Author Topic: A/C system fan-only = crazy electric bills!  (Read 8789 times)

dcheesi

  • Pencil Stache
  • ****
  • Posts: 553
A/C system fan-only = crazy electric bills!
« on: May 20, 2013, 04:26:50 PM »
tl;dr: Turning the Fan to On (vs. Auto) on my central A/C control panel causes high energy usage, most likely due to the backup heating elements being turned on. Any ideas as to why this might happen? Bad-wiring, flaky circuit-board, etc?

Full story:
For the last two years, in/around the month of May, I've been stuck with insanely high electric bills. The first time, I complained to utility, shut off my outside circuit, etc., but never found a cause. Given that May is the time when I least need heat or A/C, this never really made sense to me.

This time I decided to experiment, based on the one thing I could think of that I was doing differently: since I wasn't running heat or A/C (actually leaving the A/C on 80+ just in case of a heat wave), I would instead turn the fan on full-time to keep air circulating between floors. Low and behold, that was the culprit! Usage went through the roof, and dropped back to almost nothing when I left it off for a day.

Just to be sure, I turned the A/C completely off and left the fan on overnight. I had the windows open, but it never really got cool in the house. And when I went into the bathroom, it was like a sauna! And of course the energy usage was through the roof again.

The only thing I can conclude is that the auxiliary heating elements are turning on whenever I set the fan to On instead of Auto. I didn't notice it before because I always left the A/C on at 80, so the temp. never got beyond that, and I opened the windows at night.

I'm not sure how long it might have been like this, for a couple of reasons:
1) My electric meter was replaced about two years ago, and the old analog one might not have properly recorded the full magnitude of my usage (or the new one could be exaggerating it)
2) The big capacitor on my heat pump blew maybe three years ago, which could have damaged the rest of the system somehow.

I'll probably wind up calling the A/C guy, but I'd love to know what the heck it could be, especially if it's something like a simple wiring problem I could fix myself.

Spork

  • Walrus Stache
  • *******
  • Posts: 5759
    • Spork In The Eye
Re: A/C system fan-only = crazy electric bills!
« Reply #1 on: May 21, 2013, 07:57:30 AM »

My wild ass guess is that it's simply wired wrong.  Most (NOT ALL) of these are going to be low voltage wires.  It's worth pulling off the thermostat and taking a peek.  If that side is right, check the other end.

I run my fan only all the time in the winter to circulate heat from the wood stove.  It shouldn't be doing that.  Mine, however, is still significant when the fan runs: 365 watts to turn that thing.
Some will sell their dreams for small desires
Or lose the race to rats
Get caught in ticking traps
And start to dream of somewhere
To relax their restless flight

amicableskeptic

  • 5 O'Clock Shadow
  • *
  • Posts: 56
Re: A/C system fan-only = crazy electric bills!
« Reply #2 on: May 21, 2013, 08:18:47 AM »
I'd say just stop using your system to circulate air through your whole house.  If you're not running A/C you would probably be better off just having a fan in the room your in blowing right on you.  The feeling of air right on your skin is far more cooling than the small drop in temperature you're getting by circulating air throughout your house with far less electricity used to blow the air.  If you really do want whole house circulation maybe install a few ceiling fans.  They can add value and appeal to your house and will run with pretty low electric usage.  Put one at the top of the stairs to help the multi-floor flow.

Another trick is to use water.  If your bathroom is hot and you run a cold shower in it the evaporative cooling will cool it down super quick.  You can also put a tub of cold water in front of a room specific fan and the water will evaporate and cool things even more.  This solution depends on you being in a semi-dry climate.  If you are in a humid swampy area it won't work as well and could cause moisture problems in your home so be careful.

Nate R

  • Bristles
  • ***
  • Posts: 373
  • Age: 32
  • Location: Milwaukee, WI (Bay View)
Re: A/C system fan-only = crazy electric bills!
« Reply #3 on: May 21, 2013, 08:43:08 AM »
How much is a lot? If it's like Spork's (And many are), you're talking 9KWH/Day if you run the fan all the time.

Spork

  • Walrus Stache
  • *******
  • Posts: 5759
    • Spork In The Eye
Re: A/C system fan-only = crazy electric bills!
« Reply #4 on: May 21, 2013, 08:56:11 AM »
How much is a lot? If it's like Spork's (And many are), you're talking 9KWH/Day if you run the fan all the time.

Yeah -- those are pretty darn big fans and move a whole lot of cubic feet of air.  I was more concerned with the "blowing hot air" part of the description.

