Attach Air Intake to Old B-Vent

Started by dforsman, March 04, 2019, 12:09:10 PM

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dforsman

I'm in the process of moving my dryer from one location to another in my home.  I want to make sure once the move has been completed that the dryer exhaust is not near the fresh air intake for the furnace.  I was wondering if it might be ok to use the old B-vent for the fresh air intake as it is no longer being used and extends all the straight up through the roof.

As you can see from the diagram I would attach the B-vent pipe to the fresh air intake.

Thanks for your help.

Admin

Yes, just make sure the dryer vent is at least 3' away from the furnace intake outside.  I assume there's no other appliance using that chimney so there's no problem installing a 6" x 4" reducer and using 4" insulated flex as the outdoor air supply.  Terminate it within 1' above the largest BTU burner.  You would also need to install a screen on the chimney cap you just turned into an intake.

Porcupinepuffer

What is the deal with the white pipes? Is one for a water heater and one for the furnace? And your furnace room is using the 4" fresh air intake as the makeup air?
I would just make sure you're dryer vent is 1' from the fresh air intake outside. Since it isn't mechanical, it only requires 1 foot. I wouldn't use a chimney as a fresh air as it's too un-reliable with either updraft issues or downdraft issues.


Update: Whoops! I meant 3 feet. Too tired that day.

Admin

I think you're refering to Table 5.2 and the regulator vent clearance to non mechanical or mechanical air intakes.  An HRV intake would be considered a mechanical intake but a 2 pipe furnace intake is not considered a mechanical air intake.  The same way some older outdoor air supply vents used to connect directly to the return air and use the mechanical fan to draw in air.  This was also not considered a mechanical air supply.  For some reason inspectors only consider the HRV to be a mechanical air supply.

A residential dryer vent requires 3' even from a non mechanical fresh air.

QuoteClause 7.5.2 - A moisture-exhaust duct shall not terminate within 3 ft (1 m) in any direction of any pressure regulator vent termination or fresh-air intake.

QuoteClause 8.3.7 - An air-supply opening shall not be located within 3 ft (1 m) of a moisture exhaust duct. In the case of Type 1 gas clothes dryer, this separation shall be not less than 3 ft (1 m) and in the case of Type 2 gas clothes dryer not less than 10 ft (3 m).

Note: A moisture-exhaust duct (e.g., a gas or electric clothes dryer discharge or spa exhaust) is considered to interfere with the combustion air intake when located within 3 ft (1 m) of the air intake.

Good point about negative air and something worth testing, but ultimately using the abandoned chimney is allowed.  If the house was under negative air it would only bring fresh air down the chimney and to where we need it anyway.  The only issue would be the Building Code.  Depending on the outdoor design temperature in your area the first 3m of the outdoor air supply may require R8 insulation.  Being that the chimney is B-Vent I wouldn't worry about condensation though.

QuoteClause 8.3.1 - Except as specified in Clauses 8.3.3 and 8.3.4, a duct shall be used to provide the outside air supply required by Clauses 8.2.1 and 8.2.4. The duct shall
(a) be of either metal or a material meeting the Class I requirements of CAN/ULC-S110;
(b) communicate directly with the outdoors;
(c) be of at least the same cross-sectional area as the free area of the air-supply inlet opening to which it connects; and
(d) terminate within 1 ft (300 mm) above, and within 2 ft (600 mm) horizontally from, the burner level of the appliance having the largest input.

Clause 8.3.3 - An opening may be used in lieu of a duct to provide the outside air supply to an appliance as required by Clauses 8.2.1 and 8.2.4. The opening shall be located within 1 ft (300 mm) above, and 2 ft (600 mm) horizontally from, the burner level of the appliance having the largest input.