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Time of Day water heating with 24-hour electronic clock and 60-min timers

Time of Day water heating with 24-hour electronic clock and 60-min timers

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  #1  
Old 01-23-21, 08:32 PM
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Time of Day water heating with 24-hour electronic clock and 60-min timers

Please comment on whether our design is code. Is there a better solution? I had not heard of programmable water heaters but our solution is probably much cheaper.

Is it code to heat only part of the tank and leave it off most of the time?

The electric company off-peak hours are 7 pm to 11 am and weekends. On-peak rates are much higher in summer (June to September) and somewhat higher the rest of the year. Geothermal rate, which charges an extra $2/month, for both heat and hot water, also attic fan.

We designed our own time-of-day water heater setup with a cheap 24-hour 120V clock that only lets the water heater go on during off-peak hours. During off-peak hours you can either toggle the heater on with a regular switch (120V) or use a bathroom-located 60-min mechanical timer (GE, $6.50 with shipping from ebay, cheaper by the dozen). During heating season (for us about Nov-Mar) we want the tank to be full of hot water, otherwise only heat when needed. Plan ahead by turning the timer. You can also plan to use it every morning at 7, or every evening at 7, etc.

We have a 40 gal electric tank with two 4500W elements. When the tank is cold, the top element comes on first and once it reaches a certain temperature (120F) it goes off and the bottom element comes on. From cold to full tank is up to 90 min, which is 60 min plus 30 min., or toggle it on and remember to toggle it back off. There are also GE 60 min timers with ON settings.

In a Michigan January, it took 25 min for the top element to go off, as shown by a relay and light. We also measured temperature in the water heater with an indoor-outdoor thermometer. It was 50 and went up to 80 then we forgot to watch.

25 min is more than adequate for a long hot shower at 0.5 gpm with cold mixed in. For a longer shower or 1.5 gpm set it to over 120F. Winter groundwater is 50F and summer about 70F so set it shorter in summer (or use heated water from a black rainbarrel).

We need 3-wire 10-3 cable to run both the heater and the relay/solenoid which is connected to the 120V timer circuit. Or low-voltage solenoid and 24-hour timer. The 120 V ones were cheap.

We are building a highly insulated house (9" fiberglass in walls, 15" in ceiling). The water heater will run from about 9 to 11 am and then release heat all day. It could be set to go on again in the evening but we rarely use hot water. Cold dish and laundry washing and we shower or bathe once a week. The goal is to minimize energy use. So far the house cost $43 for electric heat (plus 20% because we pay for 100% renewable energy) from mid Dec to mid Jan and it gets into the teens at night here. No other electricity is being used yet. If we used electricity like typical Americans we might not need to add any other heat than the hot water (if that). We will also have solar heat from two south porches.

Our current house uses twice the electricity (all of which goes into heat), with insulation added to the 1939 walls and the roof and several layers of window glazing and insulating shades. It also stays cool in summer (we cook outdoors).

 

Last edited by PJmax; 01-25-21 at 08:03 PM. Reason: posted pic from member link
  #2  
Old 01-23-21, 08:49 PM
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Welcome to the forums.

Your design looks sound. It appears safe. As long as it's done to code you should be fine.
I'm not aware of any code that states what the water temperature must be. The link below discusses water temperatures but the only part that may affect you is maintained minimum water temperature and bacteria growth.

Hot water system temperatures
 

Last edited by PJmax; 01-25-21 at 08:30 PM.
 

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