Published on September 4, 2026 by Halo Programs
Most HVAC companies choose between the types of direct mail for HVAC work the same way: someone asks the printer for postcards, the printer quotes postcards, and the shape of the piece is settled before anyone has asked what the piece is supposed to do. That order is backwards, and it quietly removes options. The four by six card almost everyone pictures is not eligible for the cheapest saturation product the Postal Service sells.
This article covers the types of direct mail for HVAC companies that USPS actually recognizes as distinct shapes and the dimensions that separate them, what each shape costs you in eligibility rather than just in postage, which piece belongs on which HVAC campaign, how Informed Delivery favors one shape over another, and how to narrow the list without running a year of guesswork.
Why the Types of Direct Mail for HVAC Start With Postal Shape
The Postal Service does not sort mail into marketing categories. It sorts by physical shape, and there are three that matter to a contractor: cards, letters, and flats. Every creative decision you make sits downstream of which of those three buckets your piece falls into, because shape decides the price, the automation discounts, and in one important case whether a mailing product is available to you at all.
The dimensions are not approximate. A card qualifies for card pricing on First-Class Mail at 3-1/2 to 4-1/4 inches high, 5 to 6 inches long, and 0.007 to 0.016 inch thick, and it has to be rectangular. A letter runs 3-1/2 to 6-1/8 inches high, 5 to 11-1/2 inches long, and 0.007 to 1/4 inch thick. A flat is anything that breaks one of those letter ceilings, meaning taller than 6-1/8 inches, longer than 11-1/2 inches, or thicker than 1/4 inch, up to a maximum of 12 by 15 by 3/4 inch.
One consequence surprises people every time. Under USPS Marketing Mail there is no separate, lower price for postcards at all. A card of any size up to 6-1/8 by 11-1/2 by 1/4 inch is simply charged at letter rates. So the small card that saves money on a First-Class drop saves nothing on a bulk marketing drop, and the larger card that gets noticed costs the same as the small one. If you are mailing in bulk, printing small is a design choice, not a savings.
Key takeaway: shape is not a design detail, it is the pricing category. Decide the shape against the postal thresholds before the designer starts, because the thresholds decide which products and discounts you are allowed to use.
Postcards: The Most Common of the Types of Direct Mail for HVAC
The standard postcard earns its popularity. Nothing has to be opened, printing is cheap, production turnaround is short, and the format enforces the discipline of one offer and one call to action. For a dated tune-up promotion going to a list you already own, it is difficult to beat.
Its weaknesses are equally real. There is no room for a second idea, no room to explain anything, and in a stack of saturation mail a small card is the piece physically most likely to be shuffled past. It also cannot carry an insert, so there is no mechanism for the maintenance agreement enrollment form or the co-op branded manufacturer offer that often does the actual persuading.
The EDDM Constraint Most Companies Discover Too Late
Every Door Direct Mail is the reason to get the shape decision right up front. EDDM Retail carries no mailing permit requirement, costs $0.26 per piece, and lets you send at least 200 and up to 5,000 pieces per day per ZIP Code. EDDM BMEU comes in as low as $0.259 per piece but requires a bulk mailing permit. It is the cheapest way to blanket a neighborhood, and it is where most contractor saturation budgets go.
The catch is that EDDM mailpieces have to be flats, up to 3.3 ounces. A four by six postcard is not a flat. It is a card. If your plan is a saturation drop on the routes around a job you just finished, the small postcard is not merely a weaker choice, it is ineligible, and the piece has to be designed at flat dimensions from the start. Companies that design first and ask about EDDM second end up reprinting. The other half of the design decision, what the piece says and the aspect ratio and clear zone standards it has to respect, is covered in the guide to HVAC direct mail ideas.
Oversized Cards and Flats: The Types of Direct Mail for HVAC Saturation
Once a piece crosses into flat territory, it is competing on physical presence rather than on cleverness. That is the correct trade for saturation mail, where your piece arrives alongside every other piece delivered to that address that day and the first job is simply to be the one still in someone’s hand when they reach the counter.
Flats also buy room. A larger surface holds a service menu, a seasonal offer and a maintenance plan offer side by side, a photo of the crew, and a map of the streets you have already worked. For a neighborhood drop following an install, the map is often the strongest element on the piece, because it converts a generic advertisement into local evidence.
The cost is real: more paper, more ink, higher postage than a letter-rate card, and a longer print lead time. Flats are the right tool when you are buying geography and you have no relationship with the household. They are usually the wrong tool for your own customer list, where relevance does the work that size was compensating for.
Key takeaway: flats are for strangers, and the strongest thing you can print on one is proof that you already work on their street.
Letters in Envelopes: The Replacement Conversation Piece
A letter in an envelope is opened less often than a card is glanced at, and read far more carefully when it is. That trade only makes sense when the message needs more than one glance, which in this trade means one thing above all others: the aging system conversation.
