Many refer to tankless water heaters as “instant” water heaters. It is true that as water comes in to the unit, it instantly is converted to hot water. This is compared to the tank unit where it takes time to heat all the water in the tank and keep the water hot. Tankless technology heats the water on demand. However, you don’t have instant hot water at your sink or shower, which is a myth of tankless water heaters, with either a tank or tankless unit. You still need to turn on your tap to let the cold water in the pipes out while drawing in the hot water to that location.
To truly get instant hot water at your taps, you need a recirculation pump or have all your taps in close proximity to your water heater. Smaller, tankless point-of-use systems that can be installed under a sink can provide instant hot water. However, because tankless technology has improved so that a single tankless unit can handle the hot water needs of a whole house, there needs to be a way to recirculate hot water in the pipes so that hot water can be more "instant" at the tap.
There are several different styles of recirculation pumps. You will want to get one that allows you to set a timer so you can recirculate water through a hot loop throughout your house, like a hotel, so that when a hot water faucet is turned on, there will be nearly instant hot water. You will save on your water bill as a result. So that you are not making the tankless water heater run for hours by recirculating hot water all day long, it is best to set the timer to start recirculating hot water a few minutes before you and your family usually take showers. Then have it stop recirculating until the next high demand for instant hot water occurs in your household.
While there are several pumps listed on the market, our two pumps of choice are the Watts 500800 Instant Hot Water Recirculating Pump and the Grundfos 595916 1/25 Horsepower Recirculating Pump. The beauty of these devices is that:
1) both are quiet (i.e., you don't know they are on unless you touch it and feel the tiny vibrations telling you it is pumping water), and
2) they are super easy to install.