DHW
Domestic Coils in Boilers
The domestic coil located inside many boilers is probably one of the most inefficient methods of heating your water for personal use. These coils work by circulating domestic water through a coil located inside the boiler which transfers heat from the boiler to the water. If there is any one single thing that will save fuel is to get rid of this old "side arm" heater. Ever notice your boiler firing for about a minute and then shutting down? Well, here's why. The temperature sensor that controls when the boiler fires is located in the center of this coil. So if you open a faucet to fill a pan of water, the cold water moving through the coil can trigger the boiler to fire. If the rest of the boiler is up to temperature it only takes a minute or so to churn the water and then shut down. This is wasted fuel. Keeping the boiler at +170 degrees (maybe as much as 20 gallons of water) to fill a quart pan of water is about as inefficient as you can get.
Indirect Domestic-Hot-Water Tanks
The FCX does not utilize a domestic coil. Instead it has a seperate unmixed circuit that takes water from the hotest part of the boiler for circulation through the coil within a DHW tank. This heats up the domestic water in the storage tank for later use. This tank is extremely well insulated so there is very little heat loss when there is no demand. This has become the standard of efficiency for all boilers today. An additional pump is required.
