Instant Hot Water Heaters

Cold water sandwich effect is a phrase used to describe the phenomena of a brief drop in hot water temperature as it flows from a tankless water heater due to the frequent operation of the unit.

As you know the tankless water heater supplies hot water to multi-points of use, such as, shower, tub, and faucet and are operated after regular breaks. Due to the frequent on/off operation of the tankless water heater, cold water is introduced to hot water giving a momentary fall in hot water temperat

This phenomenon is present in all tankless water heaters and can not be eliminated fully, particularly in gas-run tankless water heaters. Beacuse, the safety standards developed to insure the safe operation of water heaters demand a delay in the ignition sequence of all gas water heaters.

However some companies, such as, Rinnai, Titan, Bosch have successfully designed their models to reduce the cold water sandwich effect.

For instance, the technology built into the Rinnai water heaters is streamlined to address this problem effectively. Rinnai water heaters are microprocessor controlled and when water flow through them ceases, they remain in a “ready to fire state” for approximately one minute.

If water flowing through a Rinnai water heater begins within the first minute following water flow stoppage, the water heater will fire back up within 1 to 2 seconds. This minimizes the cold water sandwich effect in all Rinnai models.

The cold water sandwich effect can be tackled better by modifying the plumbing system. Rinnai has developed two methods to reduce the effect in residential hot water circulating systems.

According to the first method, the effect can be removed from circulating systems, by utilizing a small electric tank water heater.

The small water heater acts as a mixing tank to eliminate the cold water sandwich effect from the Rinnai water heater and it uses its electric heating element to offset the heat losses from the hot water circulating system.

In the second method, the cold water sandwich is removed by utilizing a small 2 to 6 gallon storage tank installed on the hot water outlet of the Rinnai water heater. This tank acts as a mixing tank to blend the cold water sandwich with hot water and thus eliminate the cold water sandwich effect.