Asking a homeowner to think about a five figure replacement is not a postcard job. It needs the install date, the age of the equipment, the repair history you already hold, an honest description of what usually fails next, and a specific number to call. A letter has the room for all of it and the tone to carry it. It also accepts inserts, which is where the financing sheet or the manufacturer rebate belongs.
Letters are worth their higher production cost precisely because the list should be small. If you are mailing a letter to ten thousand households, the segmentation has gone wrong. The aging equipment segment at a typical residential company is a few hundred addresses, it is the highest ticket work on the board, and it is the campaign most often skipped because pulling that list requires knowing which systems you installed and when. That is a customer record question rather than a printing question, and it is why mail programs stall at the seasonal blanket drop. A contractor CRM exists to make that filter a two minute job instead of a project.
Self-Mailers and Newsletters: The Relationship Piece
A self-mailer is a folded piece that travels without an envelope, held shut by a tab or a wafer seal. It sits between the card and the letter: more room than a card, no envelope to open, and depending on the folded dimensions it can land as either a letter or a flat. Check the folded size against the thresholds above, because a piece that is a flat when folded is priced and routed as a flat.
The customer newsletter is the format most residential contractors dismiss and the one that quietly protects the base. Among the types of direct mail for HVAC retention, it is the least urgent looking and the most durable. It carries the seasonal maintenance reminder, a short piece on filter changes or thermostat settings, the names and faces of the technicians, and one modest offer. Mailed two or three times a year to your own list, it keeps you present in the years between a repair and a replacement, which is the whole argument for retention marketing in a trade with a fifteen year equipment cycle.
Newsletters also pair naturally with the digital half of the program. The same content that fills a printed newsletter fills the quarterly send in email marketing for HVAC contractors, at a fraction of the cost per contact, which makes print the deliberate second touch for the households that never open email rather than the only touch for everyone.
Matching Types of Direct Mail for HVAC Companies to Real Jobs
The shape questions above are only useful once they are attached to a campaign. Six campaigns cover most of what a residential HVAC company should be mailing in a year, and each one has a shape that fits it better than the others. Read the list as a mapping from job to piece rather than as a ranking of the types of direct mail for HVAC companies against each other.
Spring and Fall Tune-Up Reminders
Card, mailed to your own maintenance list. The message is a date and an offer, the recipient already knows who you are, and there is nothing to explain. This is the campaign where the small postcard is genuinely the correct choice rather than the default one, and it is also the campaign most worth automating so it leaves on schedule rather than when someone remembers.
Aging Equipment and Replacement
Letter, mailed to systems past ten or twelve years old that you have service history on. Smallest list, largest ticket, highest production cost per piece, and the only campaign on this list where the extra cost is obviously justified by the value of a single conversion.
Post-Install Neighborhood Drops
Flat, by EDDM, on the carrier routes around a completed install. Design it as a flat from the beginning. The piece should reference the work you just did nearby without identifying the customer, and the offer should be a system check rather than a replacement pitch, because these households have no relationship with you yet. Which routes to pick, and what narrowing the list does to your postage tier, is covered in targeted HVAC direct mail campaigns by neighborhood.
New Movers
Card or letter, addressed, to households that recently bought in your service area. New owners have no incumbent contractor and inherit equipment they know nothing about, which makes a first year maintenance offer unusually easy to accept. The list comes from a data provider rather than from you, so the piece has to work without any prior recognition.
Maintenance Agreement Renewals and Lapsed Plans
Letter for a lapsed agreement, card for an on time renewal. A renewal is an administrative reminder. A lapse is a small persuasion problem, and it deserves an envelope and a sentence about what the plan covered.
Winback of Dormant Customers
Card or self-mailer, to customers with no service visit in eighteen to twenty four months. The list is usually larger than owners expect, and the piece needs a reason to return rather than a discount alone. Mail is unusually effective here because a dormant customer has often stopped opening your email without ever unsubscribing, which is why print and digital belong in the same program rather than in competing budgets. Running both against the same customer record is what a combined email and SMS follow-up program is for, with mail carrying the households the screen no longer reaches.
Key takeaway: there is no single strongest piece. Cards serve people who already know you, flats serve people who do not, and letters serve decisions worth more than a tune-up.
Informed Delivery and Which Types of Direct Mail for HVAC Qualify
USPS Informed Delivery emails participating households grayscale scans of the address side of the letter-size mail arriving that day. That is a second impression on a piece you have already paid to send, and it changes the shape calculation in a way most contractors have not accounted for.
The previews are generated for letter-size mail. Flats do not get an automatic scan, so a flat only appears in the preview if you register an interactive campaign through the Mailer Campaign Portal in the Business Customer Gateway, which attaches a color image and a clickable link. That is worth doing, and it is an extra step with a lead time attached.
