Electric water heater with timer and thermostatic mixing valve

pinkeng

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Aug 5, 2021
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northern california
Makes sense. I assume you added external insulation around the sides and top. One other thing to reduce heat loss if the distribution piping is above the water heater is to put a U bend in the hot water supply. If your hot supply pipe is hot above the water heater you can/ will lose heat that way. Adding a 12" drop and then back up will prevent thermosyphon. Hot water is less dense so it rises to the top. A 12" deep/ long U or S bend stops that. Just FYI.
 

SolarPrep

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Jul 15, 2021
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Just a couple of comments to add to this old thread:

Here in the Midwest, we have a lot of limestone, and very hard water. That limes up water heaters over time. We do 2 stage filtering of all water coming in the house, except for toilets, and outside spigots. I do run toilets through a separate mineral filter.

We use the 20" orange colored housings (high temperature filters) on boilers, solar water tanks, water heaters, etc with a cheap pump and either a timer to turn it on, or just a manual switch. Cycling it periodically helps keep the fluids clean, and prolongs life of all devices.

Use a watt meter to check how much current is used by those old fashioned mechanical timers.

I've seen people scrounge a cheap or free tank, and hook it up just to let water come up to temp of the house, before going into the water heater. Our ground water is about 50 degrees here, but I have no way of ascertaining if it absorbs more heat from the house, than it saves from heating that same water up with your water heater. I suspect it does save energy.

If you are shopping for a three way valve for any device, check the specs for pressure drop through the valve. I used to use Honeywell, but switched to Caleffi after realizing how much extra energy it requires, especially if you are pumping water. If it is just City pressure it may not make a difference.

A small pump on a hot water recirculation loop does save energy in most cases. I picked up a brand new bronze TACO pump at a local thrift shop for $10 that is 1/40th hp. Perfect.

Insulate all tanks. Pay attention to piping insulation.

Consider building a hot water drain heat exchanger with scrap parts, and hook it up to things like showers. Source material through a local scrap yard, and check out designs on "Build it Solar".
 

12VoltInstalls

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I have no way of ascertaining if it absorbs more heat from the house, than it saves from heating that same water up with your water heater. I suspect it does save energy.
Energy savings is a wash in winter heating regions.
Dollar savings comes down to what you heat the living space with: if the water heater is electric, generally electricity costs more per BTU in most locales than other energy sources. Energy costs from least cost to most cost per BTU is usually coal, wood, wood pellets, oil, propane, with electricity the highest (in many regions electric heat is not much more costly than propane). (Natural gas is a ‘flyer’ as some regions the cost is very low while in others it is higher in cost/BTU than oil. Electricity in some places close to hydro plants electricity is cheaper by a lot. So ymmv)

In summer, pre-warming water ahead of the water heater is cost-free, while in winter the dollar savings will be whatever the difference between your heating fuel cost and hot water heater fuel cost is, per BTU, if any.
 

magic8192

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Feb 26, 2021
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I have a few comments about using a hot water heater with 180 degree thermostat, a mechanical timer, and a mixing valve.
The things I have changed since originally hooking it up. I put scald guards on the showers so the kids don't accidentally get hurt if something goes wrong. I originally wired the timer to the lower thermostat. I changed that and wired it up to the upper thermostat and it now controls both thermostats. You have to change both thermostats anyway because I originally only changed the bottom and the top thermostat would trip on high temp.

This is the biggest energy saver I have done. I averaged about a 20% drop in my power bill with this. I have a 50 gallon tank and I have enough hot water to stay above 120F for 2 days with the normal showers/dishwasher runs.
 

SolarPrep

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Jul 15, 2021
Messages
121
Energy savings is a wash in winter heating regions.
Dollar savings comes down to what you heat the living space with: if the water heater is electric, generally electricity costs more per BTU in most locales than other energy sources. Energy costs from least cost to most cost per BTU is usually coal, wood, wood pellets, oil, propane, with electricity the highest (in many regions electric heat is not much more costly than propane). (Natural gas is a ‘flyer’ as some regions the cost is very low while in others it is higher in cost/BTU than oil. Electricity in some places close to hydro plants electricity is cheaper by a lot. So ymmv)

In summer, pre-warming water ahead of the water heater is cost-free, while in winter the dollar savings will be whatever the difference between your heating fuel cost and hot water heater fuel cost is, per BTU, if any.
12voltInstalls: I would assume that your comment is accurate. I didn't refer to my own situation, because our hot water is via integrated heat exchanger off gas boiler, with additional solar hot water panels. It seems bizarre to be considering going back to electric, based off PV, but right now it looks like gas prices are going to take a serious hike upwards.

If I was building a new home today, I would build smaller, and super energy efficient. Lots of PV.
 

Hedges

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Mar 28, 2020
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Mechanical timer - to turn off during peak rate hours, and that's the savings on bill?
Following a power failure you have to adjust time or would operate during wrong hours.

I got some Harbor Freight digital timers. They have a rechargeable battery.
They are for 120V and light weight. Used to use for espresso machine, but failed so now use mechanical. I do use one for an electric water heater that is running on 120V rather than 240V. Power relay would be needed for 240V or higher wattage.

It seems bizarre to be considering going back to electric, based off PV, but right now it looks like gas prices are going to take a serious hike upwards.

How about picking up an electric water heater and plumbing it as a pre-heater or post-heater? Last one in line has to maintain temperature.
Could enable electric heating when gas prices rise, or when producing surplus electricity that doesn't get good net-metering credit, or during low-rate times.

Ideally would have a single tank with both heat sources. If gas + electric, that would have gas flue as a heat-loss path. Since yours is heat exchanger, might be able to plumb a heating element into pipe, optionally enabled while pump running.
 
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