Looking for ideas

[Dafunktyfunk]

Had an idea to install a Z-wave duplex receptacle outlet in the place where my gas hot water heater (120V only powers thermo and blower) is. Basically a way to control when the water heater heats or doesn't.

I was thinking to have HS turn the plug off at night when people are in bed or when we run the Bedtime event. THen have it turn power back on an hour or so before we wake up.

Part 2 is to have the water heater turn off when we leave the house and then back on about an hour before we come back from work or even later. Here are my questions:

1) Anyone see and pros and cons to this?

2) Anyone else doing this already with good results? Or bad...

3) Suggestions on timing the on and off, something I am over looking?

Any feedback would be good.

The goal behind this automation is to prevent the hot water heater heating water when no one wants it. It would stay pretty hot as it is well insulated. The savings in the winter could be good, not so much in the summer when the nights are warm anyway.

[Uncle Michael]

I'm assuming this is a dedicated heater for domestic hot water. Have you confirmed that the heater stops heating the water when you disconnect the power? Our gas water heater heats the water independently of whether the power is on or off.

As you say, the water heater is insulated, so it's not clear how much you'd save. Also, if it's in a heated space, the "waste" heat goes to heat the house as a whole, so the reduction in gas use in the winter will be at least partially offset by additional heating load on your furnace.

If it's in an unheated space, it may be more cost effective to increase the insulation around the water tank to reduce the heat loss.

[Dafunktyfunk]

The water heater is in the garage and is in unconditioned space. The thermostat is electric so when there is no power, the heater does not heat.

It would be very easy to install an outlet but I thought I would ping you guys hear to get feedback.

[rmasonjr]

I read somewhere a long time back that it would take longer to heat a full tank of cold water than to keep it heated with shorter cycles between. I have no data to support this; I just remember reading something along those lines...

[Uncle Michael]

Thermodynamics would support the notion that allowing the tank of water to cool will save energy because the loss of energy will be proportional to the difference in temperature between the water in the tank and the outside surface of the tank. So, the colder the water, the less energy will be lost. On the other hand, gas water heaters are not as efficient at electric heaters (it's the relatively lower cost of gas that makes them more cost effective), so the energy lost to reheat the water may exceed the energy that was saved by letting the water cool.

There must be data somewhere on that topic, but I have no idea how to find it, and even if I did, it's not clear how relevant it would be to your exact situation. Given that you are keen to try it, why not do the experiment? Take careful measurements of your gas consumption with the thermostat powered 24/7, then introduce a period where you power down during part of the day and compare. (If you want to be more accurate, repeat each condition several times.) Let us know what you learn.