HVAC question - manual fan setting

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Apr 13, 2017
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Does anyone run their HVAC fan all the time, versus using the auto setting?

It's been really hot in the east. We had a Carrier dual speed system installed a few years back. Our house is older (70's), with not the best insulation (that is my next improvement.) The temp between the upper and lower floors seems more balanced when the fan runs all the time. It runs really slow (almost imperceptible), but then ramps up when it calls for cooling.

The temp spread is most obvious at night, when the system doesn't run as often, and the humidity rises somewhat. (By my feel anyway).

Should I look at a remote temp probe for upstairs? (I'm not sure if that exists).

Thanks.
 
We have our HVAC fan set to run continuously. As you have noted, keeps the temps more even throughout the house.

In the evening in summer, usually have to set the temp a degree or two cooler since there isn't much heat load at night. No sun, no cooking, no TV on so not generating much heat and the AC won't come on to dehumidify the air.

Also have a separate dehumidifier in the basement that is set to 55% humidity.
 
This will be a debate just like thick vs thin oil. Do NOT expect to get a consensus. 🤣

We're seeing the same unusually high temperatures and our Ecobee thermostat normally lets the temperature go up to 75º during the day, then 72º by the time I get home (my wife works 7a7p so she's home later). If I allow that, too often it can't recover and get down to 72-73º, so we've been keeping it ~73º most of the time. We've had thunderstorms a couple days that drop the outside temperature 15-20º and that has definitely helped. Otherwise, the blinds and curtains are closed during the day or at least the ones facing the sun so it's not dreary dark inside.
 
We just had a new system put in and it has a fan that is always running. It's very quiet and only uses like 50W-60W. It makes a difference in heating and cooling distribution. I used to have a large floor fan blowing up the staircase to keep the upstairs cool. No longer needed.
 
Has its benefits for balancing temps ! but in summer raises humidity a bit. And in winter feels like a cool draft and depending on vent placement can make your home feel cool and know one likes a cold breeze blowing over them on a cold winter day.
 
Depends on your ductwork. In the summer your attic ducting will be very hot, so if your in cooling mode then you don't want to do that - will add more AC load because that air ultimately will need to be re-cooled. Winter would be the same - more heat load needed.

If your ducts are in the floor just above the basement it might be opposite - running constant fan might cool the air in addition to redistribute it.

It also depends on where your inlets and ducts are. For example if your outlets are in the floor, and inlet in the ceiling, in the winter you could run constant fan to pull the hot air from the ceiling and redistribute it at the floor.

There is no right answer because every house is different.
 
Every 2 story is warmer on the second floor in the summer unless you have zoned HVAC. imo the easiest and lowest cost solution is a cheap window AC for the hottest months. $139 basic unit really helps get you a good night's sleep.
 
Every 2 story is warmer on the second floor in the summer unless you have zoned HVAC. imo the easiest and lowest cost solution is a cheap window AC for the hottest months. $139 basic unit really helps get you a good night's sleep.

The previous owner of our house told me the upstairs gets to 80*+ with ac on full blast during the hottest days of the summer. It's the original 20yr old AC system, looks fine and does a great job cooling the bottom floor and heating the entire house. I don't think the original architect did a good job with the AC duct design / balancing the upstairs with the 1st floor. There are plenty of registers and intakes just not much flow, and yes I have checked the ducts to see if they are open.

We ended up going with mini splits for the upstairs rooms since it was not possible to use window units as the construction of the home did not allow for a convenient location to cut a hole in the wall for a window unit.
 
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This will be a debate just like thick vs thin oil. Do NOT expect to get a consensus. 🤣
This, in a nutshell.^

I run the fan continuously in the winter to keep the air moving. When I had my latest HVAC system installed, I opted for an electronic air cleaner and a UV sanitizing light in the ductwork. This helps filter/clean the air.

In the summer I have the fan only run when the AC is running as I've been told that running the fan continuously in the summer doesn't allow the coils to dry and this basically pushes humidity back into the house.

YMMV, of course.
 
In the summer time , place your fan setting in AUTO. If you run your fan all the time during a/c operation, the moisture that is still on the evap. coils after the a/c turns off, will get recirculated in your house and will increase your inside humidity levels by quite a bit. . The only only time you want to run your fan all the time is during the heating season if you want.
 
One minor adjustment that can supposedly help is moving the intake register from the floor up to the ceiling. If you are find with drywall and sheet metal work, it might worthwhile.

This allows the room to fill with heavier cold air before being recycled. That's what the HVAC estimator told me when faced with the warm upstairs cold downstairs problem.
 
Every 2 story is warmer on the second floor in the summer unless you have zoned HVAC

The previous owner of our house told me the upstairs gets to 80*+ with ac on full blast during the hottest days of the summer.
Mine is zoned - up / down.

In summer downstairs almost never turns on, and upstairs runs constant when its super hot. I imagine it was put in by the builder to slightly undersize the system - because no builder would spend an extra cent for anything other. It keeps up but barely. I put in sun blocking bug screens on the south facing windows - I think as small as that area was it did help some.
 
