We moved into our new house last week and used our whirlpool tub for the first time. Guess what, we ran out of hot water.
We told the builder about the problem and he had a plumber install a 40 gallon electric hot water heater in series with my 48 gallon gas water heater (builder pick up the cost). I now get 120 degree hot water into my AKER (ACC2-6060) 100 gallon whirlpool tube (average operational volume 74 gallon).
My question is:
Is this a good solution?
Will the electric hot water heater cost a lot to operate? I have a by-pass valves to both units. There are only two people living in the house that require hot water.
Your putting hot water into a tank that hot water is being depleted. I have a question, why do you not have a heater especially for the tub? A heater that would reheat the tub would be a better solution in my opinion. Like what they use for spas? Probably no one planned for one, oops.... Drawing off hot water from water heater constantly will be a loosing proposition especially when it is cold. Since you have gas why did they put in an electric? Probably easier, not. I would have gone for a bigger gas heater, like an 80. Gas usually recovers faster than electric. Did you try pushing up the temp on the gas heater first? It would be worth a try. You should be able to get 140 ish out of the water heater. 120 is bit hot for tub, 105-107 is a better temp. I tried my tub at 110 for awhile and passed out once. Fortunately the wife was watching me carefully and woke me up before I drowned. . A electrical shut off for the electric heater, like a timer will allow you to heat when you need it and not other wise. Guessing for your area of the world, gas is cheaper to heat with than electricity. It is here.
can you insulate the tub? can you insulate the hot water pipes? either or both will help
The power consumption will be used as according to the usage. In anycase you have to generate a certain amount of BTU's of energy to heat a specific body of mass. If you use less hot water, the cost will be lower. If the water is not leaving the tank, since it is thermostatically controlled, the heater will only use energy when the water temperature drops below it the set value by the thermostat. If the water is not moving out of the tank, the maintenance heating will be very little. The water has a lot of mass and will stay hot for a long time.
it will work Ok the quick answer was probably that you didn't have enough flue size to do a second gas heater. depending on the cost of natural gas the electric may not be too bad there should be energy stickers on both to give you an idea of efficiency. You may want to wrap the heaters but that is another thread entirely!
You defiantly needed 2 heaters. instant ones also require lots of intake air as well as flue due to high BTUs. make sure the second tank and first are set for about the same temp. If the electric is second and electricity cost a bunch more you could kick the gas temp a little higher making the electric a little less likely to heat. If the electric is cheaper due to gas cost (here in Colorado it just jumped
70%) then you could lower the gas temp a little bit and let the electric heat the water a bit!
you can get a timer for the electric to turn the heater on and off so if you knew you were going to use it at a certain time of day you could bypass it and have it turn down. I guess the next step would be to get a solenoid installed on the valve so you could open and close it from upstairs!
SQLit has some good points. The tub should have its own heater. The larger question is how often do you use the tub? So will you be operating the hot water heater a lot?
I don't understand your bypass valves? why do you need bypass valve? You should only need additional valves if the tanks are hooked in parallel. If you plan to use only one hot water tank most of the time, then put it downstream in the series condtion. E.g., if gas is cheaper put it downstream and only turn on the electric tank about 6 hours before you plan to fill the tub, then turn the electricity off when you don't plan to use it. If the electricity is cheaper then put it downstream and turn the gas thermostat down as low as possible. If they really are in parallel, which will work ok, all you need is an inlet valve on each tank and then turn the inlet valve off on the tank you don't want to use, water won't pass through that tank.
Which water heater is first? If the cold water goes into the gas unit first, then you're OK. Cause the electric will only come on when you run enough water to purge the cold water through the gas heater. The electric heater will lose some heat, but not like doing all the work heating water.
If the cold water goes into the electric heater first, adn then the gas heater, you're in for a surprise. Cause the electric will be doing most of the work.
This will work fine (though they are idiots for putting a whirlpool spa on a 48 tank in the first place).