The practical effect is that a letter-size piece arrives with a free digital preview built in, while a flat needs a campaign registered to get one. If two shapes are otherwise close for a campaign, that tips the decision toward the letter-size piece. It is also the one place where a print campaign and an email campaign land on the same screen on the same morning, so the offer on the mailer and the offer in that week’s email should not contradict each other.
Choosing Among the Types of Direct Mail for HVAC Companies
Narrowing the types of direct mail for HVAC down to one piece is a matter of answering three questions in order, and the order matters because each answer eliminates options below it.
First, does the recipient already know you? If the list is your own customers, relevance is doing the persuading and you can print small. If the list is strangers on a carrier route, physical presence is doing the persuading, the piece has to be a flat, and EDDM is available.
Second, how much does one conversion earn? A tune-up justifies a card. A replacement justifies a letter, an insert, and a list you had to work to build. Matching production spend to ticket size settles most format arguments without a debate about design.
Third, can you actually pull the list the piece requires? This is where most format plans quietly fail. The letter to aging equipment owners, the winback to dormant customers, and the renewal notice to lapsing agreements all assume a customer record that can be filtered by install date, last visit, and plan status. If those filters do not exist, every campaign collapses back into the seasonal saturation drop, which is the one campaign that needs no data at all. That is a reporting problem rather than a mail problem, and it is the same constraint that limits HVAC marketing automation generally.
Once those three answers are settled, production is a logistics question. ContractorHalo’s on-demand marketing covers branded print including postcards and flyers along with an EDDM service, and its automated marketing runs email and direct mail off the one customer database with personalized images and personalized URLs, so the same segment drives both halves rather than two lists drifting apart. For the mechanics of the channel itself, costs, route selection, and match-back measurement, the complete guide to HVAC direct mail marketing covers the ground underneath these format choices, and if you are comparing vendors to produce the piece, how to choose among HVAC direct mail services covers what to ask them.
Frequently Asked Questions
Which types of direct mail for HVAC companies are worth testing first?
Start with two pieces rather than five: a card to your own maintenance list for seasonal tune-ups, and a letter to households whose systems are past ten or twelve years old. The card tests whether your list and offer work at low cost, and the letter tests the highest value segment you own. Add saturation flats only after the addressed half is producing, because saturation is the expensive half and the hardest to attribute.
Can I mail a four by six postcard through EDDM?
No. EDDM mailpieces must be flats of up to 3.3 ounces, and a four by six card is card-size, not flat-size. To use EDDM Retail at $0.26 per piece with no mailing permit, design the piece at flat dimensions from the start, meaning it exceeds 6-1/8 inches high, 11-1/2 inches long, or 1/4 inch thick. This is the most common reason a saturation drop has to be reprinted.
Does a bigger postcard cost more to mail in bulk?
Not in postage, as long as it stays within letter dimensions. USPS Marketing Mail has no separate lower price for postcards, so cards are charged at letter rates. A card up to 6-1/8 by 11-1/2 by 1/4 inch costs the same to mail as a small one. Printing costs still rise with size, but the postage argument for a small card only applies to First-Class card pricing, not to bulk marketing mail.
What types of direct mail for HVAC work in the shoulder season?
The shoulder season favors addressed mail to people who already know you, because demand is not being created by weather. Tune-up cards to the maintenance list, winback pieces to customers dormant for eighteen months or more, and lapsed agreement letters all fit. Saturation flats work better immediately before and during peak demand, when a stranger receiving your piece may already be thinking about the equipment.
Is a letter really better than a postcard for selling replacements?
For that specific message, yes, because the message is long. A replacement decision needs the system age, the repair history, what typically fails next, and a financing or rebate insert, none of which fit on a card. The letter is opened by fewer households but read by more of the ones that open it, and the list should be small enough that the higher cost per piece is not the deciding factor.
Do printed mailers still make sense if we already send email?
They make the most sense precisely because you send email. A meaningful share of any customer list has stopped opening email without ever unsubscribing, and mail is how those households still hear from you. Run both from the same customer record so a household that engages by email is not also receiving the expensive printed piece, and so the offers stay consistent when Informed Delivery puts the mailer and the email on the same screen.
Conclusion
The format question looks like a design question and is actually two other questions wearing a disguise: what shape does the Postal Service think you are mailing, and how well do you know the person receiving it. Answer the first against the published dimensions and you stop losing money to reprints and lost eligibility. Answer the second without flattering yourself and the shape usually picks itself, with cards for people who know you, flats for people who do not, and letters for the decisions worth a real conversation.
The companies that get past a single annual postcard drop are not the ones with better creative. They are the ones who can pull a list of every system they installed before 2015, or every customer who has not called in two years, in the time it takes to make coffee. Build that capability first and the format decisions become straightforward, because each campaign arrives already knowing who it is for.
