Venting Flue Gases

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    • #284759

      I recently had a gas hot-air furnace installed in the attic of my one-story home. The gas-fired hot water heater is just below it in a utility room and the 3 inch flue from this hot water heater was routed to the furnace flue in the attic. Recently, I noticed a negative draft at the top of the hot water heater when the furnace blower was on and Ive had condensation drip from the furnace flue before it goes through the roof. My contracter suggested getting fresh air into the utility room to allow for a natural draft of the hot water heater (he said my house was too tight). Ive installed a fresh air duct into the utility room (to the top and bottom of the water heater), but I am still experiencing condensation in the furnace flue. Could the water heater be causing a negative draft of the furnace flue? Would it help if I disconnected the hot water heater flue from the furnace flue and just ran the hot water heater flue straight up through the roof? If I did this does the new hot water heater flue have to be a certain distance from or above the roof peak (as fireplace flues need)? or a certain height above the roof if it isnt more than 10 feet from the roof peak?

    • #308473

      The negative draft and condensation can both be caused by excessive cooing of the chimney as the combustion products are passing through it. If the flue gases cool down to much, they lose their convection energy and drop back down the flue. And since H2O is a product of combustion, cooling the gases will also create moisture.: I recently had a gas hot-air furnace installed in the attic of my one-story home. The gas-fired hot water heater is just below it in a utility room and the 3 inch flue from this hot water heater was routed to the furnace flue in the attic. Recently, I noticed a negative draft at the top of the hot water heater when the furnace blower was on and Ive had condensation drip from the furnace flue before it goes through the roof. My contracter suggested getting fresh air into the utility room to allow for a natural draft of the hot water heater (he said my house was too tight). Ive installed a fresh air duct into the utility room (to the top and bottom of the water heater), but I am still experiencing condensation in the furnace flue. Could the water heater be causing a negative draft of the furnace flue? Would it help if I disconnected the hot water heater flue from the furnace flue and just ran the hot water heater flue straight up through the roof? If I did this does the new hot water heater flue have to be a certain distance from or above the roof peak (as fireplace flues need)? or a certain height above the roof if it isnt more than 10 feet from the roof peak?

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