Tough call.
Filters actually filter better when dirty, but refrigeration systems need the most airflow.
Filters impede airflow when they are clean so you can imagine that even invisible captured debris can begin to cause problems.
Most importantly with warranty verbage failure to follow instructions could cost you more than the price of a filter.
I do not adhere to the guidelines strictly and your installer may not either. Why don't you ask him/her.
Joe

TechGromit,

Compared to the cost of your system, filters are VERY CHEAP. Taking care of your filters is the one thing you, as the homeowner, can do to help insure your heat pump runs as efficiently as possible, for as long as possible.

In the HVAC business about 25% of my service work is due to neglected filters. A $90.00 service call buys a LOT of 1" filters!! We had to replace the compressor in a unit that was only a year and a half old because the owner never once cleaned his filter. The factory WOULD NOT cover the repair under warranty, costing the homeowner several thousand dollars!

Play it safe and protect your investment...

Bergy

The 4 inch filters I have run about $25 each, but your point is taken.  I've been keeping an eye on them, I just didn't see the need to replace something that looked clean to me. Invisible debris? I would expect to see at least something when I held it up to the light. I'll compromise and replace them every 6 months, unless I see that it's dirty before then.

On that system you repaired, was the filter obviously dirty?   

I'm sure I kow the answer to this question, but being a tight wad that I am, can filters be cleaned with compressed air and reused? (provided of course you don't blow a hole thru them). Obviously you have re-install them correctly, just flipping the filter around to the clean side proably isn't a good idea. :)

Tech, where do you buy your filter? Lowe's is cheaper than Home Depot. I was buying it from HD since it's closer to us for about more than $7 per piece ( I always need 2 - 14x30x1) and they run out of this size. I went to Lowes and so happy to buy half that price..so I bought another 2 to last me for another 6 months.

I ordered them online, I picked up a case of 4, Mine are 24x20x4,  at lowes by the case $226.71 (of 6)  that's $37.88 each.  I think I got mine for $22 each with free shipping if the order was over a certain $ amount. That's why I picked up 4.  I seen another website that sells the same size for under $18 each, but I don't know what the quality of the filters are.  I ordered the same filter brand that came with the unit, so I'm assuming it's a pretty good one. 
 
I see they sell your 14x30x1 filters for $32.95 for a case of 12, that's $2.75 each. Perhaps you should reconsider where you getting your filters from.  You might have to order several cases to get free shipping. If space is an issue, perhaps you can get just one case. In my house I could get 50 cases and easily lose store them since so much of it's un-used.
 
 

That's neat Tech! can you give the website? I will order them....I only change them every 3 months..I hope that's the same as what I am getting..kindly send me the website to look. Thanks Tech!

TechGromot,

As a filter becomes dirty, the fan MUST work harder to over come the restriction. The fan will pull particles through the filter and begin depositing them on the coil and on the fan blades, lowering it's ability to move air.

Our filters are permanent 1" electrostatic filters. We always recommend that our clients wash them monthly. While every home's filtration needs differ, If you get into the habit of replacing them before you think they need it you will do yourself a favor.

Bergy

Thank you, Point taken. I took a look at the installed filter tonight and compared it to a new one. It was an off white color when compared to the new white one. Perhaps I'm expecting them to be more dirty then they really get under normal operating conditions. I replaced it tonight, thanks.

 

 

What does your installer say?
J

Tech I am in the same boat as you. I hate replacing an "unused" filter. I ended up putting in a .5 inch Magnehelic gauge just after the filter. So basically it tells me the negative pressure after the filter. The more it is plugged the higher the suction. I took readings with a clean filter and have been watching them. After 6 months they went up about .15 inches in the "normal" A/C speed. The last time our HVAC guy was out I showed him the gauge and he said about .2 inch at that speed would be "dirty". So now I know.

I bought the gauge used on e-Bay for about $50, but since our filters are $30 or so each (24x20x5) extending the filter changing time by a couple months should pay for itself and more importantly give me piece of mind knowing how the filter is doing. I also see things like when they sheet rocked and plastered our basement last month, the pressure went up noticeably in a week and I waited about a week for things to settle out and changed the filter.

I would think a gauge like this with simple markings on it as to when to change the filter would help end users a LOT something as simple as a swing arm based on air flow could be rigged up, again being a visual cue for owners to change the filters out.

Note that ECM blowers will maintain airflow through a clogged filter up to their rated static pressure, albeit at increased power and noise, so a swing arm would indicate low flow too late. pressure drop across filter is better.

Some air source systems (high end Carrier Infinity??) have the ability to measure the drop and annunciate a reminder at the thermostat