Category Archives: Family

Span of control, in the shower.

One of the features in our new home is a well-balanced hot water system.  But it needed some tweaks….

In our old house we had two knobs, one for hot water and one for cold.  These knobs were attached to valves that controlled the water flow.  This is a very primitive technology akin to regulating the flow of water by kinking a garden hose. Which is fine for a garden hose, but when you mix hot water with cold water, like in the shower, you want a better method. To get an even temperature through your shower head you have to pinch the hose in just the right ratio.  This ratio is dependent upon many factors.

First is the relative temperature difference between the hot and cold water.  Also there is the difference relationship of this temperature to the desired shower temperature. And lastly you have to account for the pressure of the water in the piping.  The temperature difference between hot and cold does change, but normally over a long period of time unless you use the hot water faster than the water heater can recover.  The pressure in the pipes is the issue.

Anyone over 45 years old, or owns a house with old plumbing fixtures, knows how much fun it is to flush the toilet while someone else it taking a shower.  This was the state of control I was used to, until we bought our new house.

Our new house has pressure compensating valves.  A sudden drop in pressure has no effect on the output temperature of the water flow to the shower head.  There is a mechanism that actually changes the flow depending on the pressure, and restricts the maximum temperature.  Which is fine and good, but this functionality can cause control issues that require tweaking.

Shortly after we move in to our new home, I found that each shower was set differently.  I discovered this one day when I tried to take a hot bath in the guest bathroom.  The water would not get hot enough.  This was probably set to protect toddlers and such from scalding, thank a lawyer. On the other hand our master bathroom shower could be used to make coffee.  However it’s just me and my wife, and I want hot water in the guest bath and some control over the temperature in the master.

Time to get out some tools and experiment, but it turned out to be a bigger challenge than I thought.  After a web search on the brand of valve I found out how to adjust the maximum temperature.  Ok, the guest bathroom was done; bring your children over for a scalding.

Next project is to look into our shower in the master bath.  It was already hot as hell.  But trying to find the sweet spot where the water was not too hot, but not too cold was kind of touchy.  I have to tap the handle in tiny increments until the temp is just right.  So how do I open up the comfortable range without losing the top end heat?

To fix the problem I had to delve back to my control theory training.  One portion of this control loop was changed, but the source was not, namely the water heater setting.

I found that our water heater was set to “way hot”.  This is not an official setting; it goes from Vacation, to warm then A, B, C, and finally Very hot.  We were on C. So I changed the setting to A and let it sit until my morning shower.  150 degrees is too hot, but so is 130 degrees.  I can still have too hot if I lower the overall temp.

After I made the changes to both the shower valve and the water heater, the shower temperature control range looks like this:

Optimizing my shower control.

Optimizing my shower control.

The top image is the before condition.  Once adjusted it is closer to the bottom image.

Now that is more like it. Sure the too hot portion was cooler, but still too hot.  It simply opened up the comfortable span.   I now have much more control over the shower temperature.

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