ANSI Standard Z83.18 Recirculating Direct Gas-Fired Industrial Air Heaters, which covers any unit that might use recirculated air for part of its operating range, was substantially revised earlier this year. However, some say the new standard is causing confusion for HVAC engineers and building code authorities.

As of January 1, 2003, manufacturers who wished to abide by the new standard had to make some significant changes to their equipment. They were also required to place more complete information on a unit’s nameplate, including certified capacities, inputs, maximum temperature rise, and discharge temperature.

Many manufacturers scrambled to become fully compliant by the deadline, spending hundreds of thousands of dollars on research and testing. Now, with certified equipment labeled and ready to go, some manufacturers are concerned that engineers, contractors, and local code authorities don’t seem to know what to do with it.

They cite instances where specifications are being written to the older version of the standard, and note that many building inspectors see an ETL label on a unit and assume it’s compliant, even though the equipment may be certified to the old standard.

Some wonder who should be educating the affected industries about the changes: ANSI? Testing agencies? Manufacturers? Trade associations? Of course, the answer depends on who you talk to.

What Changes Were Made

There are some big differences between the previous version of Standard Z83.18 and the new version. These changes primarily apply to flame safeguard systems, gas train components, airflow sensing, labeling, and most importantly, the emission levels and combustion testing of the equipment. All of these changes deal with safety and, to an extent, reliability, said Robert Jauch Jr., general sales manager for AbsolutAire, Inc.

One of the biggest changes between the old and new standard is that under the old standard, engineers could specify a direct-fired recirculation unit as long as they provided a minimum of 4 cfm of outside air for every 1,000 Btuh of heat provided.

On January 1 of this year, it became necessary for the unit to operate in compliance with a sliding scale of outside air vs. “equivalent temperature rise.” The greater the temperature rise, noted Mike Kaler, marketing manager for Applied Air, the greater the amount of outside air required by the standard.

Units must also be self-regulating or “adaptive.” “They must be able to vary the amount of outside air, or the temperature rise, or both, in order to keep the unit in compliance at all times. The required amount of outside air could fluctuate from 100% down to as little as 10% or 15% depending upon the temperature rise through the burner section,” said Kaler.

Allen Pirro, chief engineer for Intertek Inc., which tests equipment for the ETL mark, noted the revision addressed concerns about the testing methods to ensure that the heaters, when operated in the recirculating mode, would not produce amounts of CO and NO2 in excess of national standards. “It meant some redesign and retesting to verify compliance.”

Jay Schmidt, sales and marketing manager for Greenheck’s makeup air division, said that the testing procedure has definitely become much more rigorous. “You now test at the extremes. With the old standard, you tested at a nominal burner pressure drop or a nominal velocity and at the minimum airflow. With the new standard, you actually test at the minimum and maximum airflow switch trip points, which means you’re on the outer limits of where you say your unit can operate, so it’s a lot harder to pass the standard.”

James V. Dirkes II, P.E., vice president of Rapid Engineering, said the significant changes between the old and new standards can be summarized as follows:

  • All outdoor air must be provided integrally to the air handler (the previous standard allowed outdoor air to be introduced by a separate means, such as an exhaust fan and inlet louver);
  • Combustion testing is much more rigorous, especially interactions between the mixing dampers and combustion quality; and
  • The maximum allowable emissions for products of combustion remain the same but are now also keyed to the amount of outdoor air. Lower amounts of outdoor air now mandate more stringent combustion quality.

How The Changes Came About

The new standard came into being as a result of a July 1992 meeting between Canadian and U.S. standards officials. According to Jauch, who is a voting member of the ANSI Heavy Duty Heater Technical Advisory Group (which covers Z83.4 and Z83.18), an ANSI and Canadian Gas Association (CGA) joint subcommittee on standards for gas-fired heavy duty heaters, agreed to prepare a draft of a binational (U.S./Canada) harmonized standard for direct gas-fired industrial air heaters.

“As a part of the revision process, it was decided the two different types of equipment would be covered separately under their own individual standards, Z83.4 for 100% outside air equipment and Z83.18 for recirculated air equipment,” said Jauch. “With the adoption of the new standard for 100% outside air units, Z83.4 (U.S.) and CSA 3.7 (Canada) are now interchangeable (and harmonized) for all listed direct-fired equipment manufacturers.”

It became trickier with Z83.18, because Canada had no comparable standard. “Z83.18 allows recirculation of some room air, however, Canada had never developed a direct-fired standard which allowed recirculation. There was nothing to harmonize,” said Dirkes.

But the U.S. members of the Technical Advisory Group (TAG) felt that there could be some benefits for both countries if a Z83.18 equivalent standard became acceptable to Canada. Most of the two standards are essentially identical, noted Dirkes. The only significant differences are those that deal with recirculation air.

“The Canadian members agreed to consider the possibility of a new Canadian standard, so work was started on a broader revision of Z83.18,” said Dirkes. “But Canada decided to reject a national direct-fired standard which allows recirculation. We think it was due to a combination of historical bias against the idea, plus very aggressive national IAQ standards. I say ‘we think’ because the TAG never did get a very clear answer to inquiries about Canada’s objections.”

The ANSI parent committee approved the new standard, which had been made more robust on a number of fronts, and the TAG decided to propose it as a new U.S.-only standard. Z83.18 was accepted as such in 2000 and, after giving all the manufacturers adequate time to redesign and conduct certification testing, it was made mandatory in January 2003.

