Living with a gas water heater

Living with a gas water heater
 

This article addresses the unique properties of gas water heaters.  Water heater safety is often overlooked, and sometimes the water heater requires some maintenance or modification.   
The location of your water heater is critical so that the required combustion air and exhaust venting are provided.  Just because it’s been in the same location for ages, doesn’t mean it is safe or correctly installed.  Gas fired water heaters need to breathe just like us.  But we shouldn’t share the same air.  To be safe, and meet building codes, water heater combustion air must not come from the living area of the house.  Fresh outside air for combustion is supplied by venting from the outside or attic.  Usually a sufficiently large garage with air vents has enough volume to support complete combustion.  Lack of combustion air can cause an increase in the production of poisonous carbon monoxide.
It is important to properly vent the products of combustion (carbon dioxide, carbon monoxide, moisture etc.) to the exterior.  First, there is a flue draft hood (there should only be one) on top of the heater.  The flue vent is attached to it and because heat rises, the pipe must be sloped upward. The vent pipe gets hot so it must be kept away from combustible materials, one to six inches depending on type. This is not a place to use duct tape or paint (both combustible).  Don’t forget to go outside and look for the vent and be sure it has a cap on top. 
 As part of the venting system, older homes sometimes have a transite type pipe that is made of concrete with asbestos fibers.  Even though undisturbed transite is not likely to release asbestos fibers, it can cause other problems.  The hot exhaust gases tend to condense on the cooler walls of the concrete material and then deteriorate the metal connections below.  To be safe, use commonly available double wall vent pipe instead of transite.  Be sure to call an asbestos abatement contractor for removal and disposal of the old pipe.
 The adequacy of the gas supply is another safety concern.  Typically, the average water heater of up to 50 gallons is served with a half inch size pipe.  If another gas appliance like a dryer or furnace has been added to this line, it may not be big enough.  That means that without sufficient flow, the air/gas mixture is wrong and more carbon monoxide is produced creating a potentially deadly health hazard. 
An easily accessible gas shut off valve is critical in an earthquake or emergency.  The gas tubing connection should be flexible as we live in an earthquake prone region. Every time a water heater is replaced, the gas tubing must also be replaced.  Be sure to get the right size for your water heater.
Tankless water heaters, or flash heaters, are gaining popularity due to their energy efficiency.  However, they typically require significantly more gas and combustion air than a comparable tank type heater and there are some important differences in installation.  Because they require several times the amount of gas, a larger supply pipe is required.  The combustion air available in the average garage is not enough for one of these heaters and different venting may be necessary.   Venting of the much hotter exhaust gases requires special more expensive piping.  Before you buy, be sure to read the manufacturers installation instructions and factor in these extra costs.