BPI Combustion Safety 5

Question 1

What is the role of excess air in combustion, and what happens when excess air is too high?

Accepted Answer

Excess air ensures complete combustion, but too much increases stack losses and reduces efficiency

Answer

Some excess air is needed for complete combustion, but too much carries heat up the flue, lowering steady-state efficiency.

Question 2

In a naturally drafted gas appliance, what causes the 'chimney effect' that moves combustion gases upward?

Accepted Answer

Buoyancy of hot flue gases relative to cooler outdoor air

Answer

Hot flue gases are less dense than cooler outdoor air, so they rise buoyantly up the chimney — this thermal buoyancy is the mechanism of natural draft.

Question 3

What is the minimum recommended CO alarm placement height in a room per most US codes and BPI guidance?

Accepted Answer

At breathing height (5 feet), since CO is the same density as air

Answer

CO has nearly the same molecular weight as air and disperses evenly; most codes specify mounting at breathing height or follow manufacturer instructions, which typically call for a central wall location.

Question 4

A BPI analyst tests a boiler and finds O2 in the flue is 3% and CO2 is 10.5% for natural gas. What does this indicate?

Accepted Answer

Near-stoichiometric combustion with low excess air — efficient but should be verified for CO

Answer

For natural gas, O2 near 3% and CO2 near 10-11% indicates near-stoichiometric combustion with minimal excess air, which is efficient, but CO should be confirmed low.

Question 5

What action should a BPI analyst take if an atmospheric water heater fails to draft during worst-case depressurization testing?

Accepted Answer

Document the spillage, classify the appliance as a safety hazard, and recommend correction before weatherization proceeds

Answer

Failed draft under worst-case conditions is a confirmed combustion safety hazard; BPI requires documenting it and flagging it as a priority safety issue before any weatherization work.

(BPI) Building Performance Institute Certified Practice Test

(BPI) Building Performance Institute Certified Practice Test

BPI Combustion Safety 5