Water heater venting

[Greg Frazier]

I inspected a house with an unlined chimney with two separate flues. Each flue had a cleanout door. The water heater vented into the left flue and was backdrafting badly. The vent connector rise was less than 6 inches as required by the manufactures installation manual. Whirlpool manual says "CAUTION VENT CONNECTORS MAY NOT TERMINATE WITHIN A CHIMNEY
FLUE SERVING A FIREPLACE UNLESS THE FLUE OPENING IS PERMANENTLY SEALED." Does this mean the cleanout door must be sealed as well as the chimney opening where the vent connector enters? By the way, the cleanout door can't be sealed right now anyway. It is propped open by a gas line tapped from the water heater going up to a gas log. There were other problems as well.

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[Eric Barker]

Two flues, a fireplace and water heater. Is there something that makes you think that the water heater is venting into the fireplace flue? The clean out is generally for the fireplace only and should be kept closed to permit proper drafting for what ever is using using the flue.

In any event, any unlined flue needs evaluation.

[Dana Bostick]

I inspected a house with an unlined chimney with two separate flues. Each flue had a cleanout door. The water heater vented into the left flue and was backdrafting badly. The vent connector rise was less than 6 inches as required by the manufactures installation manual. Whirlpool manual says "CAUTION VENT CONNECTORS MAY NOT TERMINATE WITHIN A CHIMNEY
FLUE SERVING A FIREPLACE UNLESS THE FLUE OPENING IS PERMANENTLY SEALED." Does this mean the cleanout door must be sealed as well as the chimney opening where the vent connector enters? By the way, the cleanout door can't be sealed right now anyway. It is propped open by a gas line tapped from the water heater going up to a gas log. There were other problems as well.

It's always been my understanding the gas appliances should not ever be vented into unlined chimney flues due to the fact that the exhaust from them contains a lot of moisture which, in combination with the soot etc., can become acidic and deteriorate the chimney and mortar.

[Bob Harper]

That reference means they recognize you can use any flue for venting as long as it meets the requirements for that appliance and the other code sections. Therefore, in order to vent a water heater or furnace into a fireplace flue, you would have to permanently block off the fireplace from the flue. The WH would then have to vent directly into the first flue tile. However, you still need at least 12" of flue to extend below the breech connection, which means the smoke chamber. You need access into the smoke chamber to inspect and clean out debris. The flue also would need to be inspected for suitability for that application (Level II). Since fireplace flues are generally much too large for heaters, it would require a listed liner regardless. If you still wanted to do this, you would have to remove the vented gas logs.
HTH,
Bob