Robert Naini, your Spray Foam Advisor, talks about combustion appliances, pressurization dynamics and safety of combustion appliance zones.
Hey, this is Robert Naini, your Spray Foam Advisor and today I want to talk about combustion appliances.
Now we work in all types of structures and all types of buildings.
But do you know when there are combustion appliances on the properties that you are working on?
It is very important that you do.
Because spray foam changes the way the buildings work, fundamentally at an air leakage level.
Of course, spray foam provides insulation value but the biggest advantage of spray foam over other insulation materials is that spray foam insulation is also an air barrier on the same plane as the insulation in a single application.
By providing this air barrier with spray foam insulation, we are changing the pressure dynamics of the structure, this changes the way air moves in, out and around the building.
So, it is critically important that we know when there are combustion appliances present in the buildings that we insulate, where they are located, where the combustion air is coming from and where the appliance exhaust is discharged.
These concepts are all important and they are directly related to combustion appliance zone safety or CAZ safety.
When you have a gas combustion appliance, like a water heater, stove or furnace, they require air as part of the combustion process.
When the combustion appliance draws in air for the combustion process, it creates a negative pressure in the surrounding area, so make up air should be supplied to the appliance or the surrounding area, typically from the outside of the structure.
Also, the combustion process produces CO2 and moisture, both of which are indoor contaminants, so they must be exhausted to the outside of the building enclosure.
So, if you are changing the building enclosure, such as adding spray foam insulation in a residential retrofit, it is critically important that you pay attention to CAZ safety.
Everyone involved in the project, you, the owner, the general contractor, and everyone else involved in the project, should have a discussion about combustion appliance zone awareness, to discuss how tightening the envelope might affect any combustion appliances on the premises.
Let’s look at an example:
We have a traditional attic with a gas combustion water heater in this space.
You are asked to come into this project and create a closed, unvented attic using spray foam insulation in this retrofit project.
What happens next?
To properly create the unvented attic assembly, you need to install the spray foam insulation, which is an air barrier, directly to the underside of the roof deck, eliminating all attic ventilation, which puts the attic space inside the building enclosure.
Now, the attic is a combustion appliance zone and some safety precautions are required.
We need to verify two things:
- Make-up combustion air is being brought in from the outside
- The exhaust fumes are being properly vented outside the building enclosure and are not back drafting into the structure
So how does this work today.
The newer, high-efficiency combustion appliances are typically sealed combustion systems.
With sealed combustion systems, everything is maintained in a closed loop environment, so make-up combustion air is not drawn from the surrounding area, rather, this system uses a double-walled pipe.
The make-up air and the exhaust air run through the same pipe, separated by an interior wall system, or a pipe within a pipe.
However, lower-efficiency appliances are often open combustion systems, which means they draw their combustion air from the space around them.
This could mean that a mechanical space or mechanical room may need to be constructed around an open combustion appliance to make sure the combustion appliance zone can be properly managed with make-up air being brought in from the outside and exhaust fumes being directed outside the building enclosure.
In the end, make sure that you are aware of the combustion appliances on any project that you are working on and know how what you are doing to the building will change the way the building works and affect any combustion appliances and combustion appliance zones on your project.
This has been Robert Naini, your Spray Foam Advisor, thanks for checking me out and catch me on some more videos.
