House Water Heater Venting, How To Do It Right
Don’t forget to check House Brick Chimney Problems and Gas Water Heater and Furnace Chimney Flue Sizing posts - several of the water heater vent pipe conditions described below depend on properly operating and installed chimney!
There are two common types of gas water heater vents:
- natural draft - explained below
- induced draft - coming soon
Natural is still dominating, and as long as the property has a chimney dedicated for use with gas burning appliances, you can use this type of venting.
Typical connection of the gas water heater vent pipe would look more or less like one on the picture (one of the problems with this connection - missing screws at draft hood). There might be several variations… some good, and some bad of course.
Assuming, that you don’t know anything about this subject, this is how the gas water heater venting should be installed:
On top of gas water heater, in its center section, right above water heater vent, you should have a draft hood installed. It sits on 3-4 short legs, sometimes secured to the water heater top plate with screws, or (depending on design) has its legs shaped like pins or hooks at the end, inserted into the holes in water heater top cover.
For the gas water heater vent to operate properly its Draft Hood Has to be Centered over the vent hole, and its legs must be straight - any displaced or deformed draft hoods should be serviced / replaced if necessary, because they serve very important purposes and if not installed correctly, carbon monoxide gases may be expelled into the living space.
- Gas water heater draft hoods provide additional air for the combustion process gases, to be properly pulled out from the burner chamber (base of the water heater), into the water heater vent pipe and the chimney
- Gas water heater draft hoods act as a device, which in case of down-draft (a condition which forces air / wind back into the vent pipe / chimney), prevents air from extinguishing the gas burner.
Gas water heater draft hoods come in different sizes, and if you are replacing water heater, make sure, that the draft hood and the vent pipe match the new appliance. If the draft hood that came with your water heater has a top opening diameter designed for 3″ vent pipe, and you have 4″ vent pipe installed, use reducing connector.
However, if the gas water heater draft hood is larger, designed for a 4″ pipe - do not downsize it! / DON’T install reducing connector from 4″ draft hood to 3″ water heater vent pipe just to accommodate an old venting system. Replace the smaller size vent pipe with a proper / required size (most 30 gallons, 40 gallons, and 50 gallons water heaters use 3″ diameter vent pipe, some 50 gallons might require 4″, 75 gallons and more will call for 4″ and more - follow manufacturer recommendations and local code requirements).
Draft hood and water heater vent pipe connections should be secured with sheet metal screws - three per connection on a single wall pipe are recommended.
Gas water heater vent pipe material - for natural draft type just use galvanized steel pipe and don’t experiment with aluminum pipes, food cans with removed both ends, stainless steel sections, blue stove pipes, high temperature plastic tubing, flexible pipes…, etc.
Gas water heater vent pipe must continuously run upward towards the chimney entrance, raising not less than 1/4″ per linear foot, to provide proper draft. Some installation might be a significant challenge, or even become impossible, due to a water heater height and chimney flue connection level, in those cases, induced draft motor equipped water heater should be used.
Gas water heater vent pipes should be monitored periodically for corrosion and deterioration. Problems with proper drafting, and chimney conditions usually cause galvanized pipes to corrode. Small holes start appearing on their surface - most common areas are along the bottom portion and on connectors. At some point, corroded gas water heater vent pipe wall becomes very soft, and might fall apart when under even slight pressure.
Corroding gas water heater vent pipes should be replaced as soon as possible, to prevent possibility of exhaust fumes / Carbon Monoxide contamination.
Single wall gas water heater vent pipe can not be installed closer than 6″ from combustible materials (floor / wall framing, paper, etc.) such installation could create pyrophoric conditions and a fire-hazard (material will ignite spontaneously at significantly lower temperature if constantly exposed to heat).
Also, single wall gas water heater vent pipes can not be used in unheated areas like attic or garage (even if only partially penetrating that space) , because such installation will cause excessive condensation on vent pipe walls and compromise proper drafting - double wall pipe / B-vent type is required.
