Model# of furnace and a/c?

 

If you're talking about an air conditioning system for cooling, keep in mind that the air conditioning requires X amount of air flow when cooling the home (the outdoor unit is running).

 

We do tons of Rheem (Ruud) and I'm not aware of any of their units that allow a blower speed change at the thermostat. Even the manufacturers that do (Carrier Infinity comes to mind) only allow this change for the "Fan On" mode for quiet circulation between cycles. When the AC comes on it requires a certain amount of airflow and must run at that speed to operate properly.

Try adding some acoustic insulation to your return duct, or even possibly have the duct relocated to reduce the noise.

 

Tell us about the temp/%RH you getting from the a/c. It may be advantageous to slow the blower to lower %RH in your home. Amazon has temp/%RH meters for minimal $.
Regards TB

 

Is this a mobile home? Those are the ones I know that have a furnace closet near the front door.

 

Not a mobile home. House has vaulted ceilings and very limited attic space. In between floors there is barely enough room for ductwork. Had to cut the floor open upstairs when we replaced ductwork. So what I have is a very large 2x 16x22 grills for my main return and they are directly below the main ac closet. These are the only returns in the whole house. There is no rattling or whistle just a very loud woosh wind noise. I have to double the TV volume to compensate ambient noise must be close to 45db. Can we slow the fan down? The bottom of the ac closet is open on two sides and the other two sides have closets. Would have to do some kind of fur down inside a closet to run a return upstairs....

 

I got the instruction manual that came with the Unit and took it apart today, it has several wires coming from the motor. RED BLUE BLK, 2 BROWN and a WHITE. According to the book the 2 brown goto a capacitor and the white a nutral, and the blue/blk/red are speed control. The default installation had the RED (SLOW) to HEAT, BLUE (MEDIUM) to COOL, and Black to "M1" which it said to connect any unused motor taps here.

This is for a RUUD/RHEEM system, with control board "1097-200", if that means anything to anybody.

I switched the HEAT and COOL, so now the cooling is on slow speed, and the furnace is on medium. left the black (HI) on M1. It does seem to have made the system a bit quieter for cooling. Still noisy though. I wonder if I should line the though wall "box" with Plenum??

How will lowering the blower speed effect cooling performance? How will raising the blower speed effect Heating performance? is Low blower speed even safe on the Heat? I assume so as the installer had it setup this way.

 

so, I have a 3.5 TON unit, and the specs for the blower are

LOW- 1250 CFM
MED-1555 CFM
HIGH-1810 CFM

so i think im ok on low speed as 1250/3.5 = 357 CFM Per TON. A little on the low side, but hey, it's quite humid here in San Antonio, so probably for the better. should be no risk of freezing coils or anything.

 

Blower speeds are chosen for a reason - system performance. You can screw up your system or fry the blower motor by connecting the wrong wires. Those specs are based on static pressure. The airflow may be less than you think.
You'd be better off building a return trunk (ductboard will help reduce the sound transmission) to put some distance between the blower and the inlet.

 

You need at least 1600 CFM to safely run your system in cooling. Where you have it now you may not be freezing the coil, but you could be risking compressor damage.

Best thing you can do to reduce return air noise from a furnace on a platform is to line the entire return chase with duct board, sealing all seams with mastic. Return chases below a platform are often open to wall cavities or bathtubs, which can act like echo chambers.

 

1600 cfm would be 457 cfm per ton... What is the reasoning behind this being the minimum level for safety?

It is quite humid here in south Texas I already noticed the supply air feels much cooler and drier from lowering to 1250 cfm/357 per ton from 1555/444 cfm.

I mean no disrespect just curious I'm only a home owner

 

I miscalculated. 3.5 x 400 = 1400 CFM. So if you are actually moving 1250 CFM then you are at 357 CFM/ton, which is a good setup for dehumidifying.

Your OP was a noise complaint. Slowing the blower speed reduced the noise but I take it you would still like it to be more silent. And if so I still recommend lining the return cavity with duct board and sealing it with mastic.

 

If it has a TXV, you can safely run down to 320 CFM per ton.

 

If your "return box" has a large amount of hard surface area some sound deadening material may help.

 

amazing no one said anything about next winter when the heat comes on at medium speed that the heat noise will then be louder if nothing was done about lining the inside of what duct he has for the return.

dogboy

 

Yeah its still louder then I'd like. That's a good idea about lining it. Might be hard though as the only access to the return box is the two 16x 22 grills. The inside of the box is bare concrete, dry wall, and plywood and there are vivible gaps between tthelywood and concrete and the drywall is exposed to the studs.

 

Your return air box is much more generously sized than mine, as far as height goes (10"!! if that!!) and I managed to get it both lined and sealed. The lining and sealing accomplished two things: (a) no longer drawing air into house from attic through stud cavities, and (b) pleasant blower noise reduction

Duct board is the best candidate for this task. Even with the shiny side out it will give you acoustic qualities you want. The open stud bays you mentioned in your reply are echo chambers, as is the bare concrete floor. Line all of it and you will notice a pleasant drop in noise, and you may also notice improvement in your HVAC performance, as you are no longer sucking on building cavities as part of your return air path.