We are working with our installer on this issue but would like more input. He suspects negative air pressure in the house

This is a gas burner installed in a room with all inside walls - center of a high ranch, bottom floor, no basement, exhausted to chimney. We had chimney inspected by chimney company - they confirmed that chimney is clear.

The burner was installed a year ago and we haven't had any issues until this past May. The burner started shutting down with a Blocked Vent error. It was happening daily at one point, then we turned off the attic fan and the issue was vastly reduced but is still occurring.

Is it negative house/room pressure? If so, how can it be addressed?

Any ideas would be appreciated.

  • 2
    What other gas appliances do you have such as stove, hot water, etc? Also what do you have for makeup air in your home?
    – Gil
    Jul 29 at 16:28
  • Most types of burners require outside air source for combustion, a pipe(extra to the chimney) that goes to the outside. Do you have one?
    – crip659
    Jul 29 at 16:41
  • The gas line was installed close to the time the boiler was installed. In the same room is a gas dryer. These are the only appliances requiring gas.
    – asuwish4
    Jul 29 at 19:50
  • As for air, the room has no outside walls. The outside dryer vent has a long tube that goes between rooms (inside the wall) and comes into this room through an opening in the sheetrock. When the house was first built, there was an aluminum vent built into the builder's grade door. The door was replaced with a ventless one many years ago. The burner was working fine until this past May.
    – asuwish4
    Jul 29 at 19:52

3 Answers 3


All well-equipped HVAC installers have a manometer in their truck to test fuel gas pressure. If the installer suspects negative pressure in the house, it is a simple matter to test it with his manometer. The manometer stays indoors, the tube goes to the outdoors. A window can be cracked open just enough to let the tube out without pinching it.

If there is negative pressure in the house, it will be displayed on the manometer as a positive reading. You can try turning on various appliances and blowers to see if the pressure changes. Range hood, bathroom exhaust, clothes dryer, attic fan, etc.

Remedies depending on the actual reading. There's no substitute for actually measuring the pressure, and your installer should have done this already if he suspected negative pressure.

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Is the burner on a space heater or ? It sounds like you have a negative pressure in the house. Gas ( and oil) need oxygen to burn. The resulting carbon dioxide goes up the chimney. The air/oxygen must be replaced or the burner could make carbon monoxide or go out. Modern equipment often has a detector to shut down rather than chance making carbon monoxide. Any appliance that has a flame must have air available . Houses are made air tight to avoid drafts so may starve burners unless there is an air entry source. My first house had a duct bringing outside air to the furnace. Since then I have added outside air ducts for all furnaces. My water heater is in a utility room with the gas clothes dryer so that room has an opening for outside air.

  • as mentioned in the comment above, The room has no outside walls. The chimney is in center of the house. The dryer vent duct goes out of this room, in the wall separating another two rooms and out to the back of the house. probably 7 to 8 feet long. If another duct was run in this way, how do you manage the air temperature?
    – asuwish4
    Jul 29 at 20:05
  • @asuwish4 Usually an air duct is placed close to the burner and it sucks in air from outside and that air is used for combustion, instead of down the chimney. Only a very little cold air comes into the house.
    – crip659
    Jul 29 at 20:40

Is it negative pressure - it sounds like it, if you unlatch the front door on a windless day does the air push it inwards?

How to fix: install a make-up air duct that feeds the furnace room with air from outside the house. the duct should be at-least as big as the flue.

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