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Domestic hot water coils
Domestic hot water coils are typically found in residential oil-fired, and some older gas fired hot water boilers. The coil’s job is to supply you with the domestic hot water that you use to shower, wash your hands and do laundry. The coil is basically a copper tube that is coiled up in a spring type pattern and submerged in the boiler. So that means the hot water that is in the boiler is surrounding the outer wall of the coil and heats the domestic water inside the coil. Here are two common things about coils that I see all too often when doing plumbing service jobs.
1. No tempering valve installed.
2. Complaints about not enough hot water, “my boiler is only a few years old and lately I’m running out of hot water after 10 minutes in the shower”.
Many times I see boilers with no tempering valve installed. This means you can easily be scalded. A tempering valve is a code required device that is installed in between the hot and cold pipes of the coil. It’s job is to temper and regulate the outbound hot water to a desired temperature not to exceed 140 degrees. Without a tempering valve, the outbound hot water temperature going to your bathtub and faucets, could exceed 190 degrees. Ouch! Also, a tempering valve could buy you more hot water in the shower. This is because the tempering valve draws a lower volume of water from the coil giving it more time to recoup.
As for number 2, “why is my hot water running out after 10 minutes?”… Let me count the ways. Think of a coil like an artery, any contaminates in the water act like platelets and begin to adhere to the ports. Contaminates in this case are usually calcium, iron and oxygen. These minerals and many others stick to the wall of the coil and slowly clog it up, affecting the volume of your hot water and cutting down on the heat transfer from the surrounding boiler water. People with well water usually have a higher concentrate of one or a combination of minerals and properties that quickly destroy coils.
There is however, an answer to getting more value and life out of your coil: install a booster tank. A booster tank is a non mechanical reservoir tank which is piped in series with your coil. The coil heats the water as usual and circulates the water to the booster tank. This helps you in two ways. It gives you an extra 50 gallons of hot water and more importantly, it keeps the water moving. Those contaminates do a number on the coil when the water is standing still. A circulator pump transfers the water between the coil and the tank frequently which hinders the adhesion of those destructive minerals.
Hope this was helpful