Hvac air filters

[Curmudgeon44]

I'm surprised that someone doesn't make a simple manometer to measure the air pressure loss across the filter. It seems like it would be a lot more objective than holding the filter up to the light.

I have installed a manometer to monitor how long it takes for the pressure drop to get too high. In my house the answer is almost forever. This was after many months of following a discussion board populated by HVAC professionals. They did indicate a filter would work more effectively as it loaded up... a high end Honeywell model thermostat can actually measure the energy to push air, and therefore tell you when the filter becomes too restrictive from accumulated dirt.

Many of them badmouthed high MERV filters because so many duct designs were already restrictive and could not function well with the added pressure drop of that kind of filter. But almost nobody measured this, they tended to adopt a narrative and apply it as if all houses were the same. Sorry to say math is not their strong point.

If you want to simplify down to one variable, have lots of filter area so filter face air speed is lower... then your pressure drop will be low, probably your air flow better, and the parts will work better together. My house has added filter grilles to achieve this.

Hope this helps.

 

[ERD50]

Following the filter replacement instructions costs much less than the HVAC accidentally getting messed up and it'll be WAY more expensive.

Not necessarily, which is why this is being discussed.

It's not "one size fits all". But "the filter replacement instructions" mentioned in the OP say to replace every three months. But some of us barely run the HVAC in spring and fall, while it's running many hours/day over the winter. Very difference usage over those different 3 month periods.

Waiting to see some minor build up before changing the filter will *not* lead to a 'messed up' HVAC and expensive repair. It's dirty when it's dirty, it's not mandated by a calendar date. Conversely, waiting 3 months to change it if it gets clogged (pet hair?) in one month *could* lead to stress on the motor.

-ERD50

 

[Sunset]

I write on mine when I install as I can't remember otherwise. I just use a permanent marker.
I try to change it every 4 months, but since we turn off the system in Spring and Fall it doesn't get dirty during those times.

I upgraded to a merv 8 or 11 from the cheap blue fiberglass ones. The cheap blue ones would stop dog hair but not much else.

 

[Buckeye]

They do. See:

skip to about 3:30

But many people have the ability to measure amperes with a hand held DVOM that they already have. The more amps the fan motor is pulling the higher restriction of the filter.

This is a great video. The guy doing the video (total A/C nerd, ) was surprised how low the initial pressure drop was for the higher (1900) MPR filter, actually lower than lower MPR filters.