I was recently contacted by a friend who wants to install a kitchen exhaust range hood to a 100-year-old house. They were looking for insight on how the fan could be added, where the ducts could be located, sizing of the system, and any other considerations to be aware of.

A critical question that needs answering before adding any type of new exhaust system is why? In the case of this house, existing equipment included a vented, natural gas boiler and water heater. This type of equipment has the potential to “spill” or backdraft combustion exhaust if a house becomes negatively pressurized.

How do you know if the equipment is drafting correctly? How do you know if there is carbon monoxide or combustible gas present? What happens if a new exhaust fan is added?

As always, start by testing

To answer these questions, we test! This includes combustion appliance zone (CAZ) testing, monitoring ambient and flue CO levels, and a blower door test.

Both the Building Performance Institute (BPI) and the Residential Energy Network (RESNET) have outlined how to perform CAZ and blower door testing. This article will follow the standards of ANSI/BPI 1200, Standard Practices for Basic Analysis of Buildings; the RESNET standards are similar.

[My wearable CO/LEL monitor, gas leak detector, and combustion analyzer]

The process starts with calibrating the monitoring and testing equipment in fresh air, outdoors. The four types of equipment that require fresh-air calibration are CO monitors, explosive gas monitors (lower explosive limit or LEL monitors), combustible gas leak detectors, and combustion gas analyzers. (My wearable CO monitor measures both CO and LEL). For my initial trip into a house, the CO/LEL detector is clipped to my clothing.

Investigation and safety check

After questioning the homeowner for relevant information, I perform a visual…