Inadequate Hot water to fill Spa Tub

Discussion in 'Shower & Bathtub Forum & Blog' started by KyNew, Feb 15, 2021.

  1. KyNew

    KyNew New Member

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    Location:
    Kentucky
    We have a big (5,000+ squ ft), 12 year old house with a brand new 50gal water heater (the largest one allowed). We ONLY have electricity, no gas on our property.
    The hot water capacity is generally fine for everything EXCEPT the large spa tub in our master bathroom. When I turn the hot water on in the tub, it turns cold before the tub is even half full.
    We were thinking of adding a separate tankless heater, just dedicated to our master bath. Thoughts?? Thank you!
     
  2. Terry

    Terry Administrator Staff Member

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    Plumber
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    Bothell, Washington
    You you get propane gas where you are?
    That would at least allow you to finish filling the tub.

    Some places allow for a electric 80 gallon heat pump water heater.
     
    Last edited: Feb 15, 2021
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  4. Reach4

    Reach4 Well-Known Member

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    If "spa tub" means jets etc, check with the maker to see if you can retrofit a heater. That has the advantage of assisting your WH during fill, it can keep the water at the desired temperature as time passes.
     
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  5. PlumbNuts

    PlumbNuts SC Licensed Plumbing Contractor

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    Why is a 50 gallon "the largest one allowed"? I haven't heard that before.

    If 50 gallons is the largest "one" allowed, are there any restrictions against having "two"?
     
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  6. KyNew

    KyNew New Member

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    Hi Terry,
    Thank you for responding. We could have a propane heater installed, but that would be a much bigger project than just connecting a second water heater for this side of the house. We have geothermal system here for Heating. There is a state Kentucky regulation that only allows for a maximum of 50 gallon water heater in a residential home.
     
  7. KyNew

    KyNew New Member

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    thank you for responding. Yes, it has jets in it. It’s quite large. But inside my bathroom. I will look into having a retrofit heater. It was installed probably 11 years ago before we owned the home.
     
  8. KyNew

    KyNew New Member

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    Thank you. Yes, apparently there is a regulation in Kentucky which allows for a maximum of a 50 gallon water heater in residential properties. We used to have an 80 gallon tank but when it failed, we were told we could only replace it with a 50 gallon tank. I don’t know of any regulations that do not allow for two water heaters.
     
  9. LLigetfa

    LLigetfa DIYer, not in the trades

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    You could try turning up the heat on the water heater and add a tempering valve on the heater outlet to blend some cold water to keep it from being scalding hot.
     
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  10. KyNew

    KyNew New Member

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    Kentucky
    thank you. We turned up the heat on the water heater as high as we could. I was told by a couple of different plumbers that the distance from the hot water heater to my master bathroom is just too far to meet the capacity of filling up that tub.
     
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Raise the temperature, insulate any lines you can access, add a hot water recirculating system that will save throwing away all of the cooled water in the lines and let you use much more of the tank. Say you have to run for a couple of minutes before it’s hot. That’s maybe 10-gallons with 10-gallons into the tank cooling off what’s left. With a recirculating system, you get hot nearly immediately without the initial loss and diluting the hot in the tank. Code says you need a tempering valve if the tank temperature exceed 120. Some tanks can go up quite a bit higher than that. If that doesn’t cut it, then think about other, more expensive options.
     
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  12. PlumbNuts

    PlumbNuts SC Licensed Plumbing Contractor

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    Fort Mill,SC
    Based upon all replies it seems that the seperate point-of-use heater may be the right answer for you then.
     
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  13. KyNew

    KyNew New Member

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    Thank you. My question is, is it possible to add a separate tankless water heater just for the master bath? Can I disconnect that bathroom from the whole house heater, even though I have geo thermal heat/air conditioning which runs off of water?
     
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Certainly, it is possible to feed that room with its own heater. Without knowing how your lines are run and where you can place it will determine how easy it would be.
    If the tub is not also a shower, adjust the stop in the valve to allow hotter input. An alternate to that would be a thermostatically controlled valve that will maintain your desired set point until there's not enough hot left.
    Depending on your incoming cold water temperature, to quickly fill a large tub, may require more than one tankless system. Look carefully at the temperature rise with the volume you need in gpm. Your results will vary radically depending on that incoming water temperature. What might work fine in the summer might be terrible in the winter. Get a good thermometer, stick it in a glass in the kitchen sink and run water into it until the temperature stabilizes. I've seen mine get to 33-degrees in the winter. You need to know your starting point.
     
