All these Tanks…Expansion tanks, Pressure Tanks and Water heaters.

There are a few types of Tanks that are common to see in houses. I say common because not each is necessarily going to be in each house. The one that most people think about is the water heater. Now, more recently there are many times where this is not even seen because tankless water heaters are just as common. I’ll talk a little more about tankless in a bit, but for now, let’s start with traditional water heaters.

Water heaters take cold water and use an energy source to heat it. The energy source may be electric, gas or oil. Oil really comes into it in one situation, which we’ll touch on at the end of this. In gas setups, water comes into the tank and the gas is used to fire up a flame that heats it from the bottom. One telltale sign of this is if your water heater has a flue (exhaust vent) at the top. Some places even require a powered exhaust vent on new installations now. If you’re burning something, the exhaust needs to get out. Once the water’s heated, it stays in the tank until you turn the hot water on at a faucet, and then it pulls it from the water heater. With electric water heaters, it’s actually heating elements inside the tank that will heat the water. This is done without combustion, so there is no need for an exhaust to vent from the water heater. It keeps the water stored in them at a temperature and then turn back on to reheat the water whenever it drops too low or needs to refilled. That is the basics on how gas and electric water heaters work. 

Now I mentioned Oil as a potential source too. This is common in situations where there is no actual separate water heater and the heating system boiler is acting as the water heater as well. While a completely suitable setup, you should make sure you stay on top of annual service in this situation as your boiler is providing both heat and hot water. Also not uncommon with this situation, is a water storage tank. This looks like a water heater, but they simply store the water and then recirculate it to the boiler when it is below its storage temperature for reheating. There are actually 2 dead giveaways that they are storage tanks and not water heaters. First, it will not have any power source going to it that is capable of providing enough power to heat the water. You’ll see some small electronics on it sometimes, but nothing that could transfer enough power through it to heat 40 gallons. The second dead giveaway, and this is true of every water storage unit I’ve come across, it says it on the label.

Expansion tanks, or thermal expansion tanks, are another tank to see during an inspection. These are required to be installed on all closed loop water systems; quite frankly they’re not a bad idea to have on all systems to help prolong the life of your plumbing. What’s a closed loop water system? It’s where the water flows one way. If your water is provided by the town or city, you have a backflow preventer or pressure reducing valve on your waterline, it’s a closed loop system. Think of it as preventing water from going backwards because it might contaminate the source if it does. Why is the expansion tank required? Well when you heat water, it expands, creating pressure. That pressure is originating in the water heater and pushing on the water heater tank, which is by design. That pressure can’t be released until you turn the faucet on and call for that hot water, releasing that energy. The expansion tank, installed on the cold water supply side, allows some of that water pressure that is being pushed on to go up into the tank and safely equalize your plumbing lines until that time. That tank is essentially just air, waiting to be displaced with water pressure when needed. If the tank is not there, that water pressure is pushed back onto the water lines.

Pressure tanks for Well water systems are also a common item to see in homes, at least in Massachusetts. These tanks often get confused and mistaken for water heaters. While they store some water in them, they definitely do not heat it. Your well pump turns on and well…that pump is a motor going in there, not a big one like your car, give it a break. It’s sucking up water and pushing it into your house. Once it gets into your plumbing it will be connected almost immediately to the pressure tank. The tanks will be filled with water at the bottom half, and air at the top half. This helps maintain the pressure for the water in your house. While well systems don’t technically require a pressure tank, I’ve never seen an installation without one, nor have I ever spoken to a plumber who works on wells that has not felt they should be there.

While those are the 4 most common tanks to come across, it’s also not uncommon nowadays to see other “tank” looking devices with plumbing attached to them. Water filtering and softening systems are not often confused for these, but they definitely can be if you don’t know what you’re looking at.

As mentioned before, tankless water heaters are also commonplace to see. There does tend to be some confusion on them with a perception vs. reality in terms of the use. I remember a time when they were more being advertised as “On Demand” vs tankless. It is true that they heat water on demand. You turn the hot water faucet on and the tankless water heater turns on to heat the water and send it over to you. However, it does still take time for the water heater to heat the water. On demand does not equal instant in this situation. That being said, tankless water heaters tend to be more energy efficient because they’re not keeping a large amount of water at the set temperature.