How old is my Heil furnace or air conditioner?

By Dana Whitlock. Updated October 2026. Widely documented.

Heil has been on furnace cabinets long enough that older ones say Heil-Quaker. The date sits in characters two through five, two digits of year and then two of week. A serial starting L00 41 came off the line in week 41 of 2000.

Heil is one of the oldest names in the International Comfort Products family. Plates from the late 1980s onward all use this layout. Very old Heil-Quaker units with a different serial style are outside what the tool reads.

Where to find the label on a Heil furnace

On a Heil furnace, open the upper burner door or lower blower door and look for a silver or white plate on the inside wall or the back of the door. Heil condensers and heat pumps put the plate on the cabinet itself, often on the corner panel near the refrigerant lines and electrical disconnect. Turn the furnace off at its switch first. Read, don't reach. Line of sight and a flashlight are all you need. If the plate is greasy, a dry cloth on the plate itself is fine.

How to read the code

A Heil serial is usually ten characters: one letter for the plant, two digits for the year, two digits for the week, then a five or six digit sequence. Years 80 through 99 belong to the 1900s and 00 onward to the 2000s. Week numbers run 01 to 52, sometimes 53. The tool converts the week into an approximate month. Note the order: year first, then week. Payne and Carrier serials, even though Carrier owns Heil's parent company, put the week first.

Real serials in this code

When the format changed

CPSC's 2005 recall of ICP packaged units, which listed Heil among eight brand names, described the serial as appearing in the typical format L004112345 and covered units built from the 41st week of 2000 through the 26th week of 2003. That notice is the cleanest public proof of the year-then-week order. Earlier ICP and Inter-City labels that use a single year digit, an all-numeric string with a letter in the middle, or a Z prefix are not decoded here. If your Heil serial looks like one of those, check the plate for a printed manufacture date or use the installation paperwork.

Who makes Heil

International Comfort Products, headquartered in Lewisburg, Tennessee, builds Heil. Carrier agreed to buy ICP in 1999 and kept its brands and distributors running as a separate subsidiary. ICP describes Heil as a brand dealers have recommended for more than 50 years. Sister brands Tempstar, Comfortmaker, Arcoaire and KeepRite come out of the same operation and use the same serial format, so a Heil and a Tempstar built the same week will show the same date digits.

How sure is this?

Widely documented. Heil doesn't publish this code; it comes from recall notices, service literature and inspector references. We tested the icp rules against 15 serials, 5 of them with a date known from a recall notice, a printed label date or the maker. None decoded to a wrong year; codes whose year mark repeats show every possible reading. Always confirm with Heil's warranty page before you spend money on the answer.

Quick notes

• Register a newly installed Heil within 90 days; ICP drops the parts warranty to 5 years if you miss it.
• A Heil serial that starts with a digit is probably a different brand's label or a misread; check the plate again.
• Packaged rooftop or side-yard units are the ones the 2005 recall covered; if yours dates from late 2000 to mid-2003, ask a dealer whether the repair was done.
• A Heil and a Tempstar built the same week show the same date digits, so any ICP dealer's chart reads Heil plates too.