Weatherization Manual Policies and Procedures Supporting Documents for United States Department of Energy (doe) United States Department of Health and Human Services (hhs) Bonneville Power Administration

State of Washington, Weatherization Assistance Program

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State of Washington, Weatherization Assistance Program

Technical Support Document

Combustion Safety

This document is intended to support in detail the Combustion Safety Test Report. The Combustion Safety Test Report is a tool to document the condition of two (2) appliances and their performance. Each combustion appliance in homes that are weatherized or repaired must be reported pre- and post- on a combustion safety test report. The added columns allow two (2) combustion appliances per form. Each row of the pre- and post- columns must be addressed.

The Combustion Safety Test Report must be filled out in detail for each completed project. You must document in the comments section of the Combustion Safety Test Report any special circumstances or health and safety related concerns that might help someone understand the condition of the home (pre- and post-), as well as the concerns expressed by the occupants, or the agency concerns for the occupants safety at the time testing was performed.

The testing procedure outlined in this document is intended to be the minimum tests needed to understand the condition and performance of an appliance. It is recommended that more in-depth testing be performed where multiple appliances share a chimney, or where other indications of potential problems exist.


Start CO measurement (Monoxer) outside.

Line #1 Measure existing Combustion Appliance Zone (CAZ) pressure (baseline), CAZ With Respect To (WRT)) outside.

Measure the existing CAZ pressure (baseline), house with reference to outside. You will need this measurement when measuring combustion appliance zone worse case and other procedures that are normally low-pressure measurements (-15pa to 15pa).

Line #2 Outdoor wind speed

Using a Dwyer wind gauge, measure and record the outside wind speed if there is noticeable wind at the time of testing. If the wind speed is consistently in excess of 15 mph or gusting to the point of not being able to get an accurate test, document this condition and return at a later date to get accurate test results. If winds in excess of 15 mph do exist, this condition does not preclude performing Section I and Section II of the diagnostic test report. Under these conditions you will have to come back (when there is wind less than 15 mph) to confirm lines #8, 13, 15 and 17. You may find hazardous conditions before you get to line #8, or other problems not related to pressure and draft.

Line #3 Outdoor temperature

Record the outside ambient temperature. You will need this number to determine if there is adequate minimum draft (line #13 &15).

Line #4 Combustion Appliance Zone(CAZ)*, designate appliance

Record what kind of appliance (furnace, hot water heater, parlor stove, fireplace, woodstove, etc.) is in the CAZ. Write it in on the line provided. Also determine what type of appliance it is in terms of direct vent, sealed combustion, induced draft, etc. This will help determine how and where an appliance should be tested later in this procedure.

*Definition: Combustion appliance zone (CAZ) is the physical area in which the combustion appliance is located or contained by door or access closure. Examples: A closet with a closing door, an attic with a closing access panel between the living space and attic, a living room that contains a fireplace or wood stove and has doors that isolate this area from bedrooms and other rooms. A combustion appliance zone is any area (zone) which can be physically closed off to another part of the home, and that contains a combustion appliance. If the only combustion source is a fireplace or wood stove go to line #17.

Line #5 Is there a hazardous or unsafe condition?

Is there anything in the CAZ that could be considered a health and safety problem? Indoor Air Quality (IAQ), electrical discrepancies, fire hazards, combustibles, or potential testing problems that should be documented. If yes, you must comment with name and date.

Line #6 Are there visible signs of vent pipe leaks or damage?

Are there any problems with the combustion appliance vent pipe, connecting chimney, chimney liner, or vent termination that need repairs or further inspection?

Line #7 Is there the smell of gas or indication of fuel leak

Do you or the client smell any gas? Did you check with a combustible gas detector or with detection fluid? If there is a leak, indicate by marking yes, and contact the local natural gas company or a contractor and document the location of the leak below in the comments section .

Worst-case* set-up test for Combustion Appliance Zone.

*Definition: Worst-case is any condition that puts the appliance being tested in the most hazardous condition through means of house configuration. These configurations such as opening and shutting bedroom, laundry, garage, closet, basement, doors, etc., may occur during normal use of the home. This may be different for different lifestyles and occupants, but the CAZ should be tested in a manner that would address many clients and lifestyles. All reasonable house configurations should be considered.

