Continuing my theme of common problems I see on home inspections, today’s post is going to discuss tank style water heaters. These water heaters are simple tanks with a cold water pipe coming in and a hot water pipe coming out. At the bottom of the tank is either a gas fired burner or electric heating element that warms the water to the desired temperature. As warm water is used cold water comes in and travels to the bottom of the tank via the drop tube. Being warmer and less dense than the cold water, the warm water stays at the top of the tank instead of mixing. This is a good thing because the top is where the warm water is drawn out of the tank. There are instances where the drop tube has deteriorated or broken off allowing the cold water to come in at the top, mixing and cooling the hot water right where it is taken out of the tank. This situation severely limits the amount of useable hot water from the tank. While this problem is not likely to be identified in a non-invasive visual home inspection, I mention it here to possibly assist those with unexpectedly low amounts of hot water. Normally the drop tube is replaceable and inexpensive.
When I walk up to a water heater I like to start with the incoming water piping. First I observe the pipe material going into the tank and check for leaks and that there is a shutoff valve to turn the incoming water off so the tank can be changed without turning water off to the whole house. Next, if the pipe coming into the tank is a dissimilar metal than the nipple on the tank, say copper going into a galvanized nipple, check for a dielectric union. This is a special union that prevents the flow of electrons from one metal to the other preventing corrosion. The hot side of the piping is generally the same as the cold but there generally isn’t a shutoff valve.
With the water piping taken care of it is time to move on to the gas piping if it’s a gas fired water heater. There are four main things to check: leaks, shutoff valve, sediment trap, and union. The gas piping is usually black iron but you may also see flexible stainless depending on what is allowed in your area. When you first approach the water heater be aware of any sulfur or rotten egg smell. Any sulfur smell likely indicates a leak. Be sure to pay attention to this when you first enter the area because the longer you are exposed to the smell the less it is noticed. For first timers it is probably easier to start at the gas valve located low on the side of the tank and follow the gas line backwards. Just upstream from the gas valve should be a union. The union allows the gas line to be disconnected from the water heater without taking all the piping apart. Continuing upstream from the union you should find a sediment trap. This is normally a three or four inch nipple extending down below the horizontal run of pipe. It allows any debris in the gas line to fall out of the stream preventing clogged burner orifices. Now continue traveling upstream from the sediment trap and you should find a shutoff valve within a few feet. Its’ purpose is to turn gas off to just the appliance for service.
With the piping taken care of it’s time to inspect the tank itself. Look for heavy rust on the tank shell and soot or burn marks caused by flame roll-out of the burner compartment. Towards the top of the tank is usually a brass valve coming out the side with a pipe running down to near the floor. This is the temperature and pressure relief valve and extension. Its’ purpose is to relieve pressure by venting hot water out the valve, should the heater malfunction and over heat, preventing a water heater explosion. This also means in the event of the valve venting that scalding hot water will forcefully spray all over. The purpose of the extension is to safely vent this spray to within six inches of the floor preventing anyone nearby from getting severely burned. There should always be a TPR valve and extension terminating within six inches of the floor.
If you see water on the floor just below the extension pipe this means the valve has opened or leaked. Sometimes the valve needs to be replaced. Other times there may be a back flow preventer in the home preventing the water from expanding into the city water supply as it is heated which raises pressure in the tank causing the valve to drip. If this is the case, an expansion tank should be installed between the water heater and back flow device. Back flow devices are normally located where the water comes into the home.
With the piping and tank done it’s time to inspect the exhaust vent on gas fired heaters. Electric water heaters won’t have this vent because there are no combustion gases to vent. At the top center of the tank will be a metal collar raised off the top of the tank about an inch with the metal duct attached to it. This is called a draft hood. The draft hood should be firmly secured to the tank, commonly with screws. Also the metal duct running out the top of the draft hood should be firmly secured to the draft hood with screws. I mention screws instead of duct tape because the vent gets hot and tape will come loose. I often see draft hoods and vent not secured at all and just sitting on top of the heater. This is a bad idea because if it is bumped out of proper alignment, dangerous carbon monoxide will discharge into the area every time the burner runs.
Now inspect the duct coming out of the draft hood. It should slope up at least a quarter inch per foot. In homes where the water heater and furnace both vent into a common flue in the chimney the smaller appliance (normally the water heater) must enter the flue above the larger appliance vent. This is to keep the larger appliance from over-powering the smaller appliance vent and back-flowing exhaust down the smaller vent into the home. The actual vent pipe is normally single wall or double wall. Single wall pipe just slips together and is held with screws. Double wall has a twist lock type connection. The reason I mention the different styles of vent pipe is because the required clearances to combustibles are different. With single wall you should maintain a six inch clearance to combustibles. Double wall or “B Vent” can be as close as one inch to combustibles. You may also run into a high efficiency water heater with a powered vent. These are less common and have to be installed per manufacturer’s instructions so I won’t comment further.
Last but not least is the water heater drain valve. As its’ name states, it’s for draining the water out of the tank. You generally want to do this for two reasons. The first is to make the tank lighter so it can be removed. The second is a yearly maintenance function. Every year you should attach a hose to the valve and run it to a drain. Open the valve all the way and allow the water to flow out down the drain for a few minutes. What this does is help pull sediment off the bottom of the tank increasing heat transfer from the burner. The burner won’t have to work as hard saving you money and extending the life of the tank.
While this isn’t an exhaustive list of everything to check on a water heater, it should handle 90% of the water heaters you are likely to encounter.
© Darren Taylor and RacineHomeInspector.com, 2014. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Darren Taylor and RacineHomeInpsector.com with appropriate and specific direction to the original content.