Change Can Be Good

So after years of work and not a little controversy, most seem to think the revised standard is just what the industry needs.

Schmidt said it was a good idea, because the units are much safer now. “The revised standard puts a limit on your temperature rise based on the percentage of recirculated air, and that prevents the carbon dioxide concentration from going above 5,000 ppm. Under the old standard, there was nothing to limit that, and units would produce enough carbon dioxide to get a building concentration up above 5,000, which is above the OSHA limitation. The units are now in line with OSHA safety issues.”

Dirkes notes that the previous Z83.18 had an unblemished track record, in his experience, regarding any significant health or safety issues. “On the other hand, the old standard had some gaps in the testing methodology. As IAQ concerns grew larger in the past decade, it made sense to beef up the standard to assure that every possible precaution was taken to create good IAQ in spaces served by this equipment.”

Jauch said that he didn’t think the revisions were completely necessary, but he’s not opposed to them. “The new standard uses a more scientific approach and employs stronger engineering principals for conducting the combustion testing and determining the acceptable levels for emissions. This is good for the direct-fired industry as a whole; the new standard adds credibility and confidence.”

Pirro stated that the new standard adds a greater level of confidence that complying products are operating to provide a higher IAQ.


While everyone may agree that the new standard was needed, some in the industry are confused. The reason for this, said Dirkes, is that the listing/equipment certification process is intended to be simple for those using it: The hard part was supposedly already accomplished by the standards development group (ANSI), manufacturers, and certification agencies (ETL, CSA). “The typical code authority, inspector, or engineer only needs to look for the listing label and make sure it denotes the correct ANSI standard.”

Kaler said he sees one of the biggest problems with engineers. “Most of the specifications we’ve seen from engineers this year and some of the meetings that some of our people have had with code officials in various parts of the country, all of them refer back to the earlier ETL certification.”

This may be happening due to engineering firms’ ubiquitous use of a master specification. As Jauch noted, there is a heavy reliance on master specifications in the consulting and D-B world, and getting the standard specification changed to accurately reflect the requirements of the new Z83.18 standard will take time.

With 30 years of experience in the HVAC industry, Dirkes said he has found very few engineers who understand much at all about the listings they specify. Instead, engineers rely on the “ETL listing” or “UL listing” to be a liability safety net or an insurance policy against assertions that the equipment is unsafe or otherwise inadequate.

“Ask knowledgeable consulting engineers what aspects they like best about a particular ANSI standard that appears in their specification, and you’re almost guaranteed a blank stare,” said Dirkes. “Of course, certain equipment poses less risk than other equipment. Generally, the consulting community appreciates this and is more likely to uphold their specifications when a listing is required for an item that has major health and safety impact. No guarantees, though.” Schmidt said that any specification used by engineers should simply state, “Must be certified to ANSI Z83.18 latest edition.”

“That leaves it open, so when the standards do update, their specifications are automatically updating with them,” Schmidt said.

Kaler said one of his biggest frustrations is that manufacturers have spent hundreds of thousands of dollars for research and development, as well as fees for ETL testing, and nobody seems to know why the units are recertified. “An inspector goes out in the field, and he sees an ETL label unit on a unit that’s certified to the old standard, and he just accepts it.” In the inspecting world, many agree there has been more confusion. ETL decided to interpret the January 2003 compliance date to mean that all products that started manufacturing on or after January 1, 2003 had to comply. This means that some product that shipped in January (but had begun manufacturing earlier) may have been listed to the old standard.


With confusion swirling around about the new and old versions of the standard, some are wondering whether more education is necessary for engineers and building code authorities. Schmidt believes that manufacturers are the ones who need to push the education, since they’re the ones making the equipment that incorporates any changes. He said Greenheck has held several classes for engineers that explain the differences between the new and old versions of the standard. But he also thinks ANSI has some obligation to educate the community.

“ANSI and the manufacturers are the ones I think should be driving the education out there. I think they could do more,” noted Schmidt.

Kaler agrees that something has to change, stating that typically ANSI writes the standards and ETL tests the equipment. This process has meant the HVAC industry remains somewhat self-regulating, with government staying out of the process. “What’s happening this time, though, is that the self-regulating entity, ETL, has no teeth. They can test us and those of us who want to get the most current listing go through the drill, but there’s nobody out there making anybody else do it.”

Then there’s the problem of misinformation being communicated, which further complicates the issue. As Jauch observed, there has been some incorrect information circulated regarding certain types of control systems, which, some have said, do not comply with the emission requirements required by the revised ANSI standards.

One of the primary misunderstandings, according to Jauch, concerns whether or not damper position is an acceptable means for monitoring the amount of outside air being brought in through the unit. The new standard requires the temperature control system to limit the amount of gas consumed based on the amount of fresh air being introduced through the heater (gas consumption corresponds directly with temperature rise). This requires a much more sophisticated control than what may have worked fine in the previous version of the standard.

“Damper position can be used as a repeatable and reliable method, as long as the damper flow characteristics have been calibrated at the factory using an approved method for measuring airflow. The control system has to be programmable and repeatable and require that the damper/airflow calibration be done by a qualified technician. This makes it difficult for any tampering with the device as originally programmed by the equipment manufacturer,” said Jauch. An important lesson to be learned from all this is to stay on top of any changes being made in the industry. Talking with manufacturers’ sales representatives is one of the best ways to find out what’s going on, because you can be sure that when standards change, the manufacturers will be among the first to know.