Water Heater Temperature Setpoint 1

[TrippL]

In response to a closed thread inquiring to water heater setpoint: My rule of thumb for storage type water heater temperature setpoint depends on the use of the hot water.

Setpoint should be 140 deg F with master mix down or point of use mix down to 115-120 deg F.

Exception: Small systems with no showers can have setpoint at 120 deg F, except in medical facilities.

Reason: Legionella is a bacteria that is most commonly acquired through inhalation. If there are no showers and the system is small, then there is little chance for the inhalation of Legionella if somehow it manages to form in the system. However, there is always a chance of Legionella forming in temperatures 140 and below.

 

[MechEngNCPE]

You are correct sir! North Carolina Plumbing Code says you can't go over 140 for most applications (I think commercial and residential). I provide thermostatic mixing valves at all showers to temper down to 115 usually.

 

[m2e]

I actually have a question about this topic.

In a light industrial building, there is an emergency shower, a washroom with shower, a couple of hand sinks and a mop sink. The building is about 6000 sq.ft. so there's going to be a recirculation loop for the hot water. The fixtures are scattered around the single floor building, so it seems to be make sense to have a master mixing valve for the hot water to bring it down from 140F to 120F.

Can you have a recirculation pump and the mixing valve at the same time? I can't figure out where to put the pump and where to put the mixing valve.

 

[PEDARRIN2]

Depending on the plumbing code, you might be better off with circulating 140.

In the IPC, public hand washign facilities require a ASSE 1070 mixing valve at the sink. Since the design delta T across these tends to be ~10 F and you want 105 at the fixture, circulating 120 is not a good option since the 5 F delta T for the circ pump will put you pretty close.

So I would circulate 140 and put the 1070 at the washroom sinks. The shower sinks should be ok with the pressure balance, although a thermostatic would be safer. The emergency shower has to have a mixing valve and the mop basin can get 140.

If you still want to circulate 120, you will need the master mixing valve and recirc pump. The literature for the mixing valve often has a pipe diagram indicating the placement of the recirc pump. I use Symmons, Bradley, Lawler, Powers. They even manufacture a factory assembled unit that has the recirc pump already installed. I like these since, even with the diagram, the plumbers often still get it wrong.