Unsecured Thermal Expansion Tanks: A Flood Waiting To Happen

Unsecured Thermal Expansion Tanks: A Basement Flood Waiting To Happen

Something that home inspectors run across fairly often is thermal expansion tanks that are improperly installed (left unsupported) when installed horizontally. This situation can allow the tank to snap off due to the weight of water inside the tank and the result is your basement flooding which can result in considerable damage including your HVAC system, water heater, breaker panel, and pretty much everything else in your basement.

Thermal expansion tanks are required by modern plumbing codes when there is a check valve installed at the water meter. Check valves (single or dual) are typically required with all modern public water systems. Without a check valve, thermal expansion in your plumbing system could actually occur back through your water meter. Thermal expansion is the expansion and contraction of water in your supply water system due to heating and cooling of the water and helps prevent excessive water pressure in your plumbing system which can damage your water heater, pipe fittings, or any other water-using appliances. With a check valve present, it presents this expansion from happening beyond the valve (back towards the street) meaning an alternate means of thermal expansion needs to be provided in your supply plumbing system. A thermal expansion tank provides for this. The tank can be installed anywhere between your water meter’s downstream side (house side) and your water heater.

Thermal expansion tanks can be installed either horizontally or vertically. They are most often installed near the water heater on a copper pipe stub. When installed horizontally, a strap must be installed around the thermal expansion tank’s bottom and is typically secured to a floor joist directly above the thermal expansion tank. There are only a few pipe threads securing the thermal expansion tank to the pipe to which the tank is attached. As thermal expansion in your plumbing system occurs, some water will fill the thermal expansion tank causing it to get heavier. Water weighs approx. 8.2 lbs. per gallon. I’ve seen and heard of numerous instances of thermal expansion tanks snapping off of the pipe due to the weight of this water and the few pipe connections holding things together. The homeowner hears water running but initially has no idea where it’s coming from. They go down to their basement and find full city water pressure flooding their basement until they are able to run over to the main water shutoff valve to turn the water supply off to the home. By this time, damage is likely already done. What happens if nobody is home when this happens? Even if you have a water heater pan with a pan alarm installed under your water heater, it may not catch any water or alert the alarm if 40~80 psi water pressure is shooting out sideways into your basement and not running down the side of the water heater into the pan.

Finding this installation method is very common and indicates a poor quality water heater installation warranting immediate repair by a licensed plumber before the thermal expansion tank snaps off of its pipe. I have no idea why so many plumbers don’t use common sense when installing thermal expansion tanks.

The below photos each show thermal expansion tanks which have been properly installed with straps. These straps take stress off of the pipe/tank connections.

When installed vertically, no other means of securing the thermal expansion tank is needed. As the thermal expansion tank takes on water in the vertical position, the weight will be concentrated on the tank’s bottom where it connects to the cooper pipe feeding it.

Newer thermal expansion tanks installations (consult your tank’s manufacturer) generally now require they only be installed vertically (aka upright) and no longer permit horizontal installations, partially due to the common issue with faulty, unsecured tank installations leading to snapped off tanks and flooded homes. A good video that summarizes a thermal expansion tank installation can be found here (courtesy of KC Water Heaters): https://kcwaterheater.com/how-to-install-an-expansion-tank/

All homeowners should check to see if they have a thermal expansion tank installed and, if so, ensure that if it is installed horizontally, that a proper strap is installed. If not, call a licensed plumber for prompt repair.

Of related interest, I’ve also written a separate article which lists the top 10 plumbing issues found during home inspections: https://thehomeinspectorsnotebook.com/top-10-most-common-plumbing-issues/

Matthew Steger is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), and an electrical engineer. He can be reached at: matthew@thehomeinspectorsnotebook.com

No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.