Originally Posted by
mixer440
Filter Sizes
I'm baffled by the range of choices for furnace filters.
A new furnace that I'm having installed will have a custom built 20x20x4" media cabinet. But looking around, I'm seeing that the 4" filters are actually undercut to around 3 3/4"...which I assume will fit in my cabinet. To make matters even more confusing, there are some "so called" 4" filters that are really 4 3/16" to 4 3/8" that evidently are for the Honeywell cabinets. Not sure though. Where I'm really confused is that the 4" undercut filters seem to be pretty generic and not the best quality, again I think. Is the 3 3/4" size even standard so you can pick one up at a local store ?
Merv Ratings
I'd like a better Merv rated 4" filter....say around a Merv 10-13, but I'm worried about 2 things:
1. Air resistance. Will it even work, or will it slowly destroy the furnace ?
2. Is it realistic to change a Merv 10-13 filter every 6 months ?
If not, then perhaps I should stick with the cheaper Merv 8's and change them more often ?
The "average" filter will have dimensions a little smaller than the listed size. This probably is due to them wanting to make sure they fit into the vast majority of cabinets. The branded ones will be bigger because they are designed from the start as proprietary items that can only be purchased from specific outlets like the dealer that installed the filter rack/box.
Air resistance can become an issue if the original install was not designed around the restrictiveness of the filter at the time to change it.
When to change any filter is up to you and your home. The higher the Merv rating the more likely it is become full quicker because it is capable of stopping smaller particles. It all depends on what is floating around in the air in your home.
If you want to know exactly when to change your filter you need to install a differential pressure gauge across the filter. When the pressure drop gets to the predetermined amount..... change the filter.
Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.