In the eighties there was a big push on water heater blankets and timers for electric hot water heaters. They both kinda went by the wayside now. I think they may come back, at least the blanket insulation. I have an oil fired water heater in my home and decided to put a timer on it as it is just my wife and I. I know a product that maintains temperature all the time and is connected to a chimney, the chimney will siphon heat all 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 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 M-F is the same program and Saturday is another and Sunday is yet another. I purchased an R8285D transformer relay and rigged thermostat and relay for the water heater. I set the program on the thermostat to run from 7 AM to 8:30 AM and shut down until 6 PM to 9 PM Monday through Friday. On Saturday it runs from 8 AM to 1PM and again from 6 PM to 9 PM. Sunday it will run from 8 AM to 9 AM and again 6 PM to 9 PM. When the thermostat program calls I have the thermostat set to 90ºf which it will never see basement temperatures that high as it only turns on the water heater. The off cycles I have the thermostat set to go to 40ºf 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 burner run time. This was only a 2 week test. I think that is enough to get a rough idea to savings as I lifestyle does not change that much during the winter. The summer we are gone many weekends so I can just hold the low temperature until we get home than just hit run program. A timer may be a little harder to shut down on extended off periods unless you put a switch in the low voltage wire to the timer. So what about the consideration of 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 can work around a certain schedule. The more hours it is off the more fuel you will save. The results will vary on the size of the indirect water heater (IWH), the way it was sized, average room temperature and the way it is piped. The IWH must have the proper 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 for maintaining temperature and around 20 minutes after setback. Keep that in mind when determining the time on setting. I am sure it may take a few tries to get things set properly. Most timers have a manual on switch if needed. The pain is if you live in an area that changes time for daylight savings 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 like you would put on an electric water heater but it will be the same schedule everyday although you can do 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 some 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.