Fan duration to determine when to change filter

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I don't need a complex programmable thermostat. All I want is to know how many hours that fan has run so I know when to change the air filter. The fan runs frequently in the summer and winter, but very infrequently in the spring and fall. How often the fan runs is determined by temperature. You can go weeks - or months - without the fan running at all.
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On Sunday, November 15, 2015 at 6:44:05 PM UTC-5, Chicago Bob wrote:

All you need to do is keep track of the fan hours while checking the filter every now and then. Once you notice that it needs to be changed, you'll know how many hours of fan operation it takes. From then on, all you need to do is keep the amount of dust in your house exactly the same over those hours of operation and you can change the filter based on run time.
Good luck with that.
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On Sun, 15 Nov 2015 15:54:46 -0800 (PST), DerbyDad03

The programmable thermostat is meant for someone who leaves the house empty when he goes to work, and/or who wants to save on heat or AC when he's sleeping. In order to save money and conserve fuel.

I like your idea but I'd make it even simpler than this. Just keep track of the weeks or months while checking the filter every now and then.

Once you notice it needs to be changed, you'll know how many months of operation it takes.

I think you were sarcastic here, but I still like your idea.

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On Monday, November 16, 2015 at 8:15:12 AM UTC-5, Micky wrote:

The entire post was sarcastic. The idea behind "keeping the dust constant" has to start with knowing how many hours of time it takes before the filter needs changing - at that dust level. That is why my process was posted as a single paragraph. You can't do one without the other.
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Chicago Bob wrote:

You never turn the fan on for like circulating air or freshen up the stale indoor air specially when cooking, etc.? Filter gets dirty not only depending on how long fan ran, it also depend how much dust is generated indoor if there is pets, plants... I'd think under replacing it may be a bad idea. I'd rather over replace. My filter size is 16x25x5. I replace twice a year. They don't look too bad when pulled. But It gives me peace of mind. Programmable saves energy depending on how you use it. I use it in my house and out at cabin.
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With just me and the wife at home and no pets and we keep the windows closed there is not much dust and dirt. I use the least expensive 20x20x1 filters and change them every 2 months on my heat pump. Most of the time they seem to be just about as clean as the new ones. At less than $ 10 per year it is not worth me worring about. Just change them on the odd numbered months at the first of the month. Some months it runs a lot and some not too much, but I just keep on schedule. Not worth the trouble to keep up with how dirty they get.
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You need to put a run time meter on the fan motor.
Get one like this from China. I have ordered several items from China and it usually takes 2 to 3 weeks. They all have worked fine.
Ebay number: 111229090029
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On Sunday, November 15, 2015 at 6:55:03 PM UTC-5, Ralph Mowery wrote:

What purpose will a run time meter serve, other than recording the run time?
His goal is not attainable unless he can keep the amount of dust being trapped by the filter constant over any given fan run time. That ain't going to happen.
Methinks he knows that. He's just being silly.
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I don't know what his goal is, he said "All I want is to know how

So with that I gave him a place to get a 120 volt run time meter.
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On Sunday, November 15, 2015 at 7:17:12 PM UTC-5, Ralph Mowery wrote:

Does that not tell you that his goal is to change the filter based on fan run time?
I'm sure you know that that is a not the best way to determine when to change the filter.

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DerbyDad03 wrote:

Really? Then how come most topics in this NG drag out SO LONG wasting time and band width? There are many with simple mind and tunnel vision.
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On 11/15/2015 4:44 PM, Chicago Bob wrote:

How many "fan hours" do you consider significant? For an arbitrary (and possibly seasonally variable) figure, you could buy an elapsed time meter and wire it in parallel with your fan motor. Or, you can buy a cheap clock (with date indication) and use that (i.e., change it when N days have elapsed since the date displayed on the previous change -- I suspect if you're off by a few fan-hours it's not going to matter to you!)
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Chicago Bob wrote:

Fan run time is only one factor. There are other fctors like type of floor in the house, pets, palnts, new or old house, etc. I just replace twice a year.
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On Sunday, November 15, 2015 at 7:42:56 PM UTC-5, Tony Hwang wrote:

In my opinion, fan run time isn't even a factor. Taken to the farthest extreme, in a 100% dust free environment, the fan could run forever and the filter would never need to be changed.

Those are the factors that matter.

Since that works for you, it's perfect. I use a reusable filter and my fan runs 24 x 7, so it needs to be "changed" more often. I also have a dog and cat. I take the filter out at least once a month and use my electric leaf blower to blow the dust out in a "reverse air flow" manner.
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DerbyDad03 wrote:

If I want to use reusable I throw in electronic cleaner elements. I can just wash them in the DW. Filter box is perfect for E. cleaner or 25x16x5 pleated cartridge. Just two of us and large dog. Last cat died from natural cause. Decided not to have another cat who may outlive us.
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On Sunday, November 15, 2015 at 11:24:21 PM UTC-5, DerbyDad03 wrote:

I see your point, but the OP isn't the only one that thinks fan run time is relevant. I've seen thermostats from major manufacturers that have a filter indicator that goes on based on hours of fan run time. I've never bothered with it though. Like you, I just check and/or change based on length of use and past experience.
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On Monday, November 16, 2015 at 7:45:13 AM UTC-5, trader_4 wrote:

I'm one who thinks run time is a useful measurement. It gives you the best indication whether your equipment is sized properly, and that will let you be sure of the right size when it comes time to replace.
I'm not sure how useful it is for filter replacement. I do that by listeni ng to the air flow across the filter - when it starts to get a bit louder I replace. When my hearing fades (I'm getting up there in age) I'll just st art changing every two months again.
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On Monday, November 16, 2015 at 8:18:21 AM UTC-5, TimR wrote:

st indication whether your equipment is sized properly, and that will let y ou be sure of the right size when it comes time to replace.
What does a thermostat's run time tracker actually measure? If all it measu res is *fan* run time, it will tell me nothing about whether my furnace is sized correctly o r not.
I often run my fan 24 x 7 to keep the air circulating.

ning to the air flow across the filter - when it starts to get a bit louder I replace. When my hearing fades (I'm getting up there in age) I'll just start changing every two months again.
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On Monday, November 16, 2015 at 5:56:20 PM UTC-5, DerbyDad03 wrote:

And if all it measures is compressor time, it will tell you very little about your filter.
But I don't really care about the filter. I change it by the time, or when I hear the air flow sound change, whichever comes first.
I don't have a thermostat with a run time tracker and in fact have never seen one. So we need someone to tell us how they are programmed. In theory I don't see any reason why they couldn't track either fan or compressor, or both.
If your AC equipment is running 10% of the time on a hot day, it's too big. If it's running 100% on a mild day, it's too small. Ideally it would run 100% on your peak days and not quite keep up.
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On Tuesday, November 17, 2015 at 8:24:20 AM UTC-5, TimR wrote:

I've had a programmable where it tracked fan time. It was specifically there for what the OP is talking about, it's the filter change reminder. You could set the number of hours, it counts down, when it expires it puts up a flashing filter change indicator.
Never saw one that tracked furnace or compressor run time. The filter change angle is the only real use I see, based on fan time.

Say what? Run 100% on peak days and not keep up? Who would want that? Also, with undersizing it's not just the keeping up, it's the recovery time. I want a system that doesn't take all day to heat or cool the house and get it back to desired temp when it's been setback.
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