Is it unsafe/expensive to run central air/heat fan 24/7

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  #1  
Old 06-07-14, 06:17 AM
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Is it unsafe/expensive to run central air/heat fan 24/7

Hey All,

I have a 2 floor (finished basement & 1'st floor) single family with forced hot air/central air. The entire house is a single zone. The basement is always much cooler in the summer while the upstairs gets warmer. As a result, when the AC kicks on, the basement ends up freezing while it has trouble keeping the first floor cool. The last two days I have set the fan to manual to circulate the cold air from the basement throughout the house, even while the AC is off. It has kept the house comfortable and the AC has run much less frequently.

What I am wondering is, first and foremost, is it safe to continuously run the fan or is there a risk of burning the fan out or starting a fire? Second, is it economically smart to run the fan 24/7 or would it be cheaper to just let the AC kick on more frequently? It would make sense to me that the fan would use less electricity, but I am no expert here!

Thanks for any feedback/help!

-Kevin
 
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  #2  
Old 06-07-14, 07:38 AM
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Obviously, running the fan 24/7 will cause more wear to the fan. However, that said, it should be considerably more economical to do that rather than run the A/C compressor. If your basement is like mine, it rarely needs air conditioning, as it's much cooler than the first floor. What you may want to consider is closing (or nearly closing) the dampers in the runs for downstairs, letting almost all the cold air go upstairs where you need it.
 
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Old 06-07-14, 09:28 AM
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We run our fan 24-7, but the Trane unit we have has a high and low speed. Until the heat pump kicks in it runs almost silently. If you have your units serviced at regular intervals, and if the company is responsible, they will lubricate the bearings of the motor and keep it in top shape.
 
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Old 06-07-14, 10:23 AM
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Can not think of any safety reason not to run the fan continually when you need cooling . They are made to run .

Careful about closing off too many registers / grills . If you reduce the air flow too much , you could cause yourself problems . Freezing up the A-Coil , for instance ?

I would think the fan would use less electricity than the condenser unit ?

Plus , if you have humidity problems with the basement , it might help that ?

God bless
Wyr
 
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Old 06-09-14, 04:50 AM
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running the fan all the time can raise RH levels by 10%
 
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Old 06-15-14, 08:54 AM
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@airman - I never thought of that! Any idea what causes that? My inner nerd can't figure out why that would be and it is driving me crazy :-D

@all - It is working pretty well so far. On especially hot days I turn the fan to manual on and allow it to circulate the cold air from the basement. So far, I haven't yet had to turn on the AC, which my electricity bill is very happy about. Thank you all for the information!
 
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Old 06-15-14, 10:34 AM
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Average size coil and drain pan can have 6 - 8 lbs of water on then. Running the fan just 're evaporates the water. Large units and higher seer make this worse
 
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Old 06-15-14, 10:38 AM
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It's better to balance the system and seal duct leaks than to run the fan continuously -> continuous fan uses 300-500watts and reevaporates moisture off the coil when the condenser shuts off.
 
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Old 06-15-14, 11:05 AM
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Originally Posted by sr71000
when the AC kicks on,
the basement ends up freezing while it has trouble keeping the first floor cool.
...
I have set the fan to manual to circulate the cold air from the basement throughout the house, even while the AC is off. It has kept the house comfortable and the AC has run much less frequently.
Using a fan to move already cool air where you want it
is MUCH more energy efficient than taking hot air and making it cool.

You should be able to get a good idea of the cost/benefit between fan vs ac from simply
comparing the amps/wattage ratings on the a/c unit versus the furnace's blower fan.
I expect you will find that the fan is generally going to use MUCH less power than an a/c unit.

I've got a somewhat similar system, forced hot air, but without central air
(old stone farmhouse with window a/c units).

I found a basic programmable thermostat- (fan/ auto)-(heat/cool/off)-(sleep, wake, day, return)
can keep the house quite comfortable, without ANY A/C at all. (so far)

I just pulled the 20 x 24 fan access panel, put in a 20 x 24 air filter.
Then leave the thermostat set to trigger "cool" if it gets above 74 degrees during the daytime.

Basically, if it warms up upstairs, the thermostat kicks in, and the fan to circulates cool air from through to the upstairs until it's comfortable. Once the upstairs has cooled off, the fan shuts off.

You might be able to replicate this by simply setting the thermostat to "cool, fan auto" and
flipping the breaker that provides power to the a/c unit.

- I'm curious, (for the experts)
is there any sort of logic controller available which could be added to this sort of setup,
something analogous to a furnace pre-heater delay,
so that when the cooling circuit kicks in, it runs the fan for 1/2 hour without triggering the a/c compressor, then if circulating the air doesn't bring the temp down enough, it allows the a/c compressor to start up?

Hal
 
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Old 06-15-14, 02:17 PM
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The Honeywell VisionPro 8000 series thermostat has a circulate feature that will cycle the fan even when a cooling demand is not present. It is better than running the fan continuously.

Hal : A 2 stage thermostat will accomplish what you posted of. Connect the condenser to the Y2 terminal.
 
