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 80+ 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 with a recyclable beverage-board frame. All filters meet ASHRAE 52.2 standards for their MERV rating.

How does the subscription work?

Pick the filter size and MERV rating for the property, then choose a pack size — 2, 4, 6, or 12 filters, 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, 2, 3, or 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 your account dashboard. No commitments, no fees, no questions asked.

Can I pause a subscription?

Yes. Pause for a specific number of months or indefinitely. Resume anytime. Useful for vacant units or seasonal properties.

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

Yes. Update size, MERV, cadence, or shipping address in your account. The next shipment will reflect your changes.

How much does it cost?

Pricing varies by filter size and MERV rating. Subscription pricing is typically 10–15% less than one-time purchase. Multi-unit discounts apply when you manage multiple subscriptions from one account.

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, 2, 3, or 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 after a few days. 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.

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?

Pause the subscription, or update the unit's "occupied" status in your dashboard. When occupied, you can update the tenant contact info anytime.

How long does shipping take?

Typically 3–5 business days from US warehouses. You'll receive a tracking link via email and the tenant gets one via SMS.

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 filter arrives damaged?

Email support with a photo within 14 days. We'll ship a replacement at no charge.

Can I manage multiple properties or units?

Yes. Add as many units as you need from your account dashboard. Each unit has its own size, MERV rating, shipping address, and tenant contact. All managed in one place, billed together.

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

Multi-user accounts are on our roadmap. For now, you can share account credentials with a co-manager or contact us about a managed account if you're operating at scale.

How are properties organized in the dashboard?

Group units under a property name (e.g., "Maple Street Apts"), then within each property add individual unit subscriptions. View all units at a glance, including filter status, last shipment date, and install confirmation status.

How do I update billing info?

From your account settings → payment methods. Changes apply to all future shipments.

Still have questions?

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