We have our HVAC fan set to run continuously. As you have noted, keeps the temps more even throughout the house.

In the evening in summer, usually have to set the temp a degree or two cooler since there isn't much heat load at night. No sun, no cooking, no TV on so not generating much heat and the AC won't come on to dehumidify the air.

Also have a separate dehumidifier in the basement that is set to 55% humidity.
this is what I have been doing - I'm not sure why I didn't think of it before. how big of a humidifier are you running, and do you need to replace them often?


This will be a debate just like thick vs thin oil. Do NOT expect to get a consensus. 🤣

We're seeing the same unusually high temperatures and our Ecobee thermostat normally lets the temperature go up to 75º during the day, then 72º by the time I get home (my wife works 7a7p so she's home later). If I allow that, too often it can't recover and get down to 72-73º, so we've been keeping it ~73º most of the time. We've had thunderstorms a couple days that drop the outside temperature 15-20º and that has definitely helped. Otherwise, the blinds and curtains are closed during the day or at least the ones facing the sun so it's not dreary dark inside.
Oh no, not that.
 
The previous owner of our house told me the upstairs gets to 80*+ with ac on full blast during the hottest days of the summer. It's the original 20yr old AC system, looks fine and does a great job cooling the bottom floor and heating the entire house. I don't think the original architect did a good job with the AC duct design / balancing the upstairs with the 1st floor. There are plenty of registers and intakes just not much flow, and yes I have checked the ducts to see if they are open.

We ended up going with mini splits for the upstairs rooms since it was not possible to use window units as the construction of the home did not allow for a convenient location to cut a hole in the wall for a window unit.
HVAC seems to be an after thought to homebuilders. They put in the cheapest system that meets code. Here in WV I have a HP which is worthless <32 degrees. I wanted to be warm so I installed an outdoor wood boiler. 72 feels much warmer with the boiler than 72 with the HP.
I do run the fan all the time in this hot weather for all the reasons stated above. Less power draw when the compressor cuts on.
 
Mine is zoned - up / down.

In summer downstairs almost never turns on, and upstairs runs constant when its super hot. I imagine it was put in by the builder to slightly undersize the system - because no builder would spend an extra cent for anything other. It keeps up but barely. I put in sun blocking bug screens on the south facing windows - I think as small as that area was it did help some.
Be sure and run both systems in dual zoned. My father learned the hard way. He turned the upper zone off because he didn't go up there much. His lower main unit went out very prematurely. Repair guy told him he needed to run both systems so that wouldn't happen.
 
this is what I have been doing - I'm not sure why I didn't think of it before. how big of a humidifier are you running, and do you need to replace them often?



Oh no, not that.

Have a Danby 50 pint unit. I have it sitting next to a floor drain in the basement with a short piece of hose draining it continually into the floor drain.

They usually last about 10-15 years. Most of them have a dust filter that needs to be rinsed off periodically.
 
Be sure and run both systems in dual zoned. My father learned the hard way. He turned the upper zone off because he didn't go up there much. His lower main unit went out very prematurely. Repair guy told him he needed to run both systems so that wouldn't happen.
Single air handler. 2 ducted zones controlled by a separate Honeywell zone controller with a master damper.

My old house had 2 units. Much preferred it.
 
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3 levels, all zoned, so 3 units. 1st and 2nd floors are 3.5 ton Lennoxs, 3rd floor (900sq.ft.) is a 2.5 ton Lennox. All running with fan on auto, but each floor is within 3F degrees of each other. Programable stats that run temps down a couple degrees at night like @Hall does to avoid massive heat loading from oppressive heat and humidity we have been experiencing lately. All units run about the same time/cycles, but obviously longer in higher outside temps. One thing to remember in these situations is to make sure the condensate line is clear. Had first floor line clog last year and it spilled condensate water into the pan underneath the unit and ran it out the overflow drain. I now have automatic enzyme dispensers on all lines and they are clear. They run like a faucet was left on in this weather though.
 
Does anyone run their HVAC fan all the time, versus using the auto setting?

It's been really hot in the east. We had a Carrier dual speed system installed a few years back. Our house is older (70's), with not the best insulation (that is my next improvement.) The temp between the upper and lower floors seems more balanced when the fan runs all the time. It runs really slow (almost imperceptible), but then ramps up when it calls for cooling.

The temp spread is most obvious at night, when the system doesn't run as often, and the humidity rises somewhat. (By my feel anyway).

Should I look at a remote temp probe for upstairs? (I'm not sure if that exists).

Thanks.

You are correct that humidity increases when the fan is always on during cooling. Here is some data to prove it: https://www.americanheat.com/reason-to-not-run-your-ac-fan-during-summer/

1751072301038.webp


But if it feels more comfortable to you with the fan always on and humidity is within reasonable levels, then go for it. I leave mine on at a very low speed during the shoulder seasons when there is no heating or cooling
 
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