DHW

[huffdawg]

Do most Indirect Hot Water heaters get plumbed with a thermostactic mixing valve on the domestic side.

Thanx Huff

 

[bpirger]

Mine isn't...and I've never seen one done that way (I've seen about 5 indirect tanks in my lifetime!) In fact, I've never seen any DHW tank with a mixing valve on the output side, though I have only seen maybe 20 of these in my lifetime... But there was a thread over the summer where this was discussed a bit and was reportedly becoming required by code in many areas, and maybe already so up North of the border.

The discussion stemmed around my desire to lower my tank aquastat setting so I could heat my DHW with lower Garn water temps....to burn every four days instead of three. There was concern about Legionares's and other problems in the tank....though I never had it over 120 anyways, and have never had a problem....

 

[cheapsx]

I did mine that way because it is undersized for the household. By heating water to 140* it stretches the hot water out, or makes it act like it's larger than it really is.

 

[skfire]

I did mine that way and most new ones are done this way now, in these parts(Closer to NYC).

SK

 

[huffdawg]

In the directions for my smart 40 it was showing a mixing valve . the Indirect tank in my house doesn't have one either. I guess the aquastat keeps it @ 140

Cheers Huff

 

[Humplumb]

No most don't get a mixing valve they have a thermostat to control water temp.Which does exactly what a
Mixing valve does controls water temp.Only reason would be if you were undersized like Cheapsx said. Then your raising the water
Temp higher to give yourself a larger dhw load.

 

[ewdudley]

No most don't get a mixing valve they have a thermostat to control water temp. Which does exactly what a Mixing valve does controls water temp.Only reason would be if you were undersized like Cheapsx said. Then your raising the water Temp higher to give yourself a larger dhw load.

Some may prefer not to assume that the control can never fail on, or that the zone valve can never fail open.

 

[maple1]

I think a setup that could allow a ghost flow of hot water thru the indirect tank coils when the boiler is hot, together with a mixing valve for DWH output, would be something to consider. That way the tank could be allowed to 'overheat' without worrying about scalding someone at the tap, basically increasing the BTU capacity of the tank for free (no thermostat or zone valve or circ pump for that). Then when the tank does get too cool, the thermostat would kick on a circ pump, if needed. I think with a setup like that, I could go all heat season just heating my DHW with ghost flow. Sorting out the plumbing for that might be another story.

Having said that, I use to have a mixing valve on my furnace DWH coils, but it stopped working (forget if it bypassed too much cold or none), so I replaced it with a ball valve that I close in the summer so I could run cooler boiler temps.

 

[Fred61]

Although I don't keep up with plumbing codes, it was my understanding that all indirect and electric water heaters were to be kept at 140 plus, requiring a mixing valve on the output. Apparently the 120 degree temperature isn't high enough to ward off Legionella bacteria. I remember that at the time I was being told of the new or proposed code, the only thing that was going through my head was: "how am I going to get around this?"

A former co-worker who had lost his wife and was living alone, developed Legionnaire's disease a couple years ago and it was attributed to low hot water settings with minimal use. His system has since been re-plumbed with the mixing valve and set at a higher temperature. I suppose that with enough use, the bacteria would not grow at the lower settings.

 

[mikefrommaine]

No most don't get a mixing valve they have a thermostat to control water temp. Which does exactly what a Mixing valve does controls water temp.Only reason would be if you were undersized like Cheapsx said. Then your raising the water Temp higher to give yourself a larger dhw load.

Some may prefer not to assume that the control can never fail on, or that the zone valve can never fail open.

I had my aquastat fail recently. It was stuck on. Woke up to dhw that was at 180 degrees. Might not have noticed right away if I had a tempering valve.

 

[huffdawg]

I work on a passenger ship in the engineroom, we have a tempering valve on the domestic side its set @ 120 °F . I have mentioned legionaires numerous times to the powers that be and they are more concerned about scalding and lawsuits. They are too cheap to spend the $500 per valve on the 120 showers on board . Then they could set the tempering valve @ 140 °F and solve both problems.
Having said that, no one has come down with legionaires for as long as I can remember.Maybe because the water isnt staying still for long. The funny thing is that they have anti scald valves in the 4 luxery suites on board. They know the customers with money enough for a luxery suite have money to sue.

Huff

 

[maple1]

I think the legionaires worry is on the storage side of things, ie. before the tempering valve. So if it's kept 140 or higher, it'll kill the germs & not scald. I think.

 

[huffdawg]

Toddlers and young children are at the highest risk of being scalded by hot water. It is easy to receive third degree burns from exposure to hot tap water, which comes from not only hot drinks and pots cooking on the stove, but from bath water. An approximate one-second exposure to 160° F water will result in third degree burns.1 Where the water is 130° F, an approximate half-minute exposure will result in third degree burns.2 This is the reason that the Consumer Product Safety Commission suggests that water heaters be set to a maximum temperature of 120° F, even though an approximate ten minute expsoure to water heated to this temperature can result in third degree burns

 

[MasonWoods]

I have never used mixing valves on DHW heaters on the out-going side. I always set my tank temperature to what was comfortable. Never considered the bacteria.

It's now got me re-thinking it though. I have a DHW coil in my unpressurized tank that preheats the water going into my DHW electric 40 gallon tank. I put a mixing valve in the line before the electric tank to keep it from feeding in at the high temp. Maybe I should yank that mixing valve out an just put it on the outlet of the 40 gallon electric tank? Hmm

 

[bpirger]

https://www.hearth.com/econtent/index.php/forums/viewthread/76948/

There's the thread from this summer with more good content about DHW temp vs. critters....

 

[Clarkbug]

Most of the folks around here who run a sidearm on their electric hot water heater connected to an always circulating OWB put a tempering valve on the hot water heater outlet. The potential to have 180 degrees at the tap is not a good one.

If you have a zone control that regulates the temp going to your indirect, no need to temper it. If you just always run your boiler water through a sidearm, temper it.

 

[SmokeEater]

I'm a newby at this hydronic heating, radiant heating, and indirect DHW, and will continue to read, discuss, and learn the hows and whys of this science. The results of this has led me to design my own system based on the teachings of all of the wizened contributors of these forums. My plan is to connect my two boilers, one pellet and one oil, to the same large buffer tank, really a large indirect DHW tank, raise the temp of that water to 180 or better, if I can, and take some of that hot water and mix it with an ASSE 1017 thermostatic mixing valve to supply 120 degree water to the house. No scalding and no legionnaires. The rest of the water will be pumped through a flat plate HX to supply the hydronic and radiant portions to heat the home. That ASSE valve is designed to stop hot water flowing if it can't mix to lower the temp to the preset temp.