Water Circulating
Water Circulating fitted new radiator to my 1997 323ise and the temp guage keeps rising even idling, water circulating ok help? water pump and thermostat appear ok I assume that the car was run...
Water Circulating
Tankless Water Heater Pumps & Hot Water Circulating Systems
Generally speaking, tankless water heaters are not compatible with hot water recirc or circulating pumps due to the low flow rates on the pump side, and over-temperature problems on the heater side.
They are however compatible with hot water demand system pumps as long as the pump has enough power to create the flow needed to turn on the water heater.
By installing a hot water demand system to work with your tankless water heater you will get your hot water faster and save a lot of water at the same time. It really turns your tankless heater into a green product.
Problems with tankless water heater flow rates
Tankless water heaters require a minimum flow of water to turn on or keep the heater turned on. Drop below that flow rate and the heater shuts down. Typical minimum flow rates are 1/2 to 3/4 gallons per minute.
If you want to use one of those "luke-warm" circulating systems like the Autocirc1, RedyTemp, or Grundfos systems you are out of luck. They don't produce enough flow to turn on the water heater, so they would not be of much use.
There are some models of tankless water heaters that can be used with traditional circulating pumps. However, it kind of defeats the purpose of the tankless water heater since you will use substantially more energy with this type of recirc system than without it. You will save water though.
Potential shower problems with incorrectly sized tankless water heaters
If your tankless water heater is sized too large or too small you may suffer temperature control problems taking showers and the like. The temperature of the shower is controlled by the ratio of hot water to cold water produced by the mixing valve.
If you want hotter water then you adjust the valve for more hot and less cold water. If your heater is already putting out the most hot water it can, then increasing the flow will simply lower the temperature since the heater won't be able to keep up. This is more of a problem with electric heaters than gas because electric units tend to have a lower maximum capacity than gas heaters.
On the other hand, if you want a lower temperature, and you adjust the valve accordingly by reducing the amount of hot water and increasing the cold. But if that results in a hot water flow rate lower than the minimum required by the heater, it shuts off.
You aren't aware of the change until a minute later when the cold water hits you. You immediately re-adjust for warmer water and in a minute or so it finally arrives. This is known as the cold water "sandwich" in the water heater industry.
So it's very important to get the correct size tankless water heater, not to big and not too small.
Hot water demand systems save water and energy
Since hot water demand systems do not run continuously, only for a few seconds to get the hot water to the fixture, they work fine with tankless water heaters, as long as they can produce the required minimum flow rate. Some models will and some won’t.
A demand type hot water pump only pumps water from the heater to the fixture when you “demand” it by pressing the start button. When the hot water reaches the pump it shuts off. At that point the hot water piping from the heater to the fixture is full of hot water, and you can turn on the faucet to receive nearly instant hot water.
Typically hot water demand pumps can pump water at twice the rate of most low-flow fixtures found in today’s homes.
You save energy with your tankless water heater and you save water with the demand pump and you save money from both, while adding convenience for yourself.
Be green, help reduce your carbon footprint, and install a demand pump on your tankless water heater today!
About the Author
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