Cold Shower Question

[Allie]

I am trying to diagnose our chronically cold shower problem.  Every morning, my husband gets up and gets ready for work and there is never enough hot water coming to the shower.  Before we pay a plumber to come out and try to figure out why, I thought I would ask you guys.  Here were the facts:

- In the morning, the first shower is cool.  The second shower is nice and toasty. 
- The bathroom is at the end of an insanely long length of pipe...easily 60 feet.
- The hot water heater was just repaired and is in perfect working order.
- The hot water heater has a mixing valve.
- The run from the water heater to the bathroom has an in line tank thing at about half way.  I assume it is for pressure?
- Some days the showers are very cold.  Some days they are ok. 
- My shower, the second one, is always fine...even if the end of his shower is cool. 

What is going on?  Other than the obvious, is there anything we can do to make this more comfortable, not waste a ton of water waiting for it to warm up, not waste a ton of gas heating the water up really hot? 

Maybe this is a stupid question, but I figured I'd ask if there was something we could do or some part of the system that makes the first shower so cool for so long.  The mixing valve was mentioned by the guy who just fixed our hot water heater.  My husband is convinced it's the in line tank.  Any ideas?

[Mtngrl]

Our master bath is at the furthest point in the house from our boiler, so we installed a hot-water recirculating pump under the vanity. Before we take a shower, we hit the button and the pump recirculates the water until it's hot -- then we take our shower. No wasted water, and the electricity used is minimal.

[GuitarStv]

Interior water pipes are typically 1/2 inch to 3/4 inch (.13 - .19 cm) in diameter.  Let's assume that they're a millimeter thick, that means that you've got an interior circle from .11 - .17 cm in diameter.  Pi are squared, so you're looking at an area of 0.037994 - 0.090746 cm^2.  You're claiming 60 ft
(1828.8 cm) of pipe.  That means that you're talking about 69.483 - 165.96 cm^3 of water.

That means you're going to have to waste 0.018 - 0.044 gallons of cold pipe water before the hot water from the heater actually makes it to your tub.

Now, we know that residential showers have a flow rate of 1.5 - 3 gallons per minute (https://articles.extension.org/pages/44367/what-is-the-water-flow-rate-to-most-fixtures-in-my-house).  That means that you should run straight hot water from your shower for 1.6 - .8 seconds before the hot water from the heater actually starts to reach your shower.


So you should be getting hot water from the heater really quickly.  It's possible that the cooler pipe is making your water cold before it hits the shower though.  Sadly, I can't remember the heat transfer equations to  calculate change of heat over time from a flowing liquid in a pipe to tell you exactly how many seconds that process would take.  My engineering degree was useless.  :S

[Allie]

Thanks!  We can take a shower for 15 min and it stays cool...then the water is turned off for a little while and the next shower is warm.  Maybe a recirculating pump will help.  Any ideas about effect of the in line tank thing or water heater mixer?

[Beach_Bound]

I know you said the water heater was just repaired, but this sounds like a water heater problem. The water cools over night (this shouldn't happen), then your husband takes a cold shower in the morning. The water heater comes on during his shower, and the water warms up between his shower and yours. His shower never gets warm because the water he's drawing from the heater is replaced with cold water.

You can try running hot water from a different faucet before his shower, preferably one close to the water heater. If it gives cool water after running for a few minutes, the water heater is definitely the problem. If water from that faucet is hot, then check the inline tank. Can you reach the inlet and outlet pipes? Feel them to see if they're warm or cool before and after both showers.

As a side note, I agree with GuitarStv's conclusion - it shouldn't take that long for hot water to reach your shower - but the math is a little off. 1/2 inch = 1.3 cm, not 0.13 cm. There's 0.5 - 1.2 gallons of cold water in the pipe, which still takes <1 minute to reach your shower. I'm also not going to touch any heat transfer equations :)

[GuitarStv]

I know you said the water heater was just repaired, but this sounds like a water heater problem. The water cools over night (this shouldn't happen), then your husband takes a cold shower in the morning. The water heater comes on during his shower, and the water warms up between his shower and yours. His shower never gets warm because the water he's drawing from the heater is replaced with cold water.

You can try running hot water from a different faucet before his shower, preferably one close to the water heater. If it gives cool water after running for a few minutes, the water heater is definitely the problem. If water from that faucet is hot, then check the inline tank. Can you reach the inlet and outlet pipes? Feel them to see if they're warm or cool before and after both showers.