Worst-Case Set-Up procedure

Prepare house:

  1. Close all interior and exterior doors and windows. Is furnace air handler on or off? Could be worst case either way, depending on duct leakage. Turn on all exhaust fans - bathroom, kitchen, clothes dryers (clean out lint filter).*

  2. Start at the room furthest from the combustion appliance and perform a smoke test at each interior door to determine whether to leave it open or closed.

    1. Position yourself in or towards the main body of the house.

    2. Open the door slightly (3/4”). If the smoke goes in, leave the door all the way open. If the smoke comes back toward the main body or towards you, close the door.

  3. Smoke test the door to the CAZ. If the smoke comes toward the main body or towards you, open the door. If the smoke goes into the CAZ, close the door.

* EXCEPTION TO STEP (1.) If the furnace does not have a manual fan switch you may have to turn on all your fans first (smoke the doors) then turn on the furnace. In this case you must do line #13 a second time, going back and smoking the interior doors again to ensure you had the correct setup. If this is the case, and you go back and find that you had a door in the incorrect position (opened or closed), adjust, retest, document the results, and go back through lines #8 through #13.

Always check rooms that contain mechanical exhaust equipment with chemical smoke as a confirming test. Many times the combination of leaky buildings and supply ducts in a room negate a fans negative effect on the CAZ or main body.

Line #8 Measure the CAZ WRT outdoors. Is the CAZ door Open or closed?

Follow worst-case set -up procedure (above) to determine whether to leave open or shut the CAZ room door(s). Please circle whether you left the CAZ door OPEN or CLOSED. Then record what the pressure is in the CAZ WRT outside using line #1, CAZ baseline pressure to have a better understanding of the contribution the mechanical systems are having on the home versus natural pressures (i.e. stack wind etc.).

**Action Level

Table 4: CAZ Depressurization Limits

Line #9 Was there flame roll-out of combustion equipment?

When the (furnace or hot water heater) combustion appliance starts up, does the flame come out of the appliance? When possible, this test should be done with a cold startup. Many times if the chimney or vent pipe is already heated, the appliance will draft, but it may not be able to start a draft in a cold chimney. Also, check cover panels and the area around the burner for burned or charred spots. If you see flame roll out or signs that it may be happening intermittently then circle YES and comment in file.

Line #10 Did the equipment spill gases for more than one minute?

Does the atmospheric draft or induced draft (hot water heater, parlor stove, furnace etc.) appliance spill combustion gases for more than a minute? If YES, STOP test. Let cool. Continue test in natural conditions. Check all around the draft hood with chemical smoke, as some appliances will spill combustion gases and draft at the same time.

Table 2: Maximum Acceptable Appliance Spillage Periods

Appliance Type

Spillage Test Period (minutes)

Water Heater, Gravity Furnace, Boiler


Space Heater


Forced Air Furnace


** Note: Generally you will find that if an appliance spills combustion gases for more than one (1) minute, this is an indicator that there will be a draft, chimney configuration, or pressure problems detected at some point between lines 13 and 16.

Line #11 Did the flame change in the furnace when the air handler turned on?

Did the flame change when the fan in the furnace turned on? This can indicate a crack in the heat exchanger. If yes, comment in the file and have it checked by HVAC technician.

** Note: If you are working on a furnace without a manual fan switch, you may have to shut down the furnace and start it again to observe this condition because you will have a lot going on when the air handler comes on the first time. Checking for flame change may not detect an existing cracked heat exchanger. Other possible indications of a cracked heat exchanger may be soot in the home, the smell of un-burnt gas or oil, elevated CO levels in the appliance exhaust, and elevated CO levels in the living space when the furnace is running. If you encounter any of these conditions, there are other tests for cracked heat exchangers that you may want to identify and have performed by a qualified professional (check with your HVAC contractor or technician). Caution and a full understanding of the operating performance of all the combustion appliances in the home must be considered when attributing soot, un-burnt gas smells, and elevated CO levels to a cracked heat exchanger.

