Getting 24 gallons of hot water from 40 gallon gas water heater...

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bnymbill

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My tenants complained of only being able to take 7 minute showers, so I measured the output at the tub. I'm only getting 24 gallons of hot water from a 40 gallon natural gas water heater, then it's mixed with cold water and eventually all cold in another 20 gallons.

It's 10 years old, model no. BFG1F4040S3NOV

I flushed the tank and it didn't help. I am thinking it's the dip tube but I would expect cold water to mix in before I hit 24 gallons of hot water if that were the case. The burner has a nice blue flame and the water gets very hot (don't have a temp reading, just to the touch). Any thoughts?

It's going to take quite some effort to replace the dip tube because the basement height is only 5', which means I'll have to drain, disconnect, and tilt the water heater.
 

Terry

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Very old?
It may be filling up with sediment. Sometimes even after draining it's hard to wheel them out because of the lime at the bottom of the tank. I pulled an old tank out yesterday that was pretty messy during draining. I wheeded it out with quite a bit of water still in it to the driveway and pulled the drain, sticking the end of my pliers in the hole to get the sludge to drain out before throwing it into my van.
 

bnymbill

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I got 10 years out of it - maybe it's time to bite the bullet and replace it. I'm in Baltimore and the water mains in my neighborhood were replaced last year, so I could see extra sediment accumulating.
 

CountryBumkin

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"I'm only getting 24 gallons of hot water from a 40 gallon natural gas water heater"

Could you just have a bad element (assuming it has dual elements). I don't know - I'm not a Plumber. Just wondering.
 
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Gary Swart

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Although some water heater live longer than 10 years, that's really old age for a heater. Suggest you replace it.
 

Terry

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Changing the shower head to a 2.0 gallon or less would give them 12 minute showers.
You can either dump all the water out of the heater quickly, or dole it out a bit at a time.
 

hj

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24 gallons is about right for a 40 gallon heater. The temperature starts dropping as soon as the replacement cold water starts to enter the tank, and the colder the water the faster it happens. It also depends on what the initial temperature is as far as how long the hot water will last.
 

HandsomeMike

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24 gallons is about right for a 40 gallon heater. The temperature starts dropping as soon as the replacement cold water starts to enter the tank, and the colder the water the faster it happens. It also depends on what the initial temperature is as far as how long the hot water will last.

I agree. I had a previous instructor that I respected very much who told me that 28 gallons is all that a 40 gallon tank is capable of before the incoming water lowers the temperature enough that it can't recover quickly enough.
 

bnymbill

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This is a gas water heater, so no elements are involved.

I have the Moen Adler valve and trim kit with a 2 GPM shower head. Is it possible the cartridge needs to be replaced? I could also drop to a 1.5 GPM.

I am looking to add a pressure reducing valve to the system as well. One theory I have is that, since the city replaced the water mains and meters, the pressure to the house has increased. The cold water could be entering the water heater (and other fixtures) at too high of a pressure and mixing more vigorously than it should, stressing the valves.
 
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Reach4

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I am looking to add a pressure reducing valve to the system as well. One theory I have is that, since the city replaced the water mains and meters, the pressure to the house has increased.
Pressure gauges can be inexpensive. One with a garden hose thread is convenient.
 

JRC3

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So what temp is the dial set at? But that doesn't mean the dial is accurate. A cheap cooking temp gauge will tell all.

I doubt the possible pressure increase would cause a problem with the tank...The water is only going to enter the tank at the same rate as it comes from the tub spout or shower head.

Oh, is the in and out correct on the heater? LOL Seriously though.
 

bnymbill

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So what temp is the dial set at? But that doesn't mean the dial is accurate. A cheap cooking temp gauge will tell all.

I doubt the possible pressure increase would cause a problem with the tank...The water is only going to enter the tank at the same rate as it comes from the tub spout or shower head.

Oh, is the in and out correct on the heater? LOL Seriously though.

The dial is set two notches from the max, no temperatures on the dial. I will get a temp reading tomorrow. The water steams when running only hot water at the faucet and the tenants tell me it's too hot shower when the valve is opened fully to hot.

It doesn't make sense - 24 gallons of steaming water should provide for a 12 minute shower at max hot. When mixed with cold water, they should be getting at least a 15 minute shower.

The in/out are correct - it's been working well for several years.
 

bnymbill

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Perhaps my problem was listening to the tenants...3 girls, who probably take very hot showers. I stopped by the house today and took a 17:30 shower before running out of hot water. I think that's about right for a 40 gallon water heater.
 

Dana

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Three back-to-back 7 minute showers wouldn't cut it at the current storage temp if it's crapping out in under 18 minutes- the tenants may not be crazy. The average showering time in the US is about 8-minutes, so ideally you'd be able to get 24-25 minutes of showering before it's toast. But it shouldn't take a huge jump in storage temp to get a noticeable improvement.

Install a tempering valve or thermostatic mixing valve on the output of the water heater adjusted to 120F or lower (115F is fine for most homes), and crank the temperature adjustment on the tank to the max, utilizing the thermal mass of the stored water to the extent possible. If the tank gets replaced a tempering or thermostatic mixing valve is going to be required anyway it it's not there already.

If you already have one, turn the tank temp up to the max, and turn the tempering/mixing valve down a bit, if they're complaining about the shower being way too hot with the shower mixer pegged.

A thermostatic mixing valve is preferable to a tempering valve, since it can eventually mix to full-hot as the tank temp drops, whereas most tempering valves will insert a temperature difference between the hot supply and the outlet temperature.

A 115F shower is still way hotter than most people can stand- most prefer ~105F give or take a couple. But 115F may be necessary for suitably hot fills on a cast iron tub. A low thermal mass tub fill temp would be about 110F, give or take.

honeywell_am_1_b.jpg
 
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bnymbill

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I'm not suggesting they're crazy...just that, after having lived there two years, they explained it to me as though there were a big drop in performance. Seems to me that 17.5 minutes is decent, despite having to adjust the handle 5 times during the shower, tested my 2 year old water heater and got similar performance but only had to adjust the handle 3 times.

I like the thermostatic mixing valve idea - should definitely be able to buy them a few more minutes by turning up the water heater temp while preventing scalds.
 

Dana

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As long as they pay on time and aren't wrecking the place it's worth taking at least that small measure to keep them happy, eh?
 

Jadnashua

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I'm a big advocate of a thermostatically controlled shower valve...no adjustments required while the water heater cools off. You still should have a tempering valve at the WH for safety. IT makes it nice between seasons, too, as it will automatically compensate for the cold water's temperature changing...in my home, the variation can be nearly 40-degrees difference between summer and winter cold water supply temperatures.

If the water at the shower can be turned up to an unsafe level, the limit stop should probably be adjusted, but that can change, season-to-season.
 
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