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Old 03-29-2016, 07:35 PM   #1
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Not enough hot water to fill tub. Just get a bigger tank?


My wife loves to take baths and the fact that our recently purchased home has a large whirlpool tub was a big plus for her. The problem, is that there seems to be only enough "hot" water to fill the tub 40-50% before it goes "lukewarm". My wife likes the water HOT. And no, neither the dishwasher or the washing machine are running.

So the first thing I tried was turning up the hot water heater to level 2 (of 3) hoping that the hotter water would "go farther", but it is still not enough. The water heater is a typical 40 gallon gas unit (<5 y/o) in the basement and the master bath is on the 2nd floor.

I started looking into tankless heaters and their magical "endless" hot water, and quickly learned that there are a lot of downsides such as more expensive, possibly more prone to repairs, there are only 2 of us so the savings may be negligible (may even use more energy), there is a longer delay before the water is hot at the tap, etc.

So is the solution just to get a larger tank? Add another tank in parallel? Get a big condensing unit?

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Old 03-29-2016, 08:10 PM   #2
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Re: Not enough hot water to fill tub. Just get a bigger tank?


40 Gal is kinda small for anything over 3 people and a 'normal' bathtub.

You already know the downsides of tankless. They are not the cure all that some think.

One of the big factors on tank water heaters is recovery time.

You did not state if you are using gas or electric. If gas, then just go bigger and pay attention to the recovery time. More is better.

If you have electric, then tankless 'might' start to make more sense. As an option, a hybrid electric with a large enough tank would save you money in the long term. A hybrid electric heater is basically an electric water heater that uses a heat pump instead of resistive elements.

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Old 03-29-2016, 08:16 PM   #3
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Re: Not enough hot water to fill tub. Just get a bigger tank?


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40 Gal is kinda small for anything over 3 people and a 'normal' bathtub.

You already know the downsides of tankless. They are not the cure all that some think.

One of the big factors on tank water heaters is recovery time.

You did not state if you are using gas or electric. If gas, then just go bigger and pay attention to the recovery time. More is better.
I did mention that it is a gas unit, so the question becomes, just add another tank in parallel, since the existing one isnt that old, or just get a big one. if just a new bigger one, is it worth it to go condensing? Can I sell the old one for a couple hundred bucks?
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Old 03-29-2016, 09:11 PM   #4
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Re: Not enough hot water to fill tub. Just get a bigger tank?


Ya know, I re-read your post when I was writing mine and didn't see the 'gas' reference.

Sorry about that....my bad.

Adding a second one? How far is the upstairs bath from the water heater? If you have room for a gas water heater, that might be a great option to both speed up the time you get hot water and add more capacity.

If no space, I'd just go with a bigger unit. Condensing? Depends on what the cost difference is between it and one with a longer warranty (and better insulation).

Once again, you have to look at the recovery time.

I have a 50gal unit in my house and I've never ran it out of hot water.
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Old 03-29-2016, 09:16 PM   #5
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Re: Not enough hot water to fill tub. Just get a bigger tank?


Whats a good recovery rating to look for? I'll have to see if i can find the specs on my model for reference.
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Old 03-30-2016, 04:13 AM   #6
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Re: Not enough hot water to fill tub. Just get a bigger tank?


Mine is expressed at Gallons per hour. I believe it's 83. I'm out of town right now on business so I can't look.
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Old 03-30-2016, 06:24 PM   #7
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Re: Not enough hot water to fill tub. Just get a bigger tank?


Make sure your hot water is not higher then 140 F. Over 140 F the plastic piping starts deforming and if your cast iron the tar coating is washed away. Not to mention the scalding issue.

Get your self a larger tank our a high recovery tank.
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Old 03-31-2016, 08:36 AM   #8
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Re: Not enough hot water to fill tub. Just get a bigger tank?


Filling the large whirlpool tub in a matter of minutes will probably exceed the recovery time of any tank water heater. We're talking gallons per minute, not gallons per hour.

A tank heater may be advertised as able to give X gallons in the first hour, X being somewhat larger than the tank size. That does not mean X gallons in ten minutes.

If you crank up the water heater dial to "very hot" you will, by adding more cold water to the mix, fill the tub to a higher level before the water goes cold. But there are several disadvantages as already mentioned plus you will shorten the life of the water heater.

Since you want to draw that much hot water all at once you have two choices:

1. Preheat more of it (get another or larger tank heater).

2. Heat water on the spot and quickly (get a tankless heater).

A water heater will get water to the desired temperature faster if you add a preheater. A passive preheater might consist of several yards of finned pipe such as dissected from baseboard hot water radiators. This would be mounted zig zag on the basement wall or ceiling, out of reach of persons' heads and shoulders. Still not fast enough for a tank type heater.

I am guessing that for tank heaters, the fastest recovering consumer grade electric heater is slower than the slowest consumer grade gas heater.
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Old 03-31-2016, 08:41 AM   #9
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Re: Not enough hot water to fill tub. Just get a bigger tank?


Talked to a plumber that I got a good reference for and he confirmed essentially what most of you have said. If there is the room for it, which I believe that there is, add a 2nd 50g tank. My only concern is that is essentially doubling the cost of heating water in the house. the other option is to replace the 40g with a big ol 75g+ tank but they are considerably more expensive.
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Old 03-31-2016, 09:13 AM   #10
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Re: Not enough hot water to fill tub. Just get a bigger tank?


While reading this, I had questions.

1. Why doesn't the tub have it's own built-in heater?

Or do I not understand how they work?

2. Maybe a tank less unit for this tub only?
That way you are only heating what you use, and won't need to have a larger more expensive tank installed.


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Old 03-31-2016, 09:54 AM   #11
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Re: Not enough hot water to fill tub. Just get a bigger tank?


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1. Why doesn't the tub have it's own built-in heater?
It just has jets. Hot water is provided by the water heater. It sucks the water out of the tub and then blows it out of the jets.
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Old 04-01-2016, 07:58 AM   #12
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Re: Not enough hot water to fill tub. Just get a bigger tank?


How often is the whirlpool used? Twice a week is enough to justify keeping two water heaters in action.

With less frequent use of the whirlpool you could shut off one of two water tanks some of the time.

For water tanks of different sizes connected in parallel you will need to open the water valve for the smaller tank only partway so you get most of the hot water out of the larger tank before the smaller tank starts to infuse cooler water into the mix.
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Old 04-01-2016, 08:09 AM   #13
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Re: Not enough hot water to fill tub. Just get a bigger tank?


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For water tanks of different sizes connected in parallel you will need to open the water valve for the smaller tank only partway so you get most of the hot water out of the larger tank before the smaller tank starts to infuse cooler water into the mix.
Ah, good point. I'll ask the plumber about that if we decide to move forward.
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Old 04-01-2016, 08:29 AM   #14
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Re: Not enough hot water to fill tub. Just get a bigger tank?


The effectiveness of the tank and its ability to recover from the temperature change can be affected by the scaling of the elements inside the tank. It might only need a replacement element to remove this issue.
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Old 04-01-2016, 08:40 AM   #15
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Re: Not enough hot water to fill tub. Just get a bigger tank?


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The effectiveness of the tank and its ability to recover from the temperature change can be affected by the scaling of the elements inside the tank. It might only need a replacement element to remove this issue.
I thought about that but the tank is less than 5 years old, manufactured 12/2011.

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