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How can I vent through the sewer?

Introduction to Sewer Venting​

A popular alternative to venting through a chimney is venting into the sewer pipe. This method may be feasible depending on your house's construction, as air pushed into the sewer pipe can travel up through the sewer standpipe within your home. Venting directly into the actual sewer system is also a possibility.

Safety and Smell Concerns​

Generally, venting into the sewer is considered safe. If someone works in the sewer nearby, they might detect the sweet, pungent aroma from your crop, but they cannot pinpoint its source. Since large pipes are far from individual homes, the smell has ample time to dilute. The sewer system's natural odor can help mask your crop's fragrance. However, ensure nearby manhole covers do not leak excessive noise or smell. The underground sewer system also dissipates and cools exhaust heat, providing protection against infrared detection.

Preparing for Sewer Venting​

To begin, locate the sewer pipe in your basement, which connects to the toilets on upper floors. You should find a Y connection with a cap near the basement floor. Houses may have metal, ABS, or PVC plastic sewer pipes. Use a pipe wrench to remove the cap or replace it with a new one from a hardware store, if necessary. The hole should be 3 to 4 inches in diameter, though sizes may vary.

Caution: Sewer fumes can be hazardous. Exercise caution when removing the cap and ensure the fan stays on to prevent backflow into the home.

Fan Installation and Setup​

Visit a hardware store to purchase connectors and aluminum flex ducting for connecting a fan to the hole. Centrifugal inline fans are the most efficient option, but squirrel cage fans work as well. Inline fans consume less electricity but may be noisier.

The fan's inlet and outlet ports should be 6 inches in diameter. Use a reducer to connect the 6-inch port to a 4-inch aluminum dryer ducting, and attach it to the sewer hole using duct tape.

Testing the Setup​

To test your work, stand outside the basement door and hold a lighter to the crack at the door's bottom. If the flame is drawn inwards, you have successfully created a 'negative pressure' environment, preventing odorous grow room air from entering the house and containing the smell.

Note: Sewers contain methane, a smelly and potentially explosive gas. Keep these gases away from any pilot lights, such as those on water heaters.
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