As a side note, I agree with GuitarStv's conclusion - it shouldn't take that long for hot water to reach your shower - but the math is a little off. 1/2 inch = 1.3 cm, not 0.13 cm. There's 0.5 - 1.2 gallons of cold water in the pipe, which still takes <1 minute to reach your shower. I'm also not going to touch any heat transfer equations :)

Gah.  Screwed by Imperial yet again.

[jpdx]

Allie, I would like to hear more about this in-line tank. Is this an expansion tank? AFAIK this should be installed on a cold water pipe, not a hot, so double check that.

60ft seems like a really long run. As others mentioned your pipes are either 1/2" or 3/4" -- the latter will take longer for the hot water to reach you because there is so much more volume in the pipe. Would it make sense to relocate the water heater closer to the bathroom? Or install a dedicated tank or on demand heater just for the bathroom?

[Allie]

We can't move the water heater.  It is located in the garage, which is on one side the our house, the bathroom is on the exact opposite side of the house.  The line goes out the hot water tank, down into the crawl space, under the house, and back up.  It supplies two bathrooms on the far side of the house, neither of which get hot water quick.  The bathroom and kitchen that are right against the garage wall instantly have insanely hot water.  The master bath shower is chronically cold as two of the tiled walls (although not the one that holds the plumbing) are exterior walls, which get freaking cold in winter in Alaska*. 

The in line tank is about half way between the water heater and the bathrooms under the house in the crawl space.  It's not attached to the cold water line going into the house, so I don't think it's an expansion tank.  But, it is possible that someone thought, "hey, let's put the expansion tank along the hot water run to the distant bathrooms cause we ran out of room in the garage!"  We don't know who installed the tank or why.  We just assumed it was to ensure decent pressure to the distant bathrooms. 

* our house was built in the 90s and seems to be an attempt at grandeur without a lot of thought or money being put into it.  Really, who cares if the bathroom is big enough to count as another bedroom if it's 50 degrees all winter long?  Both the plumbing and heating ducts lose all heat before they get to the far side of the house.

[ysette9]

Are the pipes insulated under the house? Can they be if they aren’t already?

[jpdx]

Based on your layout, seems like the solution would be to install a second, smaller water heater (can be tankless) for that side of the house. I know, not easy or cheap, since you would need to redo some plumbing and also add gas and ventilation or an electric circuit.

Not sure about that mystery tank. Assuming it's an expansion tank, I read that its ideally recommended that its installed on the cold line, but I'm not sure why, and can be anywhere in the line even far from the tank. BTW expansion tanks don't increase pressure, they decrease pressure as the hot water expands.

I just read that you said the shower can stay cool for 15min. Hmmm. Even a 60ft run can't explain that. Now I am beginning to suspect something weird with the mixing valve or thermostat on the heater.

Sorry for the runaround. You should try a plumbing forum called Terry Love where you can get an expert opinion.

[Linea_Norway]

In our previous house we had an expension tank between the private water pump and the water heater. Sometimes the pressure in it would be low and that caused the cold water in the kitchen to pulsate in pressure when the tap was opened. This was easily solved by pumping up the expansion tank with a bicycle pump.

In our current house the main shower is half a house away from the heater. It takes approx 20 seconds for the water to become warm. So often I choose to take a fast shower in the other bathroom, sitting down in the bathroom, being carefull not to spray over the edge.
Once the water stayed very cool, not cold. I told DH and he changed a valve on the heater that he had recently changed. This valve controlled how much cold water was mixed with the warm water.

If you own the house, I recommend you to redo the bathroom and install warm foam plates against the outer walls. And like others mention, insulate the warm water pipe wherever you can.

[Shinplaster]

Do you get hot water in a reasonable amount of time at the sink taps?  If it's just the shower, I wonder if it's a balance spool and mineral deposits issue.  We have a Moen tap from the 90's that would only give cold water unless you moved the controls back and forth quickly between hot and cold to free up the spool. Eventually I had to take the tap apart and replace the spool to get any hot water at all. 

Maybe the first shower dislodges the deposits, so the second shower benefits.

[Allie]

In the master bath, we have a jetted tub that blasts water with significant force, two sinks, and the shower.  Both the tub and the sinks will turn on and warm up...eventually.  If you turn on the tub, the sinks warm up faster, presumably because the tub helps draw the water to the sinks quickly.  The tub is definitely not a water conserving faucet.  That's what makes this so frustrating.  It's like physics is suspended somewhere between the tub and the shower (maybe 15 feet away if you count the rise of the pipe in addition to the 10 ft distance). 

I have been telling my husband his complaints make no sense...because they don't.  It takes forever for the sink taps to get hot on their own, but they eventually do.  But that freaking shower. 

This whole thing is driving my logical brain crazy!