Water system mixing valves

[buswarrior]

Hello busnuts.

Those of us who use hydronic heaters and/or engine heat through a heat exchanger to heat your plumbing hot water have a safety issue:

The water gets VERY hot, typically much higher than a domestic hot water heater.

In order to avoid scalding the kids, the navigator, or yourself, proudly install a mixing valve to automatically blend cold water in with that extremely hot water to get the temp down to safer levels at the tap.

Here's one source I stumbled on, $100 - $130, that lists Honeywell mixing valves with a variety of plumbing style connections, there are many other sources of supply, this one is for illustration purposes:

http://www.suremarineservice.com/everhot-tankless-on-demand-copper-water-heater.aspx

In our busnut brilliance and efficiency, we do have occasional lapses in safe execution?

happy coaching!
buswarrior

[daddysgirl]

I would love to be included in this safety warning.
However, I do not have a system that uses the engine to heat the water. I would LOVE more details??

Also, I was actually dreaming last night about a system that captures some of the engine heat and distributes it for additional OTR heat for those who have removed their stock heat/AC systems. Mine is still in place and fully functional... dreams are strange.

[Oonrahnjay]

... However, I do not have a system that uses the engine to heat the water. I would LOVE more details??  ...

      My Attwood water heater has what they call a heat exchanger coil in the heater itself.  It's hooked up to the engine coolant/radiator system.  As BW says, the water in the heater gets *very* hot.  This unit is equipped with called a tempering valve; it automatically takes the water in the tank (no matter if it was heated by the exchanger or the 120V element, or the propane burner -- it has all three) and automatically mixes hot and cold water so that the output hot water is always a set, safe temperature.
      Before I ever used my unit, I was talking to Gary Throneberry ("Garhawk" on here) about a system like this.  He showed me the setup on a GM motorhome from the think the early 70's.  That "heat exchanger" was two pipes about 3/4"; one in a loop off the radiator and one the feed into the water heater tank.  The two pipes were just stuck together with clamps in a section that couldn't have been more than a foot or 14" long -- Gary said that it would heat water in just a few minutes of running the engine.

      DG, there are components available that do exactly like you want.  I can only guess how to Google but I suppose it might be something like "motorhome water heat exchangers".  Some of them take the hot antifreeze from the engine/radiator into an exchanger manifold that sends heat to the water heater and also other circuits to run radiators (or "radiant heat" as BW is using) to heat the bus interior.  And, yes, you'll need a mixing or tempering valve for the convenience of constant temperature domestic hot water and the safety of that water.  (I'm guessing that in an interior heating system, you want the heated water/antifreeze in that system to be as hot as possible and you'd regulate that system by other means. 

[daddysgirl]

Thanks Bruce...and BW for the link.
I bookmarked a few pages so I can look into ordering one when I re-build the interior of the Green Machine. My hot water heater is 16 years old, propane and located in a terrible place. I lost the argument with dad when we started, so this is awesome

[Scott & Heather]

It's not complicated. We have an $80 watts mixing valve that doesn't allow water beyond 118°F to come through to the house hot supply. Our water heater Tstats are both set to 150°F. Take a 40 gallon tank full of 150°F water and when you mix it down to a comfy shower of maybe 105°F, you get a long long hot shower. Those valves are at Home Depot btw. Nothing fancy or special about them.


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[TomC]

One more KISS item I do-I only use two-10gal electric water heaters. One plumbed into the next with the final running through the inverter for hot water going down the road. No heat exchanger, no Diesel fuel fired heater, no water pumps (in the hot water), no ignitor problems. I can run the gen in the morning for two hours to charge the batteries and have hot water all day and night. Just my way. Good Luck, TomC

[sixtyseven]

the final running through the inverter

Did you mean through the heat exchanger.....or do you actually have some way to exchange heat from your inverter ?

[TomC]

More accurately I should have said that the final water heater is WIRED through the inverter so I get hot water going down the road from the big 50DN alternator. Good Luck, TomC

[sixtyseven]

Oh,  after rereading your post that makes perfect sense.   It was the word "plumbed" that threw me.

[Seangie]

Don't forget to put a check valve on the cold water feed to the hot water tank.  Otherwise the cold water will be hot water too and mixing valve won't matter at that point.

We have a 20 gallon hot water tank that is heated by the engine.  With the mixing valve its like having 30-35 gallons of hot water.  Nice long showers.  Its pretty quick recovery heating up as well.  The marine tanks seem to recover quicker than a household tank.

-Sean