New Furnace installation problem?

[Greg Johnson]

I hired an established 20 year American Standard authorized "Customer Care" Dealer size and install an AUY080 variable speed 2 stage high efficiency natural gas furnace in my house last fall. It replaced a 30+ year furnace. Over the past two months we've had a number of nights that fell to around -8 to -11 F, about as low as it ever gets for this area. During this time, the furnace has never needed the second stage at all. In fact, the only time the second stage goes on is when the 2 stage thermostat is manually increased more than 2 degrees.

There are return ducts in almost every room upstairs. The return air flow is very noisy (to my taste), even in the rooms farthest from the middle of the house, where the furnace is located. The supply ducts are not noisy at all. When the second stage is on, the increased airflow is very loud in my opinion. This wouldn't be a problem for the heating season, but full fan is used for cooling.

I'm ready to give the contractor a call and ask him about this. But I'd like to get more informed first. How much (if ever) should second stage be needed? Is it normal to put up with a constant rumbling of air in return ducts? The opening in the (upflow) furnace side between the side return duct and the furnace is smaller than the blower, leaving me to wonder if this is at least part of the return noise problem. How long should the on cycle times be, for a 30F degree day, for example?

My house is a split level, about 1700 sq ft, 1350 "livable" and is in eastern Massachusetts.

Thanks!

[m Ransley]

Was it noisy before, so the ductwork is the same? How long are your cycle times, longer cycle times put less wear on your equipment,

[Greg Johnson]

To be honest, I don't remember exactly how loud the old furnace sounded. I bought the house early fall last year. Because the heat exchanger was suspect when I had it inspected before the heating season, I didn't give it a chance to run much. But I do know that on 2nd stage/full fan, it definately is louder than the old furnace.

The ductwork is the same. Cycle times vary from 12-35 minutes, depending on outdoor temp. This is with the Braeburn thermostat set to

1 degree differential. (Default was 0.5 degree). .

[TURTLE]

This is Turtle.

Most HVAC contractor will set the btu rating of the heat run time at about 90% at Maxium Temperature outside as you say -8ºF to -11ºF . The reason of the long run time here is you have the two stage gas furnace and first stage will tend to run a long time for the second stage is if it gets in trouble and falls behind.

TURTLE

[~KJPRO~]

Newer furnaces have to move more air to reach a lower Delta T across the heat exchanger. Therefore if the ducting is inadequate, it will be noisy and very displeasing.

~kjpro~

[Bubba]

Of course the second stage should be needed. It all depends though of how or if they did a proper load calculation of your home to determine the proper size furnace needed. At -10 degrees outside you should be seeing the second stage of heat coming on unless the design outdoor temperature in your part of the world is -40 or something? Should ductwork be noisy? No, not if properly sized and installed. This however is very hard to find as many companies just slap it in and run. You have to find someone good, period. On cycle length just depends. Thats just a guess over the internet. Have your contractor back out and go over these things with him. If you arent satisfied, try another contractor. Bubba

[Greg Johnson]

I understand that, both the return ductwork and the warm air duct work are similarily sized, yet the warm air ducts are nearly silent while the return ducts are noisy. I assume that American Standard's dealer sized the system properly for the ducts, is that an unreasonable expectation to make?