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My HVAC filter is in my crawlspace and is a hassle to change. I don't want to change it more than needed. "Change it every month" is bogus advice because in some months (like May) we don't have to run the HVAC at all.

I'd like a thermostat with a filter-change reminder that is based on how long the filter has been in use, not how long it has been installed. That is, I'd like only the time when the blower is on to count against the filter's lifetime. Is there a product like this?

For instance, does this unit count time in this way?

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The filtrete unit you linked to is just install time, not run time. –  Steven Jun 6 '12 at 17:11
"Change it every month" means "Change it every month (the unit is in service)". For example, if you only use the unit during cold months (for heat), you don't have to change the filter at all during the warm months when the furnace is not used. –  Tester101 Jun 6 '12 at 17:21
@Tester101, what is the minimum run time in a given month to consider that an in-service month? –  ArgentoSapiens Jun 6 '12 at 17:40
@ArgentoSapiens Not sure. Depends on your furnace, indoor air quality, cleanliness of the duct system, etc. The best advice is "When the filter is dirty, change it.". Though I can understand that's not the most welcome advice in your situation. –  Tester101 Jun 6 '12 at 17:52
I think the reason they don't do this is exactly what Tester101 is saying: When it's dirty, it needs to be changed. Without being able to directly measure if it's dirty, all you can do is estimate. Air quality is by far the biggest factor, and the amount of runtime is entirely based on the air quality (eg, if the air was 100% clean, the filter would theoretically never need to be changed). While measuring runtime is going to make things more precise, it will not be more accurate, so there is no point in spending effort on this function. –  gregmac Jun 6 '12 at 19:27

3 Answers 3

up vote 5 down vote accepted

Some programmable thermostats do base their filter reminder on run time. However, the problem is looking at a filter, their change out period is not mentioned in runtime, it just says 'every 6 months' or something like that, so it's a little tricky to convert sometimes.

The Radiothermostat 3M-50 (in your link) says:

FILTER - AIR FILTER ALERT - The 3M-50 can be programmed to remind you when the HVAC sytem’s air filter needs changing. Touch FILTER. The display will show the usage to Touch FILTER for over 3 seconds and the display will change to LIMIT. Touch arrows to set desired usage limit before filter alert comes on home screen. When this limit is reached, FILTER will be on home screen and the CHECK FILTER indicator lights. Limit may be set from 0 to 999 days/99 weeks; default is 90 days/12 weeks. Touch to reset. To reset the usage back to 0, touch usage number

However, I recently installed a Trane Z-Wave thermostat and its filter reminder is based on hours. As a bonus, you can implement Z-wave in your house!

The Filter Service screen will show the accumulated Filter Runtime hours as well as the Service Interval that will be used to trigger a filter message. Any type of HVAC operation that causes the HVAC system fan to run will cause the Filter Runtime value to increase.

Trane Z-wave thermostat

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Aaron, that makes a lot more sense. What other Z-Wave devices do you have? Which controller do you use? –  ArgentoSapiens Jun 6 '12 at 18:52
@ArgentoSapiens I haven't had the chance to really play with it a whole lot, but you can drop by the chat and we can discuss if you'd like... –  Aaron Jun 12 '12 at 17:10

I have a Hunter model 44550 (also known as Auto Saver 550). It tracks actual run time, displays run time (today, yesterday, this week, last week, since reset), and flashes FILTER after 500 hours of run time. (The 500 hours for filter reminder cannot be changed.) The model has been around for about 15 years but is still available.

Unfortunately I'm looking for a replacement, as the temperature sensor has just broken. The unit is 13 years old, so I have no complaint about reliability. OTOH, I no longer have much use for programmability, much less 7-day -- just makes it harder to set back when I go out of town. Otherwise, though, I can still recommend it -- and unless I can find another that has all the time features, I may well replace it with the same model anyway.

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Talk to your HVAC service tech about installing a remote magnehelic gauge. They cost less $100 and you can probably install it yourself. When the fan runs it creates a vacum in the space between the filter and the fan. This pressure difference can be measured by the gauge. The higher the reading the dirtier the filter. You can experiment with how dirty you want the filter to get before you change it and note the reading on the gauge. The filter manufacturer may have information on when to change based on the reading.

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