9KWh is significant... but if it helps, it's much cheaper than running AC.  (But probably more expensive than a ceiling fan.)  In my case, I've got one HOT room in the winter that I want to push out to the rest of the house.  (Lesson: put your wood stove in the center of the house!  Put a large air return close to the stove!)
Some will sell their dreams for small desires
Or lose the race to rats
Get caught in ticking traps
And start to dream of somewhere
To relax their restless flight

Nate R

  • Bristles
  • ***
  • Posts: 373
  • Age: 32
  • Location: Milwaukee, WI (Bay View)
Re: A/C system fan-only = crazy electric bills!
« Reply #5 on: May 21, 2013, 09:04:34 AM »
How much is a lot? If it's like Spork's (And many are), you're talking 9KWH/Day if you run the fan all the time.

Yeah -- those are pretty darn big fans and move a whole lot of cubic feet of air.  I was more concerned with the "blowing hot air" part of the description.

9KWh is significant... but if it helps, it's much cheaper than running AC.  (But probably more expensive than a ceiling fan.)  In my case, I've got one HOT room in the winter that I want to push out to the rest of the house.  (Lesson: put your wood stove in the center of the house!  Put a large air return close to the stove!)

Certainly more expensive than a ceiling fan. But there may be other alternatives to whole house A/C or furnace fan. In fact, a one room (5-6K BTU) window A/C wil use about 460 watts when the compressor is on, IIRC. For 9KWH, I could run one of those 19 hours/day and still be cheaper than the furnace fan all day.

Of course if you get a variable drive motored furnace, that's a whole different story.

dcheesi

  • Pencil Stache
  • ****
  • Posts: 553
Re: A/C system fan-only = crazy electric bills!
« Reply #6 on: May 21, 2013, 09:12:52 AM »
How much is a lot? If it's like Spork's (And many are), you're talking 9KWH/Day if you run the fan all the time.
A lot more than that; 5000 KWH in one month! That's why I thought it was a mistake the first time.

And it's another reason to suspect electrical heating, as that's the only thing in the system I'm aware of that could push usage to those kinds of levels. Both my normal heat and A/C run about a quarter of that, tops. And if it was a short in the fan or something, my house would probably have burned down by now...

As for why I was running the central fan in the first place, it was mostly to pull up air from my basement. It stays significantly cooler than the upstairs during the day, so I thought it would help postpone the need for A/C as the temperatures warmed up.

Spork

  • Walrus Stache
  • *******
  • Posts: 5759
    • Spork In The Eye
Re: A/C system fan-only = crazy electric bills!
« Reply #7 on: May 21, 2013, 09:19:37 AM »
Does your thermostat have some sort of indicator light for the aux heat coil?  It sounded like you had a heat pump... and the one house I had with a heat pump at least had some indication that the aux coil was on.
Some will sell their dreams for small desires
Or lose the race to rats
Get caught in ticking traps
And start to dream of somewhere
To relax their restless flight

Nate R

  • Bristles
  • ***
  • Posts: 373
  • Age: 32
  • Location: Milwaukee, WI (Bay View)
Re: A/C system fan-only = crazy electric bills!
« Reply #8 on: May 21, 2013, 11:13:13 AM »
How much is a lot? If it's like Spork's (And many are), you're talking 9KWH/Day if you run the fan all the time.
A lot more than that; 5000 KWH in one month! That's why I thought it was a mistake the first time.

And it's another reason to suspect electrical heating, as that's the only thing in the system I'm aware of that could push usage to those kinds of levels. Both my normal heat and A/C run about a quarter of that, tops. And if it was a short in the fan or something, my house would probably have burned down by now...

As for why I was running the central fan in the first place, it was mostly to pull up air from my basement. It stays significantly cooler than the upstairs during the day, so I thought it would help postpone the need for A/C as the temperatures warmed up.

OK, probably definitely the coils coming on.


Does it actually pull air up from the basement? (Are there cold air returns in the basement?) It's possible it's just circulating air from within the living space if the return ducts are only upstairs.

dcheesi

  • Pencil Stache
  • ****
  • Posts: 553
Re: A/C system fan-only = crazy electric bills!
« Reply #9 on: May 21, 2013, 11:45:50 AM »
Spork, the Aux Heat light is not on, but I'm not sure if that light is actually responding to the state of the system or just the state of the thermostat? If the crossed wire was past the point where the legitimate Aux Heat control circuit resides in the system, then the control light might not activate.

Nate R, the return is in the basement. It's actually a finished basement, but I haven't been using it as much and I wanted that cool air upstairs.