Line #12 After 5 minutes measure the CO in the ambient air in the living space

Zero the monoxer outside before proceeding. After the combustion appliance has been running for 5 minutes, test the ambient air of the living room or upstairs hallway (if it is a two story) for CO with your monoxer. Record any CO in the living space above zero (0) in parts per million (PPM).

**Action level: If the ambient CO in the home is above 9 PPM (maximum allowable 9 PPM) and attributable to any combustion appliance in the home, then action must be taken to mitigate the source of the CO before weatherization or repair work starts, or the ambient CO level must be monitored and the problem(s) resolved as part of the work specified. No home shall be left with ambient CO greater than 9 PPM (attributable to existing combustion appliances) after 5 minutes of run time for an appliance.

Line #13 Measure the draft pressure in the vent of the combustion appliance Test the combustion appliance vent WRT CAZ

With your digital manometer, measure the draft pressure in the combustion appliance vent (preferably 18” up the vent pipe from the appliance) with reference to the room and record the number in pascals. Be sure to indicate whether negative or positive. Always check your draft pressure measurements with chemical smoke as a confirming test.

If the appliance does not have adequate draft under worst-case conditions, you can start evaluating the problem by turning off all fans and see if the appliance drafts under any or best case condition.

Refer back to line# 2 and check the wind speed, if the wind speed is consistently in excess of 15 mph or gusting to the point of not being able to get an accurate test, document this condition and return at a later date to get accurate test results. If there is marginal draft or a condition that may cause back drafting or spillage, inform the occupants of this situation and make the appropriate recommendations for use of the appliance until additional testing or repairs can be made. Document the condition in the comments section.

Line #13a Minimum Acceptable Draft Pressure: Calculate the minimum acceptable draft pressure using the ranges in Table 1 and record limit in the box.

Table 1: Minimum Acceptable Draft Test Action Levels

Outside Temperature (degree F)

Draft Pressure Standard (Pa)




(Outside temp / 40) – 2.75*



*Calculation is as follows: Divide the outside temp by 40, then subtract 2.75 from this value. The result is the minimum acceptable draft.

Line #14 Measure the CO in the exhaust gases of the vented appliance

With your monoxer, take a measurement in the undiluted flue gases of the combustion appliance. Where practical, this test should be measured in the flue ports of the appliance. If you cannot measure at the appliance, measure at its termination point realizing this is a diluted sample but better than not testing at all.

Table 3: Combustion Safety Test Action Level Table

Line #15 If the door of CAZ is closed - open it. If the door is open – close it. Open/closed. Combustion Appliance vent WRT CAZ.

If in the beginning of your worst-case set-up test, you left the CAZ door closed, then open it. If left open in the beginning, then close it. Then record the draft pressure combustion appliance vent WRT CAZ as in line #13. This is a verifying test. This test double checks your measurements and helps confirm the results. Always check your draft pressure measurements with chemical smoke as a confirming test.

**Action Level: See action level Table 4 - CAZ Depressurization Limits

Line #16 Heat Rises: Measure temperature across heat exchanger:

Heat rise = supply plenum temp - return plenum temp

To get the “heat rise”, measure the temperature in the supply air plenum and return air plenum. Subtracting the return plenum temperature from the supply air temperature equals the “heat rise”. Take these temperature measurements in the plenums as close to the furnace as possible. Record in degrees Fahrenheit. The manufacturer’s acceptable range for heat rise for the unit is often on the nameplate of the furnace.

**Action level: If the heat rise (the difference between return air temp at the plenum and supply air temp at the plenum) is outside the manufacturer’s acceptable range the system fails and there must be a referral made for further analysis by a furnace technician. If the heating unit has not been serviced within the last twelve months, a furnace clean and tune is recommended.

Exception: If manufacturer’s acceptable heat rise range is unavailable, the default acceptable heat rise range is greater than 40° and less than 70° Fahrenheit.

