HERS Combustion Safety Questions and Answers 1 — Questions and Answers
Question 1: A HERS Rater is performing a worst-case depressurization test in a home with a natural draft gas furnace and a gas water heater sharing a common masonry chimney. The rater first tests the water heater, which fails the spillage test, continuing to spill for more than 60 seconds. What is the appropriate next step?
- Immediately red-tag the appliance and recommend replacement.
- Proceed to test the furnace under worst-case conditions to see if it also fails.
- Stop the worst-case test, return the house to natural conditions, and re-test the water heater for spillage. (Correct answer)
- Advise the homeowner to have an HVAC technician clean the chimney before any further testing.
Correct answer: Stop the worst-case test, return the house to natural conditions, and re-test the water heater for spillage.
According to RESNET and BPI procedures, if an appliance fails a spillage test under worst-case depressurization, the next step is to test it under natural conditions. This helps determine if the problem is caused by building depressurization or an issue with the appliance/venting system itself. If it passes under natural conditions, the problem is likely related to house depressurization. If it still fails, the appliance/vent system requires service by a qualified technician.
Question 2: During combustion safety testing, a rater's personal CO monitor alarms, indicating an ambient carbon monoxide level of 40 ppm in the Combustion Appliance Zone (CAZ). What is the immediate required action?
- Continue testing but note the high ambient CO level in the report.
- Stop testing, turn off the combustion appliances, ventilate the area, and evacuate the space. (Correct answer)
- Put on a respirator and complete the testing protocol as quickly as possible.
- Zero the combustion analyzer in the CAZ and proceed to measure the undiluted flue gases.
Correct answer: Stop testing, turn off the combustion appliances, ventilate the area, and evacuate the space.
Safety protocols from RESNET, BPI, and DOE require that if ambient CO levels in the CAZ exceed 35 ppm, the rater must stop all testing immediately, turn off the appliances, open windows and doors to ventilate the space, and leave the area. This is a critical safety measure to protect both the rater and the occupants from CO poisoning.
Question 3: Which of the following sets of actions is required to establish the 'worst-case' depressurization condition in a Combustion Appliance Zone (CAZ) before testing appliances?
- Opening all exterior windows, closing all interior doors, and turning on the furnace fan.
- Turning on all kitchen and bath exhaust fans, starting the clothes dryer, and closing doors to rooms that make the CAZ pressure more negative. (Correct answer)
- Operating the whole-house ventilation system at its highest setting while opening the door to the CAZ.
- Turning on the air handler, closing all supply registers, and opening all return grilles.
Correct answer: Turning on all kitchen and bath exhaust fans, starting the clothes dryer, and closing doors to rooms that make the CAZ pressure more negative.
Creating the worst-case depressurization scenario involves operating all devices that exhaust air from the building simultaneously. This typically includes kitchen exhaust fans, bathroom fans, and the clothes dryer. Additionally, interior doors are strategically opened or closed to maximize the negative pressure in the CAZ relative to the outdoors; doors to rooms that become pressurized are closed, while doors to rooms that become depressurized are opened.
Question 4: A HERS Rater is inspecting a newly installed high-efficiency condensing furnace that is a direct-vent, sealed-combustion unit. The intake and exhaust pipes are routed directly to the outdoors. Which combustion safety test is NOT required for this type of appliance?
- A gas leak check at the pipe fittings near the unit.
- A measurement of carbon monoxide (CO) in the flue gas.
- A visual inspection of the vent terminations for proper clearance.
- A worst-case depressurization and spillage test. (Correct answer)
Correct answer: A worst-case depressurization and spillage test.
Direct-vent, sealed-combustion appliances draw all of their combustion air directly from the outdoors and have a sealed exhaust system. Because they do not communicate with the indoor air, they are not susceptible to depressurization-induced backdrafting or spillage. Therefore, a worst-case depressurization test is not applicable to these units. However, CO testing, gas leak checks, and visual inspection of the system are still important safety checks.
Question 5: When performing a draft test on a natural draft furnace, the primary purpose is to verify that:
- The heat exchanger has reached its steady-state efficiency.
- The flue gas temperature is within the manufacturer's specified range.
- A stable, negative pressure is established to continuously move combustion byproducts up the flue. (Correct answer)
- The ambient air in the CAZ has sufficient oxygen for complete combustion.
Correct answer: A stable, negative pressure is established to continuously move combustion byproducts up the flue.
The purpose of a draft test is to confirm that the venting system is creating a sufficient and sustained negative pressure (draft) to pull the flue gases out of the appliance and exhaust them safely to the outdoors. An inadequate or unstable draft can lead to spillage of combustion byproducts into the home. While related to temperature and efficiency, the direct purpose of the draft measurement itself is to verify this negative pressure.
Question 6: During a visual inspection of a natural draft gas furnace installation, which of the following conditions found on the metal flue vent connector is an immediate safety concern that must be noted for correction?
- The vent connector has a total of two 90-degree elbows.
- The vent connector is single-wall galvanized steel.
- The vent connector slopes downward from the appliance to the chimney. (Correct answer)
- The vent connector is secured at each joint with three sheet metal screws.
Correct answer: The vent connector slopes downward from the appliance to the chimney.
Flue vent connectors for natural draft appliances must have a continuous upward slope from the appliance to the chimney, typically a minimum of 1/4 inch per foot of horizontal run. A downward or level slope can trap flue gases, prevent proper drafting, and lead to condensation, corrosion, and spillage of carbon monoxide into the home. This is a significant safety hazard.
HERS Combustion Safety Questions and Answers 1
A HERS Rater is performing a worst-case depressurization test in a home with a natural draft gas furnace and a gas water heater sharing a common masonry chimney.
The rater first tests the water heater, which fails the spillage test, continuing to spill for more than 60 seconds.
What is the appropriate next step?