blower speed

[John Dirks Jr]

Consider a new 90% gas furnace & AC with 4 speed adjustable blower speed. What would be some common criteria for deciding which speed to set the blower at? This is not a variable speed unit. The blower speed can be set but stays at that speed until manually changed.

Should a person consider a different speed for heating season as opposed to cooling season?

[Marc]

Use the manufacturer's recommendation. That would be low and high for heat and cool respectively with a 3 speed fan. I don't recall installing a system with a 4 speed fan. Must be a northern phenomena.

Marc

[John Dirks Jr]

Use the manufacturer's recommendation. That would be low and high for heat and cool respectively with a 3 speed fan. I don't recall installing a system with a 4 speed fan. Must be a northern phenomena.

Marc

It might be a 3 speed..I could be wrong. I'll check the guide.

[John Dirks Jr]

Trane XB90. Its a 4 speed.

1 heat terminal, 1 cool terminal, two park terminals.

Black = high -currently set to cool

Blue = med high - currently set to heat

Yellow = med low - currently parked

Red = low - currently parked

I will say that the high speed setting in cooling mode is moving twice as much air as the old system. I don't think I need that much airflow. I may bump the cooling down to med high and the heating down to med low. Any concerns with making this adjustment?

[Marc]

I would not make the fan speed contrary to the factory settings without consulting the manual.

There's factors in the functioning of that furnace that are well over an HI's head. Over an HVAC technician's head too.

Marc

[inspector57]

Reducing air flow on cooling can result in ice on the coil and higher utility costs.

"you" may not need the air flow, but the cooling system may.

[rkenney]

Air flow (volume) and velocity (pressure) are two different things. In this case you are changing both because you are varying the blower speed (source) as opposed to modifying the duct-work. (typically done wrongly when the basement is 'finished')

What you ultimately are looking for is a temperature differential between the inlet air and the outlet air (at the air handler) of about 15 degrees for a high efficiency unit and about 18 to 20 degrees for an older unit (SEER less than 10).

Go ahead and reduce the blower speed a step and see what happens. It should be alright, the different speeds are there for different size house installations. (large house needs to move more air a further distance)

Possible annoyances of a high blower speed include air noise and wide temperature variances across a room.

[Les]

John,

I have the exact same unit here at the office. Off the record, I did what you asked. The office that is 40' away has extremes, but the other offices and rooms are more uniform. I have access to duct run dampers that get fiddled with spring and fall. Residence likely will be different.

[John Dirks Jr]

Can blower speed affect cycling frequency of either AC or furnace?

For the record, I have not made any changes yet. My house is not that big so uniform distribution has always been pretty good. The new air handler is moving way more air than the old one. My thoughts are that a slower speed (if adequate for comfort needs) might save a little on the electric bill.

[Les]

John,

I think the cost savings would be quite small, if any. Marc or another electrified guy could do the math. When I was investigating the office situation, I went to Walmart and bought a fog machine for abt $30 and used it to see the air flow patterns. Safe, quick, common sense and learned alot.