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Old 06-16-14, 09:37 AM
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You have to be really careful pulling return air from the basement if there's a natural draft water heater down there.
 
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Old 06-16-14, 09:55 AM
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Originally Posted by Houston204

Hal : A 2 stage thermostat will accomplish what you posted of. Connect the condenser to the Y2 terminal.
Thanks, that should be quite helpful.

Follow up question- Any in-duct dampers that are activated by DIFFERENCES in temperature?

Idea is - a cool outside air intake, with a duct-damper that opens if the outside temperature is lower than the inside temperature.
 
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Old 06-16-14, 10:41 AM
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Originally Posted by Muggle

You have to be really careful pulling return air from the basement if there's a natural draft water heater down there.
Yes, good point! Pulling cool air from a basement is NOT a good idea if you have gas appliances, or if you have an airtight modern home.


I'm in an old house that also has a "passive cool air return" e.g. big hole in the first floor with a grate over it. So, when I open the furnace access panel to create a basement return, I'm careful not to create a negative pressure that sucks CO2 or CO back down the chimney.

That does lead to a another constructive question.
Does the OP's basement have windows?
I've had good results pulling in the cool night air using the furnace as a fan with a basement window open. Now, I'm pulling the furnace access panel to make a big return, but I'm quite impressed with how quickly it works.

Oh, and getting back on track - cost?
Now, you'll have to check the rating of your central air unit (likely in watts)
to your fan motor (like rated in horsepower, 1 hp is ~750 watts)

Averages, central a/c unit is ~3,250 watts, average fan motor is 1/2 hp or ~325 watts.
So, 24 hours running the fan should be about the same as running the central air for 2.4 hours.

So, if you can setup the fan to turn off once the temperature is comfortable, even better.
 

Last edited by Hal_S; 06-16-14 at 10:58 AM.
  #14  
Old 07-22-14, 09:31 PM
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I also have a 1 story with a finished basement, and also have the same issue as you. We find that running the central AC fan does circulate the coolness fairly well but use a couple of box fans to help. We do not have a return down stairs, so running the fan results in a draft of cool air coming up the steps. We use a fan to move that cool air around the kitchen and living room.

We live in Montana so we use the time honored tradition of opening everything up at night to get the cool air into the house, and then closing everything before going to work/school. When I get home it will easily still be 72 on the main floor. Once we start adding heat loads, the temp will go up, and thats when we run our fans.

We were coached to keep all the registers all the time to enable thorough air exchange, and to keep the air moving in the basement to prevent any moisture build up down there. In our environment, we don't need to worry about humidity, but there are appliances and a sump well down there.

With the fan(s) running at peak heat times, our summer electricity bill averages $53. I just hate the idea of the AC consuming all that power when there are passive things we can do. I am going to look into a solar power attic fan next to see if that drops our energy bill.
 
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Old 08-08-14, 10:39 AM
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And another follow up-

Just noticed that the OP is in Massachusetts... AC? Really? (grin)

Anyway, you should have cool nights, unless your in a major urban area (basically Boston?)

I've had REALLY good results cooling the house this year by simply running fans at night.
There's an exhaust fan in the attic window, and there's an input fan on the first floor.

With daytime temps are in the 80-90s, and evening temps in the 60s, pulling cool outside air in
generally cools the house down to the 60s by early morning.

If you get the house cooled down by morning, then circulating air with the furnace fan during the afternoon and evening keeps it comfortable.

Much cheaper to run a few fans for 10 hours than a large air conditioner for 10 hours.

And BTW, circulating the cool air with the furnace fan has kept the
"it's too hot, I want the AC on" family member (there's always one) satisfied..
 
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Old 08-09-14, 09:00 AM
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IMO if you have a two story home with a single HVAC system you would need to operate the fan 24/7 whenever you are in air conditioning season.
Warm air rises and it is the only way you stand a chance of equalizing the temperature between the two floors.
Heating is the reverse and it may not be necessary to operate the fan in heating season.
It seems lately, in our area anyway, that new two story homes are being built with a system for each of the floors.

Commercially, having fans start/stop when heating or cooling is generally unheard of.
The costs and wear to do this are insignificant.
 
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Old 08-09-14, 09:13 AM
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Originally Posted by GregH
It seems lately, in our area anyway, that new two story homes are being built with a system for each of the floors.
Curious - where in Canada?
I ask because when I've visited the British Columbia area, I was sort of surprised that
for new construction outside Vancouver itself, some places didn't have A/C...
 
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Old 08-09-14, 11:31 AM
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Right.....
I live in Central Northern Canada in a cold climate where central forced air heating/ac is the norm.
Southern British Columbia has a very moderate climate being on the Pacific Ocean and does not surprise me you didn't see much a/c..

Where I live we have extreme temperature swings.
At one time we used Fahrenheit and in the winter temperatures above 0 deg F were seen as fairly warm, below 0 was fairly cold and -30F was considered very cold.

Today here is a bit cooler but yesterday was about 85 deg F.
 
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