38 ga. tank - not getting 2 hot showers?

[ashe]

We have just finished a renovation project that included moving the water heater. The new location is in the crawl space which is 51 inches tall from the gravel to the bottom of the floor joists. With that size limitation, my contractor picked out a 38 gallon tank without consulting us. The water heater that he replaced was 50 gallons and we never ran out of hot water with a family of four. We are now only two people and our shower heads are 1.5 gallons/minute, but the second shower starts out not quite hot and ends cold.

Is that what we should expect from a 38 gallon electric tank?

We are upset to have this problem and we are wondering:
1. could something be wrong with the tank?
2. the maximum temperature on this Rheem tank is 150 deg. If we got a tempering valve, how much additional hot water would we gain?
3. If we insist that the tank be replaced with a 50 gallon tank, would a 46 inch tall unit fit in the 51 inch space?

Thanks for any help and advice!

 

[Jadnashua]

You're lucky to get 75-80% of the tank's capacity that is hot, and in the winter, typically, your incoming water is quite cold, which dilutes the stored water. What temperature are you running the tank?

If you do raise the storage temp you'll get more effective showering temp water. Code requires a tempering valve if the set temp is greater than 120-degrees F for safety. It comes down to some algebra. X+Y=1.5 X*(hot temp) +Y(cold temp)=showering temp if I thought it through properly (may not, it's late!). That should give you how many gallons of both hot and cold you're using, and then divide that into your tank size. Your WH can extend it's hot water, since it will be heating it while you are drawing it down, but electric WH usually have a much longer recovery time than a typical gas or propane fired one.

 

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[MrStop]

Are you limited to electric?

I'm a little concerned that your crawlspace sounds like it has exposed gravel. It hasn't been sealed with plastic to avoid moisture issues?

 

[MARSappliance]

Not enough hot water -



a 38 gallon should be providing enough hot water for a family of four at about ten min a piece. You may have a problem with the heater.

- Bad bottom element is possible – I would put and ohms meter on the bottom element with the power off – if you test screw to screw on the bottom element – it should reed between somewhere between 9-16 ohms if it is good – if not replace element.

- Code – not all states require satey devices if set above 120. However if you set above 130 I would recommend installing a thermostatic mixing valve – they automatically mix hot and cold to 120 degrees – which means that although your tank is set higher and giving you moor hot water, you are using less of it and reducing scolding risk. They run about 150 at lowes – you will probly have to order it and will also need to check valves – install a crossover line near the start of the heater and all points off use will be mixed properly.


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[Smooky]

The bottom element is probably burned out.

 

[montelatici]

Some of those Rheem 38 gallon shorties come with 3,800 Watt elements, that may be marginal for a family of four. If you have the 4,500 watt version it should be fine. I looked at them and went for the 40 gallon Rheem with 5,500 watt elements and it is way overkill for 4 people. A 50 gallon would be a total waste of energy for sure.

 

[Jadnashua]

It all depend on several factors: how long are the showers, how hot is the tank's thermostat, and how cold is the incoming water. 38g tank, you only get to use about 75-80% of the tank's capacity when you are dumping it quickly, so say 32g/4 showers, or 8g/shower with a 2.5gpm head, given that you're not using all hot in that, maybe 5-minutes each. Depending on how much recovery time there is between showers, while some adults might only take a shower that length, teenagers often are in there for MUCH longer unless booted out! ANd, some adults like a long, hot shower as well.

 

[Dana]

If the tank is working fine and you're still coming up short, a gravity-film type drainwater heat recovery unit can dramatically extend the "apparent capacity" of a hot water heater, and save energy at the same time, since it's extracting a good fraction of the heat that's literally going down the drain and returning it to the incoming water stream (ideally both the cold water feed to the shower and the cold feed to the water heater.)

They run several hundred USD, and there isn't always a good financial rationale for it in cheap-electricity country but a pretty good ROI if you're paying north of 15 cents/kwh. It has to be mounted vertically, which means it depends on how your drains are routed as to whether you can install one at all.

With 51" of head room you're probably looking at a 4" x 36" or 4" x 42" version, best case, which would run 35-45% energy returned at 2.5 gpm, perhaps low- 50s for a low-flow shower.