVAC closet.....


___TOP___ large 30'' x 30" intake opening in square duct
| |
-----------
| | Filter Media drawer
-----------
| |
| | A/C "A" type coil
| |
-----------
| |
| | Electric Heater Strip/Blower
| |
-----------
| BOTTOM | Duct to crawlspace


All the duct/plenum is below in the crawlspace to the other rooms. Does this make any sense ? So everything above the blower is return and below is supply (remember airflow is downward).

Thanks
Gene

 

Yes, you got it right... Your set up is Return duct above, and supply down below..

Your set up is not seen often around here... 99% of the homes here has a basement, and set up is like Ed said.

 

Ahhh, OK now I see. I guess I should have known it's a rare setup when I noticed the air handler was installed upside-down

While we're at it...one more question for the brilliant minds here...

While the blower in my Trane air handler is not variable speed it does have the capability to be wired for 3 fixed fan speeds (L,M,H) and right now is wired to High speed. I was curious if there is some way to get an intelligent controller (like an IAQ) to select the Low speed connector for when the dehumidify function is running. I guess a transformer would be in the picture if this is possible at all. Or is it possible just to swap the blower for a variable speed
model without replacing the entire air handler. Its a Trane TWE024P.

Thanks!

 

Not rare at all . We do many units like that . You call it a counter flow furnace is all.

You could put in a humidity control and a relay to cut the blower back down to heat or lower speed when you are on AC. Most of the time it will be on M for heat and H for AC

BIG BIG cost$$$$$$

Now go to http://aboutsavingheat.com/crawlspace.html

You want 6 mil poly on the ground insulation on the walls. Two small register outlets in the duct work in the crawl space and one small return to that return duct on top of the furnace.

 

So let me see if I got this right....

Condition...................Blower speed (optimal):

A/C.......................... HIGH
Heat/Humidify.............MEDIUM
Dehumidify.................LOW

Is the reason for MED on heating so there will be less draftiness when the blower is on??

Thanks Ed..

 

I wouldn't run the blower on low in dehumidify mode! That's is almost too low, and may risk compressor flooding. Unless you got a TXV on the coil.

Only time low is used in heating if the temp rise is not too high.. and only in fan only mode.

 

OK, it has a TXV but better to be safe and run in MED for dehumidify.

Thanks!