Should a tankless water have a recirculating pump?

The answer is yes! But it needs to be done correctly or it could use more energy and make your hot water less convenient than without it and waste a lot of water at the same time. Read below to see the different options for using a recirculating pump with a tankless water heater so save energy and water. Or give us a call with any questions at 209-352-4294

A condensing tankless water heater with internal recirculating pump and buffer tank with dedicated recirculating line.

This is by far the most efficient and convenient way to heat water and waste less water. The built in recirculating pump and buffer tank work together to have hot water ready when you need it at the fixture, and you don’t run out like with tank models. The hot water can be controlled with a thermostat and timer so the unit only kicks on when you have it set, and in those time periods only when the water in the line falls below around 90 degrees. This limits the amount of power the pump uses, and how often the burner fires keeping cost down, and efficiency high. Many times adding a tankless water heater with internal recirculating pump and buffer tank with a dedicated recirculating loop from the furthest fixture from the water heater can cut waiting times for hot water from a couple of minutes to around 10 seconds which can save thousands of gallons of water per year. If there is no existing recirculating line many times it can be added with copper or pex. If the hot water line and the recirculating loop are both well insulated the efficiency is greatly increased.

A condensing tankless water heater with internal recirculating pump and buffer tank without a dedicated recirculating line.

Some of the newest models of tankless water heater we are installing can use a crossover tee at the furthest sink from the water heater. This tee will let some of the cooled off water in the hot water line into the cold water line as the internal pump in the water heater pushes the hot water closer to the furthest fixture. When the water at the fixture heats up the crossover tee stops letting water through so the cold water line doesn’t get hot, and your tankless water heater stops running. This is a good solution if you want the convenience of the recirculating line but can’t add the insulated recirculating loop because of cost, or because the pipes are not accessible to run a line back to the water heater.

A tankless water heater with an added recirculating pump and buffer tank.

This is an option if someone didn’t want to buy the more expensive unit up front, and wanted to buy a standard tankless and add on recirculation later. Unfortunately this installation ends up costing more and the system does not work as well together. If an older tankless is installed we have used this method to cut wasted water from waiting for hot water to get to fixtures. A tankless that is only a few years old doesn’t need to be replaced just to cut down on wait time and save water !

 

A standard tankless water heater with a recirculating loop and no buffer tank.

This is a bad idea but happens when an installer doesn’t understand how a tankless works, or is trying to cut corners. The pump can get the tankless to kick on but it shuts off every time the pump kicks off. When a tankless kicks off it doesn’t start making hot water again immediately when it is turned back on. Cool water enters the heat exchanger and passes through without being heated completely or at all. This means when you turn on your shower it feels warm because the pump pushed hot water through the line, but when the cold water that goes through the heat exchanger without being heated from startup comes through the line you get a cold shot of water in your shower. This wastes a lot of energy with almost no real benefits. We recently saw one of these systems that the owners had been dealing with for years. The pump also had no timer so it was running any time the water temperature dropped 24 hours a day making their “more efficient” tankless water heater extremely inefficient and giving them intermittent cold shots of water in their showers. When offered the more efficient condensing unit with internal recirc pump and buffer tank to eliminate the cold they quickly decided it was a good idea. They had never been told about the right way to do it and thought the cold water shots were normal for a tankless water heater.

Optimized Plumbing is a Sonora Ca based plumbing contractor specializing in tankless water heaters, hybrid heat pump water heaters recirculating systems, hydronic heat, radiant heat, and plumbing service and repair. We service all areas of Tuolumne and Calaveras counties including the towns of Angels camp, San Andreas, Murphys, Arnold, Twain Harte, and Copperopolis.