Line #17 Fireplace/wood stove zone worst case test: FPWSZ zone WRT outdoors

Record the pressure of the zone that the fireplace or wood stove occupies. See Worst-Case Set-Up Procedure between lines #7 and #8, this procedure is the same for fireplace/wood-stove zones. Also document any vent pipe, chimney, or clearance problems with the wood-burning appliance in the comments section.

**Action Level: See action level Table 4 - CAZ Depressurization Limits on reverse side of Combustion Safety Test Report (Exhibit 5.3.1A)

Line #18 Measure the CO in exhaust gases of Ovens:

Interim Gas/Propane Oven Testing Procedure

Ovens produce moisture and oxides of nitrogen. Excess moisture is not good for the durability of the home (possibly contributing to mold problems) and NOX is not healthy. These combustion appliances are capable of producing CO, which is a health hazard. In all cases a carbon monoxide detector is recommended and homeowners should use exhaust ventilation when using these appliances. New appliances may require an extended warm up period to reach steady state.

    1. Remove any items/foil in or on oven.

    2. Make sure self cleaning features are not activated, set oven to highest setting.

    3. Test oven for CO in the flue, before dilution air.

    4. After 5 minutes of operation, check for steady state:

If the appliance is located in a confined space and mechanical ventilation is not readily available, mechanical ventilation shall be recommended.

Ventilation provided for unvented gas ovens must provide a minimum capacity of 25 cfm continuous airflow or 100 cfm intermittent.

Then take a reading in the undiluted flue gases of the oven (after 5 minutes of burn time) and record in PPM. Look in the oven for anything that may melt or catch fire before performing the test. Make sure the oven burner is actually on during the test.

Ambient CO Levels

Carbon monoxide levels in the ambient air around the technician must be monitored throughout all combustion safety tests. Diagnostic evaluations and inspections must be aborted if ambient CO concentrations greater than 35 ppm are recorded. CO producing appliances must be disabled and repaired before proceeding with additional diagnostics or inspections.

Ambient CO levels shall be monitored upon entering the combustion appliance zone and during the test period for all appliances. If ambient levels exceed 35 ppm at any time, turn off the appliance immediately and make appropriate repair recommendations according to the charts provided.

**Action Level: See action level

Table 3.1 - Carbon Monoxide Test Action Levels for Ovens

Line #19 Return house to pre-test condition, circle DONE when complete

Comments: Provide comments in detail when you encounter unsafe conditions. Also document procedures or repairs that were undertaken to resolve or prevent any unsafe conditions. Use both sides of the form or additional paper as needed.


CO: Carbon monoxide

CA: Combustion appliance

CAZ: Combustion appliance zone

FPWSZ: Fireplace wood stove zone

HDL: House Depressurization Limit (a standard adopted by Commerce)

HVAC: Heating, ventilation, air conditioning

IAQ: Indoor Air Quality

PPM: Parts per million

Pa: Pascals

WRT: With reference to


Air handler – A steel cabinet containing a blower with cooling and/or heating coils connected to ducts, which transport indoor air to and from the air handler.

Backdrafting – Continuous spillage of combustion gases from a combustion appliance.

Bimetal element – A metal spring, lever, or disc made of two dissimilar metals that expand and contract at different rates as the temperature around them changes. This movement operates a switch in the control circuit of a heating or cooling device.

Burner – A device that facilitates the burning of a fossil fuel like gas or oil.

Carbon monoxide – An odorless and poisonous gas produced by incomplete combustion.

Combustion air – Air that chemically combines with a fuel during combustion to produce heat and flue gases, mainly carbon dioxide and water vapor.

Combustion analyzer – A device used to measure steady-state efficiency of combustion heating units.

Depressurize – Cause to have a lower pressure or vacuum with respect to a reference of a higher pressure.

Dilution air – Air that enters through the dilution device --- an opening where the chimney joins to an atmospheric-draft combustion appliance.

Dilution device – A draft diverter or barometric draft control on an atmospheric-draft combustion appliance.

Draft diverter – A device located in gas appliance chimneys that moderates draft and diverts down drafts that could extinguish the pilot or interfere with combustion.

Fan control – A bimetal thermostat that turns the furnace blower on and off as it senses the presence of heat.

Flue – a channel for combustion gases.

