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Advantages and disadvantages of mixing valve

How to save Hot water using a mixing valve

How does mixing valve save hot water?
Remember, a mixing valve is exactly what you do during shower ... you add cold water to hot.
Each faucet; bath, kitchen, shower and tub faucet is a mixing valve... where you manually adjust water temperature by adding cold
Each time hot tap is turned on, new cold water immediately enters bottom of water heater as hot water leaves top of tank going to shower..
When you use mixing valve located at water heater instead of mixing valve located at shower, then you save the amount of hot water that travels down the pipe going to shower.
How much hot water is saved?
Every 10 feet of 1/2 pipe holds .12 gallons of water.
If bathroom is 20 feet away. 3 showers per day .72 gallons per day x 365 days = 262 gallons of cold water that does not enter tank.
That means 262 gallons of cold water is not heated to thermostat set point.
The math can be more complex than this 2-D example. But a mixing valve keeps more cold water out of tank, and water heater stays hotter
Adding mixing valve is required for solar water heater. Because sipping Hot is important strategy for preserving the solar heat stored inside water heater.
Rule of thumb... if it's good strategy for solar... then it's a good strategy for regular tank too.
Water heater is energy battery. Don't drain the battery.
Mixing valve
Mixing valve adds cold water to hot line so water temperature remains constant.

1) This lets you heat tank full of very hot water during good solar days if you use solar heating.
2) This lets you heat full tank of hot water during low peak pricing periods overnight.
3) This lets you send very hot water to washing machine on separate water line, and send tempered hot water to other water line going to faucets and kids bathroom.

Mixing device kit

Kit has more features/ scroll down for mixing valve without kit

I run my water heater upper and lower thermostats at max (150F they are NOT heavy duty 170F thermostats). See thermostats
I have my mixing valve set so I get 112F water (my preference) on the hot side at the kitchen tap.    

Without a mixing valve I would have to set my thermos at 110F instead of 150F.  Because I have a higher setting on my thermostats I can store the excess energy from a sunny day (solar heat), or store excess heat from low electric price.
The water heater stores energy. .. basically the extra BTU it takes to heat the water from 112F -> 150F).  
I think my calculations are that my 105 gallon water heater can store the equivalent of 150 (or more) gallon water heater depending on the incoming cold temp (time of year related). 

With the mixing valve my water heater stores about 20-25KWh of energy.

Do you have a mixing valve in your setup?

Buy from my affiliate links:
Mixing valve kit at Amazon
Water heater mixing valves at Amazon

Resource:
Mixing valve .pdf
di-electric nipples

Use di-electric nipples for connections at top of water heater

Di-electric nipples help prevent corrosion at water pipe connections
Di-electric nipples are good replacement for factory-installed heat trap nipple that might cause clogs and noise
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Di-electric nipples
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Mixing valve kit
Larger image

Mixing valve kit installed on top of tank

This installation shows standard gas or electric water heater
Mixing valve kit installed on top of tank
5 total ports for connections

Laundry/ washing machine / receives very hot water
Sinks and bathtubs receive tempered water at lower temperature

Mixing valve has a thermostatic setting knob
Mixing valve automatically releases cold water into the water going to sink
The cold water reduces temperature of water that travels to sink
Buy from my affiliate links:
Mixing valve kit at Amazon
Water heater mixing valves at Amazon

Resource:
Mixing valve .pdf
mixing valve Mixing valve
Temperature gauge
Permanent install on hot pipe leaving water heater.

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Winters Temperature gauge

Advantages of Mixing Valve:


1) Increased hot water storage capacity.  Instead of replacing a good working water heater with a bigger one that costs more and takes up more space, add a mixing valve and turn up the thermostats.  Works with Gas or Electric water heaters.

2) After 2015/04, electric residential water heaters bigger than 55 gallons will not longer be inexpensive and easy to install.  A mixing valve will help you fill that garden tub without the hassle and expense of an electric heat pump water heater.

3) Perfect for thermal or photovoltaic solar hot water heating because of increase in storage capacity.  More capacity is always better.  Instead of just throwing away the excess energy, store it in the tank for a cloudy day.

4) Bacteria that causes legionnaires disease can grow in a water heater at a temperature between 68 and 122F.  Inhaling the bacteria laden hot water steam in a shower is the worst thing you can do with it.  Bathing and hand washing dishes is less of a hazard.  Very hot water will kill this bacteria.   The length of time it takes depends on the temperature of the water in the water heater.  


* 70 to 80 C (158 to 176 F): Disinfection range
* At 66 C (151 F): Legionellae die within 2 minutes
* At 60 C (140 F): Legionellae die within 32 minutes
* At 55 C (131 F): Legionellae die within 5 to 6 hours
* Above 50 C (122 F): They can survive but do not multiply
* 35 to 46 C (95 to 115 F): Ideal growth range
* 20 to 50 C (68 to 122 F): Legionellae growth range
* Below 20 C (68 F): Legionellae can survive but are dormant

5) Very hot water can also quickly scald skin.  Children and the elderly can have reduced reaction times, delicate skin and can get very badly scalded by hot tap water.   65% of all hospitalized burn-related injuries in children under 4 years old are directly related to dangerously hot tap water in residences.  
A mixing valve can make tap temperatures safe even when running a water heater at maximum temperatures.

6) Convert electric water heater from 240 volts to 120 volts so the elements run at 1/4 wattage and last forever.  Use mixing valve to increase storage capacity so you do not notice the massive decrease in hot water recovery rate.

7) Some mixing valves like the Honeywell kit have bonus connections for hot water recirculation kits and untempered hot water for cloths washer and dishwasher.
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8) The dial that moderates the temperature of the tempered hot water on a mixing valve is much easier to adjust than the thermostats on an electric water heater.   This makes fine tuning temperature at the tap simple and easy.  Possible to temporarily increase water temperature for a short task and then put it back back down when done.

9) The dial the moderates the temperature of the tempered hot water on a mixing valve INSTANTLY changes the temperature coming out of the water heater.   Changing thermostat settings requires time for the water heater to heat the water up to the new setting or lose enough heat with water usage or stand-by loss to reduce temperature.

10) Mixing valves *may* be better regulation of the temperature of the hot water at the tap compared to thermostats that kick water heating on and off.  Depends on quality of mixing valve and thermostats.
Honeywell mixing device

Honeywell mixing device/ valve only

Simple mixing device can be added at water heater or under sink
This can solve problem of uneven hot water arriving at tap
Children can be protected from scalding at their bath or faucet
Honeywell mixing device    

Buy:
Water heater mixing valves at Amazon
Mixing valve

Mixing valve installed with pipes

This installation shows example gas water heater
Mixing valve installed to side of tank

Laundry/ washing machine / receives very hot water
Sinks and bathtubs receive tempered water at lower temperature

Mixing valve has a thermostatic setting knob
Mixing valve automatically releases cold water into the water going to sink
The cold water reduces temperature of water that travels to sink

Disadvantages of Mixing Valve:


1) Running water heater at increased water temperatures may cause increased amount of calcification to precipitate out of the water requiring more frequent cleaning and shorter element life.
Depends a lot on water quality, hardness, temperature settings, etc.

2) Increased water temperature in tank will mean more stand-by loss.  However, it may not be as bad as a larger equivalent size tank which has greater surface area to lose heat through.

2) Increased installation space.  The Honeywell kit installs right on top of the tank hot and cold connections increasing installation height by several inches.
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