FAQ
Frequently asked questions
Sizing, MERV ratings, change intervals, delivery, and cancellation. If the answer you need is not here, email or call — the number on this site reaches a person.
How do I find out what size filter I need?
Pull out the filter you have now and read the size printed on the cardboard frame — it will look like 20x25x1 — and if the frame is unreadable or missing, measure the opening and use the size finder.
The number printed on the frame is the nominal size, which is the size you order by. Almost every filter frame carries it on the long edge in large type.
If there is no filter in the slot, or the frame has gone soft and unreadable, measure the opening itself and round to the nearest common size. The filter size finder walks through it in three steps.
Why is my filter smaller than the size printed on it?
That is normal and expected — filters are sold by nominal size, and the actual measured size is typically about half an inch smaller on width and height so the filter can slide into its track.
A filter labelled 20x25x1 generally measures closer to 19.5 by 24.5 inches, and a nominal 1-inch filter usually measures about three quarters of an inch thick. It is not a defect and it is not a different filter.
Order by the nominal number printed on the frame. If you measured the opening rather than a filter, round to the nearest common nominal size rather than ordering the exact measurement.
Which MERV rating should I choose?
MERV 11 for a 1-inch slot and MERV 13 for a 4-inch or 5-inch media cabinet, unless an HVAC tech has measured your system's static pressure and recommended something different.
MERV 8 is mostly equipment protection — it keeps the coarse material off your blower and coil but passes most of what stays suspended in the air. MERV 11 captures meaningfully more without an airflow penalty ordinary residential systems notice.
The full comparison is on MERV ratings explained.
How often should I change my filter?
Every 60 to 90 days for a 1-inch filter as a baseline, dropping to 30 to 45 days during spring pollen and ragweed season, and every 6 to 12 months for a 4-inch or 5-inch media cabinet filter.
Charlotte's long cooling season means the blower accumulates more hours than the national average, and hours are what load a filter. Treat the 90 days printed on the sleeve as a ceiling rather than a target.
The month-by-month version is on the filter change calendar.
How do I know if my filter needs changing right now?
Hold it up to a light — if you cannot see light through the pleats, change it.
A new pleated filter is translucent between the folds. As it loads, that translucency disappears, starting on the intake face. The light test beats the date on the frame because it measures the thing that actually matters.
Will a higher MERV filter damage my system?
It is unlikely on a modern system with adequate return ductwork, but a higher rating does present more resistance to airflow, and on a system that is already restricted that can reduce airflow enough to cause problems.
The larger risk in practice is a filter of any rating left in past its service life. A loaded filter restricts airflow far more than a clean higher-rated one.
If your house has a single small return serving a whole floor, ask an HVAC tech to measure static pressure across the air handler before moving to MERV 13 in a 1-inch slot.
Which way does the arrow on the filter point?
The arrow points in the direction the air is moving — toward the furnace or air handler, away from the return grille.
At a wall or ceiling return, the arrow points into the wall or ceiling. At a furnace slot, it points toward the furnace itself.
A filter installed backwards still filters, but the media is built to load from one side, so it will not last as long or perform as designed.
Does it matter if the filter does not fit the slot tightly?
Yes — air takes the easiest path, so a gap around the frame lets unfiltered air bypass the media entirely, and a well-fitted MERV 8 outperforms a MERV 13 with a half-inch gap down one side.
If your current filter rattles in the track or leaves a visible gap, you may be running a size that is close but not correct. Measure the opening and check it against the size list.
How do I tell a 1-inch filter from a 4-inch or 5-inch one?
A 1-inch filter slides into a thin slot behind a wall or ceiling grille or at the furnace, while a 4-inch or 5-inch filter pulls out of a hinged metal box bolted to the air handler.
The metal box is called a media cabinet, and it is usually installed with the system rather than added later. If you are opening a hinged door to get the filter out, you have one.
Both are listed separately on the catalog page, grouped by depth.
Where do you deliver?
Charlotte and the surrounding towns: Charlotte, Matthews, Mint Hill, Pineville, Huntersville, Cornelius, Davidson, Concord, Indian Trail, Waxhaw, and Belmont.
If you are just outside that list, get in touch — the service area is drawn around Charlotte and Mecklenburg County, and the edges are a question of routing rather than policy.
Can I order right now?
Not yet — the catalog is published and the sizes are set, but ordering is not open, so the button on each size page adds you to the launch list instead.
There is no cart and no checkout on this site on purpose. When you use the notify button, it opens an email with the size and cadence you selected already filled in. Send it and you are on the list for that size.
You can also just email zach@piedmontfilters.com or call (704) 237-0572.
Are the prices on the site final?
No — every price shown is a placeholder while supplier pricing is being finalised, and each one is labelled as such on the page.
Rather than hide pricing entirely, the site shows the structure of it — per filter, per delivery, and per month at each cadence — so the shape of the offer is clear. The numbers themselves will change.
Do I have to subscribe, or can I order once?
Both will be available — a subscription on a 1, 2, or 3 month cadence, or a single one-time order with no ongoing commitment.
The subscription exists because the failure mode with filters is forgetting, not cost. Having the right size arrive on the right month solves the actual problem.
The full comparison is on how it works.
How do I cancel or change a subscription?
By email or phone, with no minimum term and no cancellation fee.
Skipping a delivery, changing cadence, changing size, or stopping entirely will all be handled the same way: tell us, and it is done. There will be no retention flow and nothing to click through.
How do the filters get to me?
They arrive at your door in a flat box sized to the filter, with no signature required and nothing to be home for.
Filters are light and awkward rather than heavy and fragile, so the box is large and thin. It fits behind a storm door or on a porch.
Do you install the filter for me?
No — this is a delivery service, not an HVAC contractor, and changing a filter is a task that takes about a minute once you know where the slot is.
If your system needs actual service — measured static pressure, a duct evaluation, or anything involving the equipment itself — that is a job for a licensed HVAC contractor, and it is worth having one you trust.
What does an air filter actually do?
It captures airborne particles from the air passing through your HVAC system — dust, pollen, pet dander, fibers, and, at higher MERV ratings, finer combustion particles.
That is the entire claim. A filter is a particle capture device sitting in the one place in your house where all the air goes past a single point.
It does not remove gases, odors, or ozone, and no MERV rating changes that. Those require a different mechanism, usually activated carbon.
Who runs this?
Piedmont Filter Co. is run by Zach Towers in Charlotte, operating as Piedmont Filter Co. LLC.
The about page has the longer version, including why this exists here rather than as another national subscription box.