Heat anticipator – A very small electric heater in a thermostat that causes the thermostat to turn off before room temperature reaches the thermostat setting, so that the house does not overheat from heat remaining in the furnace and ducts after the burner shuts off.

Heat rise – The number of degrees of temperature increase that air is heated as it is blown over the heat exchanger. Heat rise equals supply temperature minus return temperature.

High limit – A bimetal thermostat that turns the heating element of a furnace off if it senses a dangerously high temperature.

House pressure – The difference in pressure between the indoors and outdoors measured by a manometer.

Inch of water – Small air pressure differences caused by wind, blower doors, furnace fans, and chimneys are measured in inches of water (in.-H20) in the American measurement system.

Input rating – The rate at which an energy-using device consumes electricity or fossil fuel.

Intermittent ignition device – A device that lights the pilot light on a gas appliance when the control system calls for heat thus saving the energy wasted by a standing pilot.

Make-up air – Air supplied to a space to replace exhausted air.

Manometer –Measuring device for small gas pressures

Mortar – A mixture of sand, water, and cement used to bond bricks, stones, or blocks together.

Net free area – The area of a vent after that area has been adjusted for insect screen, louvers, and weather coverings. The free area is always less than the actual area.

Open-combustion heater – A heating device that takes its combustion air from the surrounding room air.

Orphaned Natural Draft Water Heater - A natural draft water heater vented into an oversized chimney.

Oxygen depletion sensor (ODS) – A safety device for unvented combustion heaters that shuts gas off when oxygen is depleted.

Pascal – A unit of measurement of air pressure. (See Inch of water.)

Plenum – The piece of ductwork that connects the air handler to the main supply duct.

Pressure – A force encouraging movement by virtue of a difference in some condition between two areas.

Return air – Air circulating back to the furnace from the house, to be heated by the furnace and supplied to the rooms.

Room heater – A heater located within a room and used to heat that room.

Sealed-combustion heater – A heater that draws combustion air from outdoors and has a sealed exhaust system.

Space heating – Heating the living spaces of the home with a room heater or central heating system.

Spillage – Temporary flow of combustion gases from a dilution device.

Stack effect – The draft established in a building from air infiltrating low and exfiltrating high.

Stand-Alone Natural Draft Water Heater - A natural draft water heater vented into a properly-sized chimney in accordance with NFPA 31 for oil-fired units, NFPA 54 for gas-fired units, NFPA 58 for propane-fired units and NFPA 211 for solid-fueled units or the venting tables of a chimney liner manufacturer.

Steady-state efficiency – The efficiency of a heating appliance, after an initial start-up period, that measures how much heat crosses the heat exchanger. A combustion analyzer measures the steady-state efficiency.

Supply air – Air that has been heated or cooled and is then moved through the ducts and out the supply registers of a home.

Vent connector – The vent pipe carrying combustion gases from the appliance to the chimney.

Vent damper – An automatic damper powered by heat or electricity that closes the chimney while a heating device is off.

Venting – The removal of combustion gases by a chimney.

Worst-case depressurization test –A safety test, performed by specific procedures, designed to assess the probability of chimney back drafting.

WRT – “With respect to” used to show that the air pressures between two areas are being compared.

Zone – A room or portion of a building separated from other rooms by an air barrier----not usually an effective air barrier.

Floor Support Matrix


Floor Type

Support Material

Material requirements

Maximum Spacing

Acceptable patterns

Minimum fastener type

Minimum fastener depth

Joist up to 24"




Across floor joists

Corrosion resistant 3/8"crown 18AWG


Joist up to 24"


150 LBS. polyester, polypropylene or nylon

12" O.C.

Shoelace/Zigzag (must be stapled at each joist

Corrosion resistant 3/8"crown 18AWG


Post &Beam over 32" O.C.



20" O.C.

Across floor beams up to 54". If over 54" need center support

Corrosion resistant 3/8"crown 18AWG


Post &Beam over 32" O.C


150 LBS. polyester, polypropylene or nylon


Shoelace up to 54" across. If over 54" need center support

Corrosion resistant 3/8"crown 18AWG


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