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  15. Reach4

    Reach4 Well-Known Member

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    Location:
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    Since your main water heating is more power-efficient, you could supply the tankless through the main water heater. Then the resistance-heating water heater would only make up the shortfall in heat.

    Electric tankless water heaters take a lot of current, so make sure your electric service can handle that.
     
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  16. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    New England
    Electric tankless systems are mostly a joke except for small point of use applications. Keep in mind most gas-fired ones tend to be like 199k btu would equal about 58.4kw and at 240vac, about 243 amps. You won't find one that big, which means it won't produce enough hot water to match a gas-fired one, and that may not provide enough a high flow trying to fill a big tub.
    Heating a tank to something like 180 and tempering it down to a safe temperature may do it for you.
     
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  17. KyNew

    KyNew New Member

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    Thank you. It is becoming very clear to me as to why I, or my local plumbers haven’t been able to figure out this issue. It’s apparently quite complicated by several questions and possible and probable issues. I really need a Master Plumber to come here, it seems.
     
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  18. KyNew

    KyNew New Member

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    Thank you. It is becoming very clear to me as to why I, or my local plumbers haven’t been able to figure out this issue. It’s apparently quite complicated by several questions and possible and probable issues. I really need a Master Plumber to come here, it seems.
     
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  19. Terry

    Terry Administrator Staff Member

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    People have mentioned a tempering valve on the water heater. You need that anyway with the soaking tub. The tempering valve blends hot with cold down to the desired temperature. Normally that would be 120 degrees. With the tempering valve, you could turn the thermostats up all the way to 160 and blend it down to a safe 120.

    [​IMG]
     
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  20. KyNew

    KyNew New Member

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    Thank you. Yes, we already adjusted it up as much as we can, but it’s not enough. The volume run out.
     
  21. Paulypfunk

    Paulypfunk In the Trades

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    Seattle
    Is no one going to challenge the notion of “a 50 gallon water heater is the biggest one allowed in Kentucky”. This sounds like a lie. What if you have 6 bathrooms? Six bathtubs? I’ve never heard of such a thing. I looked through several Kentucky state regulations regarding water heaters and I found nothing limiting the size. The only regulations I found, which is common language in most Plumbing codes, state that “the water heater must be large enough to handle the demand of the home” or something similar. It seems clear that yours is not.
    Was this new installation permitted and inspected by your local water department? It depends on where you live but they are often required. One reason it to insure that the installer knew what they were doing and another reason is to make sure that the plumber is doing work that is ethical and in your best interest as a consumer, which I suspect they are not. If you or anyone here can quote me the Kentucky law that limits the heater to 50 gallons, I’d like to see it.
    Here is my guess. Your plumber had a 50 gallon heater the wanted to sell to you, or they didn’t do the proper calculations before they bought the appliance, and told you that line about the state law to cover their mistake. I don’t live in Kentucky so I can’t be sure, but I think it’s worth doing some due diligence here. Your local government agency that governs plumbing should be able to give you a straight answer without having a financial interest in the outcome.
    I will also agree with the proposed fix. Add a thermostatic mixing valve on top of your existing heater, then crank the heat up to 160’. This will extend the first hour limit of the tank and make a 50 gallon heater behave like an 80 gallon heater. You must add the secondary mixing device to prevent scalding hot water from leaving the tank.
    Also how big is this tub? You can do some rough math calculations to see how much water will fit in it. Can you ID the make and model? Look up the manufacture data and it will tell you. You could also use watch to time how long it takes to fill the tub. Then drain it and time how long it takes to fill up a standard 5 gallon hardware store bucket. From this you can calculate the gallons needed to fill your tub. Your hwh tank ‘first hour rating’ should exceed this. You said you turned up your heater already? Most heaters have multiple thermostats. Did they all get turned up?
    It doesn’t matter how far away the tub is from the water heater. That doesn’t really affect the first hour rating, you just end up wasting more cool water at the start before the hot water completes its journey from the tank. A more efficient system would be insulated and have a constantly moving ‘Ferris wheel’ of hot water circulating around your home, but that is a matter of efficiency and convenience. That doesn’t really affect how much hot water is sitting in the tank.
    To sum up: Challenge the 50 gallon assumption. If I’m right and your plumber tried to cheat you, insist they make it right.
     
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