Performing a Draft Test

Performing a Draft Test:

Verifying draft and checking for spillage is an important safety consideration. Draft is required to remove the flue gasses from the heat exchanger or draft hood on all atmospheric and draft induced appliances, and most power burner equipped appliances.
 
All appliances requiring draft are required to have and maintain draft during operation.  
 
 An appliance has 5 minutes under the ANSI standards to prove draft. 
 
If following BPI standards, Vented appliances, regardless of type, that spill flue gases for more than 60 seconds after startup, fail the spillage test.  
 
During steady state operating conditions, the draft should be stable. The draft will increase as the flue warms until it reaches maximum flue temperature and stabilizes.  The analyzer will record and store the draft reading for the flue gas measurement screen and printout.
 

 

Note: If the appliance and chimney are cold it can take up to five (5) minutes to establish draft. (a spill switch must trip within ten (10) minutes if spillage occurs. A system that has been under operation should have or establish draft very quickly. If draft induced and atmospheric appliances are common vented, always verify the atmospheric appliance is not spilling when both appliances are operating.  Verify that flue gasses are not spilling through the draft hood on the atmospheric appliance when it is operating by itself. If both appliances are common vented, both should be draft tested. Kitchen exhaust fans, basement doors opening or closing etc, should not affect draft. If multiple draft-induced appliances are common vented, assure that spillage does not occur through the heat exchanger and out through the burner openings of the adjoining appliance while it is in its stand-by position (OFF)

 

Spillage and Draft Tests

Spillage and draft tests must be completed for all natural and induced draft space heating systems and water heaters. Spillage and draft must first be tested under worst-case conditions and then repeated for natural conditions if the appliance fails under worst-case.

 

When a chimney is shared by multiple appliances the appliance with the smallest Btu input rating shall be tested first and remaining appliances tested in order of increasing input rate.

 

Induced draft heating systems shall be checked for spillage at the base of the chimney liner or flue. If a chimney is shared between and induced draft heating system and a natural draft water heater, spillage shall be checked at the water heater draft diverter. If the furnace is common vented with another furnace, make sure that flue gasses are not being directed out the second furnace during the off cycle

 

Vent draft pressure shall be measured at steady-state operating conditions for all natural draft heating and hot water appliances. Draft test location should be approximately 1-2’ downstream of the appliance draft diverter or at least two diameters distance away from the connecter. The test hole must be sealed with an appropriate plug after the test. Acceptable draft test results (BPI Standard) are shown below:
 

Outside Air Temperature

Minimum Draft Pressure Standard (Pa)

<10

-2.5

10-90

(T_out /40) - 2.75

>90

-.05


 

Note 1 inwc = 249.09 pa

Example to convert inwc to pa: -.02 inwc x 249.09 = -4.98 pa
 
 
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