what is a fvir water heater?

An Innovation in Fire Safety

Prior to 2003 most gas water heaters had an open combustion chamber which allowed the owner to relight the pilot with a match. This presented a danger as hot water heaters in areas where other combustibles such as gasoline or propane caused spontaneous combustion and were a risk to your home and safety.

Residential water heaters manufactured after 2003 are “F.V.I.R.” (Flammable Vapor Ignition Resistant) compliant. For the most part, this means that the combustion chamber is now sealed. In order to light the water heater, you must use the pilot mechanism and you can no longer use a match.

Due to this change, new water heaters are significantly safer than water heaters manufactured before 2003. 

Due to this change, new water heaters are significantly safer than water heaters manufactured before 2003.

Effective July 1, 2003, all water heater manufacturers are required to build their 30,40 & 50 gallon atmospheric vent water heaters to new government standards. The American National Standards Institution (ANSI) have established these new standards to prevent accidental or unintended ignition of flammable vapors, such as those emitted by gasoline.

By July 1, 2005, the ANSI Z21.10.1a-2002 standard will apply to virtually all gas fired residential water heaters with BTU ratings of 75,000 and below.


How do FVIR Water Heaters Work?

All water heater manufacturers came together in cooperation with the Consumer Products Safety Commission to form a Joint Research and Development Consortium. The Consortium agreed upon three basic principles of the F.I.V.R. program:


A one way intake system to control the intake of make up air into the combustion chamber


A flame arrestor plate to provide a one way path for air to travel through


A sealed burner compartment door and assembly to create a sealed junction with the combustion chamber

Air enters through the one way intake system, passes through the flame arrestor plate, and normal combustion occurs in the sealed combustion chamber. In the event that flammable vapors are introduced, the vapors are drawn into the combustion chamber where they ignite in the sealed environment. Due to the flame arrestor plate, the flames are contained within the combustion chamber and cannot escape back out of the heater. Most manufacturers have built in additional features that shut off the flow of gas and seal off the combustion air in the event of a flammable vapor event

What are some of the issues with FVIR water heaters now?

As of writing, it has almost been decades since this technology change.  However, it still creates some confusion.  Specifically, post 2003 manufactured water heaters are all water heaters with enclosed pilot chambers and therefore are “Flammable Vapor Ignition Resistant”.  And as such, due to both the technology and plumbing code – these water heaters no longer need to be elevated 18″ off the floor in a garage.

This often causes confusion with homeowners and sometimes inspectors.  Because non-FVIR pre-2003 water heaters were a substantial fire hazard, it’s become common for people to put their garage water heater on a stand or to elevate it – when it’s no longer necessary or for that matter required by code for current technology.


As a professional installation company that installs a lot of water heaters, this sometimes creates issues.  As water heaters have changed, their size and footprint have also changed; and, there are other important things that have to be addressed when a water heater is properly installed.  For example, on a standard (non direct vent and non power vent) water heater, your flue piping or vent piping should have a positive slope.  This helps CO (carbon monoxide) – a poisonous gas – to properly vent and exit your home.  Due to the changing sizes of tanks, it’s not uncommon for us to have a situation where if we keep a replacement water heater elevated on a stand, the new tank size will result in a negative vent slope. The easy and safe solution, in that case, may be to simply not elevate the tank (which safe with an FVIR compliant water heater).  But, because pre-FVIR tanks were so dangerous, it’s common for some inspectors to enforce old requirements on newer technology.  They are of course doing this to protect the homeowner – so it’s commendable.  It’s just not actually the safest solution in this type of situation.

There are other issues to consider as well – due to changing tank footprints and sizes – sometimes it’s more cost effective for a home owner to install a new tank on a stand and sometimes it’s more cost effective to remove a stand and install a water heater on the garage floor.  (The situation differs home by home and is determined by how much repiping needs to be done, if the stand is in good condition and can be reused and whether or not there is vent/flue work required to make sure the vent is installed and sized properly.)

And, installing a FVIR (post 2003) water heater on a floor is safe.  But, because of how dangerous it was prior to 2003, homeowners, retailers, and inspector sometimes apply the old safety requirements on current technology where it is no longer relevant.  This can be confusing as a home owner can get conflicting information about proper installation.

In most cases, we will install an FVIR water heater on a stand in a garage -because a) it’s more cost effective and b) requires less explanation if someone is applying outdated standards.  But, if there is a good reason – for example installation cost, water heater sizing issues and maintaining positive vent slope being the most prevalent reasons to not elevate the tank – it is a safe and reasonable solution to put an FVIR water heater on the garage floor.

more about fvir water heaters

What was the purpose of switching to FVIR water heaters?

It’s very common for people to have their water heater in a garage.  And, it’s also very common for people to keep gasoline, paint thinner and other flammable items in the garage.  It’s not uncommon for miscellaneous flammables to either spill or in some cases evaporate; when this happens low lying or settled gas could come into contact with the pilot light on a pre-FIVR water heater and cause those materials to ignite.

This was the primary reason that water heaters in a garage where required to be elevated 18″ off the ground (you may notice your garage water heater is on a stand or perhaps elevated in a built in alcove).  Because these gases tend to settle or be on the ground, elevating the water heater prevented fires and explosions by keeping the pilot “out of range” of flammable vapors and gases.

So, why change the water heater if elevating the tank solved the problem?

There are many people who do not have their water heater professionally installed.  And there are many contractors that do not properly permit their work.  So, despite the fact that elevating the tank took care of the issue – many homes still had fire issues due to the water heater being improperly installed and not elevated in a garage.

Enclosing and sealing the ignition chamber solved this issue.

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