| Generally speaking, tankless water heaters are | | | | tend to have a lower maximum capacity than gas |
| not compatible with hot water recirc or circulating | | | | heaters. |
| pumps due to the low flow rates on the pump | | | | On the other hand, if you want a lower |
| side, and over-temperature problems on the | | | | temperature, and you adjust the valve |
| heater side. | | | | accordingly by reducing the amount of hot water |
| They are however compatible with hot water | | | | and increasing the cold. But if that results in a hot |
| demand system pumps as long as the pump has | | | | water flow rate lower than the minimum required |
| enough power to create the flow needed to turn | | | | by the heater, it shuts off. |
| on the water heater. | | | | You aren't aware of the change until a minute |
| By installing a hot water demand system to work | | | | later when the cold water hits you. You |
| with your tankless water heater you will get your | | | | immediately re-adjust for warmer water and in a |
| hot water faster and save a lot of water at the | | | | minute or so it finally arrives. This is known as the |
| same time. It really turns your tankless heater | | | | cold water "sandwich" in the water heater |
| into a green product. | | | | industry. |
| Problems with tankless water heater flow rates | | | | So it's very important to get the correct size |
| Tankless water heaters require a minimum flow | | | | tankless water heater, not to big and not too |
| of water to turn on or keep the heater turned | | | | small. |
| on. Drop below that flow rate and the heater | | | | Hot water demand systems save water and |
| shuts down. Typical minimum flow rates are 1/2 | | | | energy |
| to 3/4 gallons per minute. | | | | Since hot water demand systems do not run |
| If you want to use one of those "luke-warm" | | | | continuously, only for a few seconds to get the |
| circulating systems like the Autocirc1, RedyTemp, | | | | hot water to the fixture, they work fine with |
| or Grundfos systems you are out of luck. They | | | | tankless water heaters, as long as they can |
| don't produce enough flow to turn on the water | | | | produce the required minimum flow rate. Some |
| heater, so they would not be of much use. | | | | models will and some won’t. |
| There are some models of tankless water | | | | A demand type hot water pump only pumps |
| heaters that can be used with traditional circulating | | | | water from the heater to the fixture when you |
| pumps. However, it kind of defeats the purpose | | | | “demand” it by pressing the start |
| of the tankless water heater since you will use | | | | button. When the hot water reaches the pump |
| substantially more energy with this type of recirc | | | | it shuts off. At that point the hot water piping |
| system than without it. You will save water | | | | from the heater to the fixture is full of hot |
| though. | | | | water, and you can turn on the faucet to receive |
| Potential shower problems with incorrectly sized | | | | nearly instant hot water. |
| tankless water heaters | | | | |
| If your tankless water heater is sized too large or | | | | Typically hot water demand pumps can pump |
| too small you may suffer temperature control | | | | water at twice the rate of most low-flow fixtures |
| problems taking showers and the like. The | | | | found in today’s homes. |
| temperature of the shower is controlled by the | | | | |
| ratio of hot water to cold water produced by the | | | | You save energy with your tankless water heater |
| mixing valve. | | | | and you save water with the demand pump and |
| If you want hotter water then you adjust the | | | | you save money from both, while adding |
| valve for more hot and less cold water. If your | | | | convenience for yourself. |
| heater is already putting out the most hot water | | | | |
| it can, then increasing the flow will simply lower | | | | Be green, help reduce your carbon footprint, and |
| the temperature since the heater won't be able | | | | install a demand pump on your tankless water |
| to keep up. This is more of a problem with | | | | heater today! |
| electric heaters than gas because electric units | | | | |