More CFM for cooling vs. heating?

[borisf]

We're doing a major remodel of our basement and had to rework much of the ducting of our heating system. We have a Bryant 95 furnace. During this time, we also added a Lennox XC16 A/C system.

Now that things are up and running, our returns are pulling through substantially more air when cooling vs. heating and we can hear that especially in Stage 2 of both, respectively.

Our HVAC contractor is saying that's intentional as it takes more CFM to cool vs. heat. This seems counterintuitive as in Stage 2 heating I'd expect the fan to be running at full speed also. Are they right that I should expect the system to be louder when cooling?

Thanks!

 

[Jadnashua]

It's not uncommon to have the fan run faster during cooling. Think of it this way...how do you feel outside when it is windy? If it's hot out, on a windy day, you're more comfortable because the higher wind speed aids in evaporative and radiational cooling. But, if it's cold out, the wind does the same thing, cooling you off more which is not what you want when you crave heating verses cooling.

Within certain parameters, the amount of cooling you have and the CFM are closely related...it must be between some min/max otherwise things don't work right.

Ideally, you'd have a variable speed fan which can adjust. Initially, running the fan slower across the cooling coils means better dehumidification, but speeding it up, if required, to cool things off to your set point.

In the winter with heating, a really high fan speed means two things: the outlet air will be cooler since it won't be in contact with the heat exchanger as long; and, that faster moving, cooler air is just plain uncomfortable...even though the actual room temp might be 'normal', you can feel cold because of the breeze. It's all a fine balancing act. Noisy ducts is often a sign of poor design.

 

[Sponsor]

 

[borisf]

Makes sense! Thanks.

 

[WorthFlorida]

Your Lennox is rated up to SEER 17.2 A lot of engineering went into it to get to that efficiency rating and still have a comfort. Why it reads "up to" is partly do other factors. Different air handlers impacts SEER rating and duct sizing plays an important part. All smart AC system adjust fan speeds (inside blower and outside condenser fan) as needed by inside and outside temperature and humidity. Depending on the smarts of the system, if the thermostat can read the condenser and compressor size via model numbers it will do further fine tuning of fan speeds and the proper cooing stage for the max efficiency. You have a nice system.