Combustion Closet Rules for Rental License Inspections

Date Published: October 27, 2022

Furnaces and water heaters are key elements in any Colorado home. However, being that they are combustion appliances, they can pose safety and health hazards if not configured properly. One of the most common practices in the residential setting is to have these appliances installed in a combustion closet.

When it comes to Denver and Boulder rental properties, there are strict guidelines with regards to combustion closets or rooms. For rental license inspections, it all boils down to safety. A rental property needs to meet a list of standards in order to be deemed safe for its occupants.

new furnace and water heater

Furnace with direct ventilation and water heater. Image sourced from:

Why Are Proper Combustion Closets So Important?

Combustion appliances are, by definition, fuel-burning. They combine a gas supply with oxygen in order to create fire. This reaction, in turn, heats your water and air.

The byproducts of this chemical reaction are carbon dioxide and water. In many cases, if the fire is not receiving enough oxygen, it will produce carbon monoxide, instead of carbon dioxide.

Carbon monoxide (CO) is highly toxic to humans if not ventilated properly. So, it follows that an enclosure with a combustion appliance must be built properly to ensure safe living conditions.

A fuel-burning device needs a source of fresh combustion air and an avenue for ventilation to expel its fumes. If the device does not have unhindered access to fresh air, it may begin to create negative pressure and pull the air it needs through the exhaust piping. Once that air is moving inward through the exhaust pipe, the fumes being produced as a byproduct have nowhere to go but back into the home. Now we have CO making its way into the living space, and that is an obvious problem.

It was common practice in many older homes to put combustion appliances in closets with louvered doors (shown below). The slats in these doors allow the appliance to draw fresh air in from the interior of the home. And if the ventilation flue is installed properly with no obstructions, this configuration should technically work.

gas furnace and water heater in combustion closet with louvered door

Furnace and water heater combo in closet with louvered door. Image sourced from:

However, according to code, using the louvered door method can be hazardous and especially unacceptable in certain locations such as the bedroom or bathroom.

For instance, if a fire were to break out in a bedroom combustion closet, without the proper fire-proofing precautions (i.e. a louvered door), the fire could quickly spread into the bedroom. Or what if a combustion device is located in bathroom closet with a louvered door? If someone turns on the exhaust fan, it could potentially create a backdraft and start to pull CO fumes into the bathroom.

Due to all these potential issues, it eventually became apparent that we needed to establish a standard for combustion appliances and how they are installed in the home.

Combustion Closets, By The Book

As mentioned above, when conducting rental license inspections in Boulder and Denver, inspectors are going to be paying close attention to the location and configuration of furnaces and water heaters. Both municipalities have similar standards. They have adopted the codes established in section 303.3 of the 2021 International Fuel Gas Code (IFGC).

So, can furnaces and/or water heaters be located directly inside bedrooms or bathrooms? No. However, they can be accessible through bedrooms or bathrooms, as long as they are contained in an isolated room or closet.

If a fuel-burning appliance is accessed through a bedroom or bathroom, it must be installed in a room or closet that is completely sealed with weather stripping and a door equipped with a self-closing device. Additionally, the appliance must have its own access to a source of combustion air from the outdoors. Furthermore, its exhaust must also terminate outside the home through its own dedicated piping. When built correctly, these combustion closets should have an airflow system that is operating independently of the living space.

The diagram below illustrates a water heater in one of the most efficient types of sealed combustion closets. Most new furnaces are built with direct ventilation systems (top picture shown above), meaning their intake and exhaust piping are mounted directly onto the appliance. These examples illustrates two different methods for proper combustion appliance configuration.

combustion closet

Properly configured combustion closet. Image soured from:

Utility rooms are commonly located in basements, and there are many basement rental units. It follows that the rental license guidebooks also address these specific living spaces. Any habitable part of the basement unit must be separated from any room containing fuel-burning appliances. According to section 4.2 of Denver’s residential rental program guidebook:

“If a fuel-fired furnace is located in a room that opens directly into an area used for sleeping, the two rooms must be separated by a solid core 1-hour fire-rated door with a smoke seal around it.”

Rental License Inspections

At Scott Home Inspection, we have been offering our rental license inspection services to the Boulder area for 10+ years. And now with the recently implemented Denver residential rental license requirements, we have several certified inspectors who are qualified to offer the same, high quality rental inspection services to the city of Denver.

Home Inspector inspecting furnace

When observing the combustion appliances in the home, our inspectors will consider a few key questions. Is the appliance functioning properly? Is it installed in a safe, and code-acceptable location? Does it have proper ventilation? Does it have an adequate combustion air supply? Any deficiencies noted at the time of inspection will be called out for repair and/or correction.

Our number one priority is to help Colorado families live in safe, healthy, and comfortable homes. So when assessing a rental property for licensing, our inspectors are as thorough as possible. We observe all aspects of the property as required by the municipality, and provide an unbiased pass or fail assessment.

If you are in need of a rental license, we recommend reviewing the applicable rental license guidebooks (City of Denver or City of Boulder) prior to the inspection.

We hope you will contact Scott Rental Inspections for your next Colorado rental license inspection! For more info, feel free to contact us today!

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About the Author: Chris Kimmel

Chris Kimmel worked as an Associate Home Inspector for two years, handling numerous services including sewer scope inspections, pest inspections, mold air sample testing, radon testing, and water quality testing. Chris now works with Scott Home Inspection as a Content Writing Specialist.

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