What is this “T” device on my 2004 Hunter Water Heater

[Jennabird]

There is a “T” device on my water heater. What is it there for? Is this piece necessary when replacing the 6-gallon Kuuma water heater tank?

 

[dlochner]

My first thought was it looks like a tempering valve that mixes hot water from the tank with some cool water to prevent scalding. When the tank is heated by the engine the temperature can reach upwards of 160° F which will scald and cause serious burns. So, yes a tempering valve is good to have.

A second look and I'm not as certain. Where does the black hose go? That hose and probably the other black hose look like it has reached its end of life.

 

[jssailem]

It is attached to your hot water outlet. It appears to be an automatic anti-scalding valve. The image does not clearly show a cold water line attached to the valve. I suspect one of the black hoses goes to cold water. These valves come in many shapes and sizes.

If both cold water and hot water are attached that is my best guess. Yes you will want that valve on the new unit. It will protect the crew and guests from too hot water being supplied to the hot water taps on the boat.

 

[Jennabird]

Here is another photo from a different angle.

 

[Jennabird]

I’m being told this is a Thermostatic Mixing Valve. “Thanks Mike”
This particular one is no longer available.
I’m hoping when I pull this off the old water heater tank, it doesn’t get damaged.

 

[dlochner]

The valves aren't that expensive, replace it. No need to buy one from a marine store, your local big box hardware store will have them as well any plumbing supply store.

On most mixing valves there is a knob to adjust the temperature. In the first photo that knob isn't visible, is the black thing on the back in the second photo a knob?

 

[Jennabird]

It’s hard to get a camera into there. But it’s not a knob.

Here’s the basic explanation I got:
Thermostatic Mixing Valve, shuts off the Antifreeze (engine side) from going into the water tank when it senses the Hot Fresh water is getting too hot So it keeps the temperature of the water tank to about 120 degrees instead of 180 degrees

 

[dlochner]

It’s hard to get a camera into there. But it’s not a knob.

Here’s the basic explanation I got:
Thermostatic Mixing Valve, shuts off the Antifreeze (engine side) from going into the water tank when it senses the Hot Fresh water is getting too hot So it keeps the temperature of the water tank to about 120 degrees instead of 180 degrees

Kuuma does things a little different. The more common approach is to let the HW tank heat to 160° or whatever the engine temperature is and then mix cold water with the HW leaving the tank in mixing valve. This has a couple of advantages, heating the water to 160° kills anything living in the tank like bacteria and mold and it provides more hot water as the 160° water is diluted with cold water to bring the temp down to a safe level. in effect this allows a 6 gallon tank to provide about 8 gallons of hot water. (If I got the math right.)

 

[jssailem]

OK. Interesting. Same results, only limits the temperature in the tank, rather than letting the tank heat up to engine temp and adjusting the water temp flowing out by mixing in cold water.