Tankless Coil Water Heaters
Pros and Cons

Install a tankless coil water heater and take advantage of the hydronic boiler, gas, or oil-fired furnace to heat your home and domestic water at the same time. Check out buying and installing tips of the tankless coil systems for residential heating, including pros and cons.

What is a tankless coil?

A tankless coil water heater is designed to perform as the coil-type heat exchanger, installed in the boiler or furnace, and used to heat domestic water.

As the coils are immersed inside the hydronic boiler, they become a part of the home space heating system. The heat is transferred from hot water inside the boiler to water that is running through the tankless coil exchanger, and further to the water fixture, for dishes, shower... There is no water storage, so water is heated on demand providing a continuous supply.

Tankless coil devices are designed to provide an optimal heat transfer while saving money on the total installation cost. If the cold water flows too quickly through the coil, it will lower the outgoing hot water temperature. By installing a flow regulating valve on the incoming cold supply, you can control the temperature.

Pros and cons

The advantage of the tankless coil systems is in the absence of the storage tank and standby heat loss, which eliminates the need for purchasing a separate heating system - resulting in money savings. Water is heated on demand, as it flows through the heat exchanger whenever the hot tap is open.

The tankless coil can also work as a supplemental heater.

A home heating system has to work to produce hot water. This is the main drawback, as the system is less efficient when space heating is not required during the summertime. When the home heating system is used more frequently during cold weather, water heating also becomes more efficient.

This is why tankless coil water heaters are primarily seen in colder climates.

Moreover, to help tankless coil water heaters overcome the problems with the low efficiency during the warmer months, the coil system is combined with the storage tank. Now, the whole system has to be upgraded with the pump and other controls. The boiler will not operate all the time, only when there is a call from the thermostat for heating.

The pump will run the colder water near the bottom of the storage tank through the tankless coil and moved to the top of the storage tank providing a stable temperature. The circulation will stop when the temperature on the thermostat is satisfied.

One of the reviews or studies done by " Consumer Guide to Home Energy Savings" is that in non-winter months, tankless coil water heaters can consume three BTU's of fuel for every one BTU of hot water these units provide.

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Problems and how to solve them

If you notice that the water flow is lower than usual, mineral deposits or rust might have built up in the coil exchanger. This is one of the frequent problems as the tankless coils are built from small size pipes, which are subjected to clogging. To avoid further problems, the unit has to be flushed.

Use the white vinegar, citric acid, or any other available solution, and pump it through the tankless coil, therefore flushing the mineral deposits out. It is essential to have the isolation valves installed to isolate it from the potable water supply and make the service easier. This is not a simple DIY project, the project needs a specialized pump, so the recommendation is to call a plumber.

If the coil leaks, it might result in potable water contamination with the boiler water, or even worse, it might damage the boiler. Leaks are caused due to the failed connections in the coil tubing or where there are plumbing connections. The pressure and the amount of hot water will be reduced.

An improperly adjusted mixing valve is another reason for the insufficient hot water supply, except for the mineral deposits.

As explained before, tankless coil water heaters are recommended for homes located in northern and colder areas, where the furnace and boilers operate most of the year. A supplemental water heating system should be provided in warmer regions, where the heating season is shorter.

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