Spork

  • Walrus Stache
  • *******
  • Posts: 5759
    • Spork In The Eye
Re: A/C system fan-only = crazy electric bills!
« Reply #10 on: May 21, 2013, 02:46:17 PM »
Spork, the Aux Heat light is not on, but I'm not sure if that light is actually responding to the state of the system or just the state of the thermostat? If the crossed wire was past the point where the legitimate Aux Heat control circuit resides in the system, then the control light might not activate.

That's what I was thinking too.  On mine (warning: it's been a while) there was some magic temperature difference that would kick the aux on...   In other words, if the room temp was 60 and you set the thermostat at 65 -- no aux heat.  If you set it at 70+, you'd get aux heat.

You might try setting the heat to "room temp +15" (or similar) and see if it does come on.  If not... I'm guessing you're wired wrong.

There is a google-able standard for wire color -- though no telling if they used the right wire or hooked it up right on the far end.
Some will sell their dreams for small desires
Or lose the race to rats
Get caught in ticking traps
And start to dream of somewhere
To relax their restless flight

amicableskeptic

  • 5 O'Clock Shadow
  • *
  • Posts: 56
Re: A/C system fan-only = crazy electric bills!
« Reply #11 on: May 22, 2013, 11:10:24 AM »
Finished basement?  Sounds like a super simple solution no cost solution is available, stay in the basement in the summer :)

dcheesi

  • Pencil Stache
  • ****
  • Posts: 553
Re: A/C system fan-only = crazy electric bills!
« Reply #12 on: May 22, 2013, 03:04:28 PM »
Finished basement?  Sounds like a super simple solution no cost solution is available, stay in the basement in the summer :)
Yeah, I need to clean it out again so I can stand to stay down there.  (I actually left it a mess somewhat deliberately, so I would stay upstairs this winter. All logic suggests that the upstairs is better during the winter, yet that's exactly when I find myself gravitating towards the basement...).

reverend

  • Stubble
  • **
  • Posts: 157
    • RobDiesel
Re: A/C system fan-only = crazy electric bills!
« Reply #13 on: June 07, 2013, 12:05:47 PM »
If your heating ducts run through the attic, they can heat up quite a bit, then you push air through them and into the house.

Like others have said, the A/C fan might not always be the best bet to circulate air. Ceiling fans may be better.   It sounds like something else DOES turn on when you turn on the fan, but the easy way to tell is to go and look at your power meter when the fan is off.
Turn the fan on then go look again. If it's significantly faster, you'll know the fan circuit is the culprit.

If I remember right, they run on 240 volts, but it could also be 110 - either way a 10 to 15 amp draw wouldn't be out of the ordinary.


FlorenceMcGillicutty

  • Stubble
  • **
  • Posts: 116
Re: A/C system fan-only = crazy electric bills!
« Reply #14 on: June 07, 2013, 09:54:33 PM »
Doesn't a fan use about the same amount of energy as the A/C? My Dad is an engineer who studied energy efficiency and turning on the fan system was a crime growing up. It will never turn off because it's not on auto. That means the system runs constantly. We always just turned the A/C up to 80 when we needed to use it less.

woodgeek

  • 5 O'Clock Shadow
  • *
  • Posts: 4
Re: A/C system fan-only = crazy electric bills!
« Reply #15 on: June 08, 2013, 06:34:47 AM »
1. The aux coils are prob on their own breaker.  Try just flipping them to 'off' during the summer, if you don't want to get your system wiring fixed.

2. Fan 'on' varies by system.  In many/most newer systems, if the fan is energized without the HP or AC, then it runs at low speed, with dramatically lower energy use.  My blower uses ~400W when the heat or AC is on, but more like 50W in 'fan on' mode otherwise.  To figure it out, put fan on, and see with your hand in the vent if the airflow is comparable to that with the AC runnging, is it as loud?  If so, figure 400W.  If it is moving a little air and very quiet....then don't worry about it.

3. Running 'fan on' during AC weather in humid climates is a bad idea...it reevaporates the condensed water in the pan under the coil, hurting dehumidification.  This makes things LESS comfortable in addition to using juice.

dcheesi

  • Pencil Stache
  • ****
  • Posts: 553
Re: A/C system fan-only = crazy electric bills!
« Reply #16 on: July 15, 2013, 08:46:25 AM »
FYI, the culprit was a bad relay causing the aux heating elements to turn on inappropriately. I eventually had another relay (for the fan) start to go bad as well. Not sure why they all decided to croak, but at least I've got it working now, and I'll know what to look for if it happens again.