What's the difference between nominal and actual size?

Nominal size (e.g., 16x25x1) is the rounded "marketing" size printed on most filters and HVAC slots. Actual dimensions (e.g., 15.5 x 24.5 x 0.75 inches) are the exact physical measurements. They refer to the same filter — manufacturers make filters slightly smaller than nominal so they slide cleanly into the HVAC slot without binding.

How do I find out what size filter my furnace uses?

Pull out your current filter. The size is usually printed on the cardboard frame (16x25x1, 20x25x1, etc.). If no size is printed, measure the slot opening with a tape measure — the nominal size should be ½ inch larger than your slot dimensions in each direction.

Which MERV rating should I pick?

For most residential properties, MERV 11 is the sweet spot. MERV 8 is budget-friendly basic filtration. (We offer MERV 8 and MERV 11 — see the MERV guide for why we skip MERV 13.) See our complete MERV guide for help choosing.

What if my furnace uses a custom or odd size?

We currently stock the most common nominal sizes. If your filter slot uses a non-standard size, contact us — we may be able to source it.

What kind of filters does Filterflow ship?

Pleated synthetic furnace filters in MERV 8 and MERV 11, in the 27 most common nominal sizes, 1" and 4" depths.

How does the subscription work?

Pick the filter size and MERV rating for the property, then choose a pack size — 2 to 12 filters depending on thickness, enough to cover a year of swaps at your reminder cadence. We ship the full pack to the property's address and bill you once per year, when it ships. Between deliveries, your person to notify gets a short text at the cadence you chose (every 1 to 6 months) when it's time to install the next filter — no reordering, no reminders to manage yourself.

Is there a fee to cancel?

No. Cancel anytime from Account → Subscriptions on filter-flow.com. No commitments, no fees, no questions asked.

Can I pause a subscription?

Yes. Pause or resume anytime from Account → Subscriptions — that holds the next annual shipment and charge. Reminder texts for the filters you already have continue; if the unit goes vacant, remove the contact in your dashboard to stop them.

Can I change the filter size or MERV mid-subscription?

Reminder cadence: email support@filter-flow.com and we'll update it right away. The contact we text: change it anytime in your dashboard. Need a different size or MERV? Cancel the current subscription from Account → Subscriptions and place a new order — you're only billed when a pack ships, so there's no double charge. Different address? That's a new property — place a new order for it and cancel the old subscription from Account → Subscriptions.

How much does it cost?

Pricing depends on filter size, MERV rating, and pack size — see the product page for your exact price. Each property is its own subscription, billed once a year when its pack ships. Shipping is free.

Will the SMS reminders annoy my tenants?

No — it's one short text when it's time to swap the filter, at the cadence you chose (every 1 to 6 months), with up to two brief follow-ups if the install isn't confirmed. Nothing starts without their say-so: every contact confirms by text or email before the first reminder is ever sent, every message identifies FilterFlow, and they can reply STOP at any time.

What does the SMS message say?

The reminder reads: "FilterFlow: Hi [first name], your replacement filter has arrived. Please install it, then confirm: [link]." One tap on the link confirms the install. If it goes unconfirmed, they get up to two short follow-ups — and either way, you get a text telling you whether the filter was installed, so you're never left guessing.

What if my tenant doesn't install the filter?

We send up to two polite follow-up texts two days apart. If the install still isn't confirmed, you (the landlord) get notified so you can follow up directly. No tenant-chasing required on your end. If a skipped filter ever damages the furnace, here's when you can charge a tenant for damage from a dirty filter.

Who's responsible for changing the filter, the landlord or the tenant?

Usually the landlord, unless the lease assigns it to the tenant in writing. See who changes the furnace filter in a rental for what the law says, and use our free tenant air filter lease addendum to put it in writing. Rules vary, so check your state.

Do I need to give Filterflow my tenant's phone number?

Yes — that's how the SMS reminder works. We treat tenant contact info as confidential and never share it. Tenants can opt out of messaging without affecting the subscription.

What if there's no tenant — the unit is vacant?

Remove the contact for that property in your dashboard and reminder texts stop. When someone new moves in, add them as the contact — they'll get a one-time text and email to confirm, and reminders pick back up from there. The annual filter shipment continues either way; pause it from Account → Subscriptions if you don't need it.

How long does shipping take?

Typically 4–7 business days via FedEx. You'll get the tracking link in your order email and dashboard. Your contact isn't texted until it's time to install.

Where does Filterflow ship?

Anywhere in the contiguous United States — the lower 48 states plus Washington, DC. We don't currently ship to Alaska, Hawaii, US territories, or international addresses.

Is shipping included in the subscription price?

Yes. Free shipping on all subscription orders.

Can I ship to multiple addresses from one subscription?

Each property gets its own order and subscription, shipping to that property's address. Manage them all from one account — place one order per property and everything shows up together in your dashboard.

Can I order for multiple properties in one checkout?

Place a separate order for each property — every order ships to one delivery address, and install reminders are tied to the property at that address. Multiple filters for the same property (two furnaces, a duplex)? Add them all to one order.

What if a pack arrives damaged, or isn't the size I ordered?

Email support with a photo of the pack and label within 14 days and we'll ship a replacement at no charge. Those are the only cases we replace or refund — all other sales are final, so double-check your size before ordering (see the sizing question above).

Can I manage multiple properties or units?

Yes. Place an order for each property. Each unit has its own size, MERV rating, shipping address, and contact. All managed in one place, each billed separately when its pack ships.

Can I add a property manager or co-owner to my account?

Multi-user accounts are on our roadmap. For now, sign-in uses a one-time code sent to the checkout email — a co-manager with access to that inbox can sign in the same way.

How are properties organized in the dashboard?

Each property you've ordered for shows in your dashboard with its filter, reminder cadence, contact, recent reminder texts, and order history.

How do I update billing info?

Account → Subscriptions → payment method.

Still have questions?

If you don't see your question covered above, we're happy to help.