The gas should be first to preheat all the incoming cold water. Then most of the time the electric will just maintain heat. An electric has less standby loss as there is no flue up the middle and no uninsulated area to speak of unlike a gas heater.
Bypasses are fine in my book, belt-and-suspenders backup, it means you can maintain service during repairs if one tank goes out. (However, Gary has pointed out that he doesn't like bypasses because he feels crud collects in them.)
I *DISAGREE* that the tub should have its own tank. Lets see now, it takes more than just a 48 gall to run the tub. So now you have a 48 plus a 40 (88 total). If you had separate, you'd still need at least a 40 for the rest of the house, plus BIGGER than a 48 for the tub. More total capacity installed, more total cost. And you'd have the big tank sitting there most of the time unused, not contributing to the rest of the house. Right now, when you are not using the tub, you have ample capacity to run simultaneous clothes washing, dishwashing, showers, guest showers etc. You would not have this with separate tanks unless BOTH sides were huge (even more cost). You should NOT put this on a separate tank, it SHOULD be shared.
This is also the type of setup I have, except that mine are 40 and 65 and both indirect fired (oil fuel) off the main boiler.
It's a good one if the cold one goes into the heater that's cheapest to operate _first_. Which is usually gas (which is the assumption below).
It'd be _better_ if they used a larger single unit or a second gas one, but that may have been impractical if your flue wasn't rated for it.
Under normal conditions the electric heater will be pretty cheap to operate because it's only maintaining an existing temperature, rather than having to heat cold water up.
As an additional comment - you could have increased the temp setting of the water heater, and get more hot water at the desired temperature by mixing with cold.
It is certainly true that running the HWT hotter increases scalding risk. So much so that some jurisdictions (ie: California) mandate a maximum hot water temperature of 120F.
However, many jurisdictions recommend that water heaters operate at 140F (the Canadian govt. does, as does the US CDC) to reduce risk of having the HWT becoming a breeding ground for bacteria (especially Legionaires disease).
You can compromise by adding a mixing valve on the output of the HWT that regulates the water tank's output temperature to, say, 120F by adding cold water right there. Rather like a shower temperature balancing valve. Once you've done that, you could raise the HWT higher (to 150F or even 160F) and still stay within the 120F-at-faucet guidelines, and get enough hot water to fill your whirlpool from just one tank.
Isn't the *best* solution to install 1 huge 80, or 90 gallon gas heater?
2nd best would be, in my book, to connect the electric heater in tandem to the gas, in such a way as it serves as a storage facility only, and does not actually heat the water. Either a small recirculating pump, or natural convection and some clever valving, and you can effectively get the gas heater to do all the cooking, and dump into the electric "tank". The coolest water on the bottom of the electric could be piped directly to the gas heater via T's in the drain valve assemblys.
Normally yes. But this may not be an option for the OP due to space or flue considerations, or not without a lot of additional expense.
Besides, if set properly, the dual arrangement may actually be cheaper to run than one huge tank.
I can never remember whether tandem means "in series" or "in parallel".
Ah, checked an online dictionary. Tandem means "in series". As the OP's contractor _did_ do.
If the gas heater is fed first, and then feeds _thru_ the electric heater, then the gas heater does most of the work, and the electric heater only maintains temp.
Best would have the electric heater T-stat set slightly _lower_ than the gas heater. The electric heater would never go into "demand" mode until the gas heater completely emptied of hot.
By doing a clever criss-cross arrangement of in/out feeds on the tanks, small recirc pump plus a check valve (so the cold feed _cannot_ go into the electric heater), you've effectively doubled the size of the gas heater's tank. You'd not even need heating elements on the "other" tank. Just a tank and insulation.
_However_, this means that you're doubling the "maintainance loading" on the gas WH. These days equipment like this is manufactured with pretty tight specifications, and you may be outside of the design loading on the gas heating components. Ie: possible premature failure.
I'd be concerned it'd void warrantees on the gas WH.
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