75 gal. or 50 gal. hot water heater

BongoApril 10, 2014

We recently bought a house and are replacing the hot water heater before we move in. The old heater was 40 gallons, but we are trying to decide what size tank do we need. We are a family of 2 adults, 1 toddler and 1 on the way (so soon to be a family of 4, 3 of whom are females). We have 2 full bathrooms with regular bathtubs, nothing fancy; and 1 powder room. We also have a dishwasher and 1 old-fashioned washing machine that uses a lot of water. I believe all of the faucets/shower heads we bought for the house are 2.5 GPM. Both of us like to take long showers, maybe 25-30 minutes, plus there is a daily bath for the toddler, etc. We also expect visiting family sometime in the future - so the need for 4 showers within 1-2 hours - would be a necessity. I would prefer not to stand by the bathroom door with a timer and/or limiting everyone's showers to 5 minutes. We are making a lot of other energy-efficient improvements to the house, but this is one area where I think we should go with 75 gallon tank.

Any thoughts? Opinions? Your personal experiences? Did you install a 50 gallons tank that you later regretted? Did you install a 75 gallons tank and later wished you went smaller?

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Of these two choices, I recommend getting a 50 gallon hot water heater with a 50K BTU input. This will produce 88 gallons of hot water during the first hour. You want a hot water heater that has a fast recovery. The 75 gallon hot water heater only has a 55K BTU input. It more storage but it takes longer to reheat the water.

You will be amazed how little hot water you will be using with your new faucets and shower heads. Washing machines don't use that much hot water since most clothes are washed in either warm or cold water. A dishwasher also uses little hot water. I personally set the dishwasher on the 4 hour timer so it using hot water during the middle of the night.

    Bookmark   April 10, 2014 at 8:17AM
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I recently installed a Bradford White M-2-TW-50T6FBN - 48 Gallon, 67,000 BTU (natural gas) input for my family of 3 plus a baby.

48 Gallons is more than enough to fill a standard tub, and math says that it is enough to supply 19 minutes of pure hot water without resupply, and with a first hour delivery of 108 gallons, we could run one shower all-hot for 43 minutes.

In practice, hot water heater seems to barely run after showers are complete (reflecting reality, that much less than 2.5 gallons / minute of hot water are used, and most hot water used during the shower is being replaced during the shower.)

I am more than happy with the 48 gallon tank, but think that 67k input is likely a bit overkill for our needs (we rarely take sequential showers.)

Good luck!

    Bookmark   April 10, 2014 at 12:06PM
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I think you need a 75 gallon model or, if your water supply isn't too hard, a tankless heater.

With a 2.5 gpm shower head mixed at 2/3rds hot and 1/3 cold, a 50 gallon tank gives you 30 minutes of showering. At that point, you have 50 gallons of (at best) lukewarm water in the tank. You'd probably need to wait 30 minutes from that point until the water in the tank is again hot. If two are showering at once and no other hot water is being used, it'll start getting cool after about 10 minutes.

If you're using a lot of hot water, there isn't going to be that much difference in operating expenses between the two sizes, you're going to be burning BTUs to heat water either way. You can easily cover the cost difference with the savings you'd have by replacing your old washer with a front loader.

    Bookmark   April 10, 2014 at 1:27PM
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The 50 gallons we are thinking about has (1) 55 gal. recovery (2) 50,000 btu and (3) 88 gal. first hour rating. The 75-gal. model has (1) 60 gal. (2) 55,000 btu and (3) 131 gallons. Does that change anything? I agree with Mike_home that we need something with fast recovery...

    Bookmark   April 10, 2014 at 2:07PM
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No it doesn't change anything. The 50 gallon unit will keep you in hot water. :)

    Bookmark   April 10, 2014 at 2:58PM
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If current hot water heater isn't failing, I would suggest waiting to replace until you've lived with the (presumably) standard input 40 gallon tank and have an idea of how well it works or doesn't work for your needs.

Your experience may well inform your decision on what you need when you replace.

    Bookmark   April 11, 2014 at 7:28AM
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We have a 60 imperial gallon 'OSO' brand stainless steel DHW heater. It heats the water to 175F and has a mixing valve that brings the temperature down to 120F at the output when there's a demand for hot water. The advantages are that being stainless steel, it's liking going to last as long as the building is still standing, far less prone to developing Legionella that's inhaled during showering as the water is atomized and the 60gal tank at 175F is the equivalent to a standard 90 imperial gallon tank in a smaller package ( but physically still pretty large). It also came with a 15 year guarantee.


    Bookmark   April 15, 2014 at 10:24PM
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If I recall correctly (the last time I looked up legionella), 140 degrees F was all that was needed. At that temperature, it tended to be a continuing problem in electric heaters (because of the cool water zone below the lower element) and not a problem at all in gas devices.

What's your thinking for using such a high setting?

    Bookmark   April 16, 2014 at 12:36AM
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