Why not have the Indirect Water Heater on a Timer?
In the eighties, there was a big push on water heater blankets and timers for electric water heaters. They both went by the wayside now. I believe they may come back, at least the blanket insulation. I have an oil-fired water heater in my home, and I decided to put a timer on it as it is just my wife and me. I know a product that maintains a constant temperature and is connected to a chimney; the chimney will siphon heat throughout the day and night, so a timer made sense. I also know longer run times are better than shorter run times.
We use a little hot water in the morning M-F, and the majority in the PM before bed for showers. The dishes just get put into the dishwasher until it is full. On the weekend, we use most of the hot water on Saturdays for laundry and cleaning. Sunday in the AM and not again until Sunday evening. My wife is in the habit of taking her shower before prime-time TV, and I take mine before bed. Keep in mind that when the timer turns off, the water is not instantly cold. I start running out by the time I am getting out of the shower.
I had an old setback thermostat with a 5+1+1 capability. This means that Monday through Friday follow the same program, Saturday follows another, and Sunday follows yet another. I bought a Honeywell R8285D transformer relay and rigged a thermostat and relay for the water heater. I set the program on the thermostat to run from 7:00 AM to 9 AM, then shut it down. Turn back on from 6:00 PM to 11:00 PM, Monday through Friday. On Saturday, it ran from 8 AM to 9 PM. On Sunday, it will run from 8:00 AM to 9:00 AM and again from 6:00 PM to 9:00 PM. When the thermostat program calls, I have the thermostat set to 90F, which is higher than the basement temperatures it will ever see, as it only turns on the water heater. The off cycles, I have the thermostat set to go to 40F, which again it will never see.
I installed an hour meter on the water heater and cut the run time hours by 58%. I had it on the burner motor, so it only checked the burner run time. This was only a 2-week test. I believe this would be enough time to get a rough idea of my savings, as my lifestyle does not change significantly during the winter. In the summer, when we are away many weekends, I can keep the temperature low until we return, then start the run program. A timer may be a little harder to shut down during extended off periods unless you put a switch in the low-voltage wire to the timer. So, what about considering adding a timer to an indirect water heater?
I have given this some thought, and I think it would be a good idea if you could work around a certain schedule. The more hours it is off, the more fuel you will save. The results will vary depending on the size of the indirect water heater (IWH), the method of sizing, the average room temperature, and the piping configuration. The IWH must have the proper boiler water flow through it for maximum savings. The domestic side should be trapped as shown in the IWH proper piping page. A properly sized and piped water heater will reheat in less than 10 minutes to maintain temperature and around 20 minutes after a setback. Keep that in mind when deciding on the time to set. I am sure it may take a few tries to get things set properly. Most timers have a manual switch if needed. The pain is if you live in an area that changes time for daylight saving time, as you will need to reset the time twice a year.
Here is a simple wiring diagram for a Paragon. This is a timer similar to the one used on an electric water heater, but it will follow the same schedule every day, although you can set it to run multiple times a day. You may be able to find a small light timer with multiple timer settings, or use a cheap thermostat and an R8285D like I did. Here is a simple diagram for a Paragon or similar timer.
I would like to see feedback from those willing to try this and see how it affects the fuel consumption on their IWH. I cannot test it as I do not have an IWH nor a hydronic system in this house. I can supply wiring diagrams for other control applications if needed.
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