Need help with returns - Size & how many

[tjdorrie]

Have a question about returns.

It looks like I may be replacing my AC unit with a carrier Heat Pump (25HNA636A003), coil (CNPHP4221ATA), and furnace(58MVC080-14).
My house is single story 1775 square foot.
I have one return and I have been told that it is under sized for my current and new unit.

The front of the grill is 14X20 but behind the filter the grill opening is only 10X16. The wall cavity is used to get to the furnace/blower in the crawl space, the cavity is 32X10 but the opening to the furnace is only 16.5X8.5

One dealer told me that expanding the floor opening is all that is needed. That opening is currently 16.5X8.5 and to the other side of a floor joist you can add (knock out) another 7X8.5, making the cavity floor 23.5X8.5 and the grill 10X16.

Another dealer told me that the cavity floor of 23.5X8.5 and the grill 10X16 is still not enough and I would need another return. The plan was to add one to the master bedroom. He gave me two options:
1-connect up to the furnace/blower ducting in the crawl space and run it to the bedroom floor.
2-remove the top from the wall cavity and run the return through the attic to the bedroom ceiling. (This was his preferred option)

My question is, do you think I need a second return and which would be the better option 1 or 2.
option 2 interests but confuses me because adding the return ducting to the top of the wall cavity means you still need to pull air from the opening that he felt was too small already(23.5X8.5), and wouldn't all the air enter through the grill not the top of the cavity anyway?

I would prefer to actually put the return on the bedroom ceiling, but I am not sure that option-2 is technically the best option. Please let me know you thoughts.
Thanks for all your help...

[dash]

Add a return. I wouldn't use the wall cavity,likely too small/restrictive,plus it can pull air from the adjacent cavities,and thus the attic or crawl.

[vstech]

code in our area is homes with over 1600Sq feet, or multiple floors require two returns, or a return on each floor.
1200CFM is needed, a 14x20 filter is pretty small. expanding the ductwork to that return is not going to fix your problems. I would add in a new return and filter on the other end of the home.

[tjdorrie]

I plan to expand the duct work & add a second return in the master bedroom, just not sure if I can use the wall cavity or will need a new home run.

The main return will be using the wall cavity 23.5X8.5 for a 14X20 return.
Do you think that the wall cavity is big enough to supply a second return in the bedroom, or will the second return need to come straight from the blower as well?

The main reason I ask is if we run the second return from the top of the wall cavity (attic) I can put the return on the ceiling in the master bedroom. If i run it from the blower (crawl space) it has to be on the bedroom floor.
Thanks.

[dash]

And what is wrong with a floor return??

[tjdorrie]

My preference for a ceiling return vice a floor return was not technical, its just real estate that I can no longer use for furniture. However this does appear to be my best choice.

From reading and talking I understand that more return is normally better, but since my dealers will install but thinks the main might really be enough on its own, can you tell me how many square inches I would need for a 3 ton unit.
My 14X20 grill (280sq in) has to go through a opening at the floor of the wall cavity 23.5X8.5 (199.75sq in). How many more square inches does my system need so it is not starved for return air?

[dash]

Correct minimum size is determined by a Manual D calculation,which takesinto consideration the supply and return ducts,length,type of fittings ,grilles,type filter,elbows,etc,etc..

Experienced guessing is all we doing here.