Happy New Year. Today, I am nerding-out on you about hot water tanks.

The basics of hot water:

Direct-fire tanks are typical in Massachusetts. These are the gas or electric tanks that run a flame under a tank of water. When you open your faucet, you use some of that 30- or 40- or 50- gallons of hot water that has been sitting there, hot and ready for you.

Indirect-fire tanks are hot water storage tanks that do not have their own flame for heating. The hot water comes from your boiler. It’s kept in the tank until you open your faucet.

Tankless systems use a smaller quantity of very hot water mixed with room-temperature water, to deliver hot water to your faucet.

  1. The old-fashioned kind of tankless system is part of your home heating boiler. Some of the water circulating in your boiler is plumbed into a separate corner of the boiler. That water is super-heated, so that it is still hot, when mixed with cold water. When you open the faucet, you get this combination of super-heated and cold tap water, giving you about 120 degrees of hot water.
  2. Newer style tankless systems are stand-alone water heaters that super-heat the water you need, when you need it. When you open your faucet, you get the super-heated water mixed with cooler tap water.

Today, I am sharing a video from a kindred-spirit house nerd, Matt Risinger, who cut open some dead hot water heaters, to show you what’s inside.


Good words to know about your hot water heater:

Scale: This is the mineral residue that collects in the tanks.

Anode rod: Anode rods are metal rods that attract scale. This keeps the scale from collecting on the wall of the tank. They are made of magnesium, aluminum, or zinc.

Heat source/efficiency: Stand-alone tanks use gas, propane, or electric to heat the water in the tank.

Energy Guide label: It’s yellow; look for it on the back of the hot water heater. Hot water heaters are efficient, based on the efficiency of the heater unit and the insulation in the tank walls. Choose one that is rated in the lower one-third of the scale. It is likely to have better insulation.


Flushing the tank and replacing the anode rod will extend the life of your hot water tank.