110 Volt Hot Water Heater Element

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Old 05-12-14, 08:32 PM
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110 Volt Hot Water Heater Element

I need to heat a 6 foot long, 2 foot wide, and 2 foot tall poly stock tank. We're going to use it as an improvised hot tub to soak in. Keeping the cost low is important.

Wood fired heater is NOT an option. It would be easier tho. I have ordered a 2000 watt 110 volt water water heater element and matching thermostat.

I am aware of the potential shock hazard. The element will be completely disconnect before the tank is occupied. Obviously, there is a way to do this safely. After all, the same element is immersed in water for its original/intended use in hot water heater.

My question: Will 2000 Watts keep this volume of water comfortably warm? I plan to insulate with professional-level 3 inches of spray foam, and cover with 4 inches if rigid foam which will be covered with UV resistant vinyl as used for hot tubs.

Please, no suggestions about buying a new/used hot tub. Also, no negative or insulting posts about potential risks. I need the experts help on this.
 

Last edited by upsidedowngreen; 05-12-14 at 09:26 PM.
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Old 05-12-14, 09:15 PM
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If filled to the brim that tank will hold roughly 180 gallons of water. That is roughly 1400 pounds of water. It takes one BTU to raise the temperature of a pound of water one degree Fahrenheit. Assuming you start with 50 degree water and you want 104 degree water, the recommended temperature for a hot tub, you will need to add roughly 77,000 BTUs of heat. Even if we assume the tank starting from half full, to allow for the water displaced by the people, you have 700 pounds of water which would require almost 38,000 BTUs of heat to raise the temperature from 50 to 104. Since electric heat is about 3400 BTUs per kilowatt your 2,000 watt element will add about 6,800 BTUs per hour and at that rate, assuming no losses (there will be losses) it would take roughly 5 and a half hours to heat the water. I suspect the losses could be as high as fifty percent so that would mean 10 to 11 hours to heat and as the water is heated the losses become greater. So, no, I don't think that heater is going to cut it.

Here is another way to look at it. A standard electric water heater has 4,500 watt elements and it will take about 1-1/2 hours or more to heat 60 gallons from about 50 degrees to about 120 degrees. Or, look at a whirlpool bathtub with a 1,200 watt heater. The heater in a whirlpool tub simply cannot raise the temperature of the water, it only serves to slow the rate at which the water cools.

Bottom line, I would suggest at least four times the heating supply.
 
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Old 05-13-14, 02:42 AM
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Ok you need a recirculating pump. A small hp/rpm will do but being hot tub I'd go at least 1/2 hp 1725 rpm piping can be done in 1/2 grey PVC . You can sit tank and pump where ever. Sit tank and pump close to a solid power source. You then route and run sched 80 grey PVC from tank to tub. Length of run will not matter. You will fill tub by hose etc.. Install a light or toggle switch on tank or male plug ended extension cord. If switch is used run power from supply thru switch to tank wiring flip switch. If extension cord plug in. Unit will have to initially run for a long period unless hot water used to fill tub. Keep pump pumping tank powered up and allow tank thermostat to cycle tank. You can come and go at will. WATER LEVEL MUST BE MAINTAINED unless you purchased a marine tank. I'm sure you did not purchase marine tank. Keep water level steady a small amount of chlorine you got yourself 1 heck of a hot tub. You insulate tank will just sit pump will recirculate. You could wire multiswitch system and have pump cycle off at certain temp also have override switch that if your in tub pump is constant. You come off tank thermostat to pump when stat is satisfied tank stops so does pump. Tstat calls for heat tank energizes energizes pump. You would need another switch with constant power and while in tub tank thermostat switch is in diffinent off position constant power switch on. Same for tank switch if it's at on position constant power switch needs be at diffinent off position. If not you will know as soon as stat calls. You will get direct ground. Pump also needs be 120 vac and like I say 1/2 hp 1725-1750 rpm you'll be talk off your neck of woods. ***link removed***is good start for pump or your local pump dealer. My personal fav is bell & gossett they seem to deal with temps the best but are expensive big time. Basic set up is all you need. There will be up front cost for pump switches and piping but once online will operate at minimal cost. You will need to find recirculate piping system. There is supply and return lines. It's easy sneezy if stop look listen and heck even smell. Draw out your piping also your wiring diagram. Electricity too travels in a circle if circle or pipings broke it will not work. Recirculate system only way it will work otherwise tank water will just sit and remain inside tank. Once that small amount of water hot tank will cycle off tub water just sitting at ambient temp. Good luck and good tubbing.
 

Last edited by lawrosa; 05-13-14 at 03:12 PM.
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Old 05-13-14, 06:25 AM
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Furd makes accurate points. It can work but will take a while and a 2kw heater is possibly not the best solution.

My spa is 300 gallons and has a 2kw 120 volt heating element similar to what you are suggesting. The body of the spa is filled with rigid, sprayed in place foam and is covered with a 3" thick insulating cover. With a fresh fill it can take a solid day for the water to come up to temperature depending on how cold the fill water was. Once up to temperature the element has no trouble maintaining it's temperature. So, 2kw can do the job if given enough time.

Since you have a 2kw heating element on order that is more than can be powered from a standard 15amp 120 volt circuit and is the limit for a 20amp circuit. You will probably need to install a special electrical circuit for your tub. I would go with something more powerful like a 4'500 watt 240VAC element and only turn on the power when you know you are going to use the spa. Maybe turn it on when you get home from work so it's ready for later that evening. You could plop a small submersible pond/fountain pump in the water to stir the water for more even and efficient heating. This way you're not paying to keep a massive pot of soup hot for just occasional use. Just make absolutely certain that all electrical devices are disconnected from their power source and removed from the water before touching the water.
 
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Old 05-13-14, 09:07 AM
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Thanks for all the info. We'll probably be able to use the same water a few times as I'll be adding peroxide based product. I understand it won't heat quickly, but it will maintain. I'll definitely unplug everything before jumping in.

220 volt is not available at the tub's location. The 110 volt breaker I'm connecting to is 20 AMP GFI.
 
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Old 05-13-14, 09:23 AM
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Based on NEC code the largest continuous load you can run from that breaker is 80% or 1920 watts.
 
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Old 05-13-14, 10:04 AM
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220 volt is not available at the tub's location
Neither is 110. Nominal voltage is 120v.
 
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Old 05-24-14, 08:21 PM
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120 volt element brought the water up to 104 degrees in 7.5 hours. wondering about the thermostat though. the thermostat I purchased is the lower half for an electric hot water heater. it is 240 volts. what will happen if I use it for 120? I am unable to find one for 120 volts.

no worries I promise I'll unplug the whole thing before we ever use it.
 

Last edited by upsidedowngreen; 05-24-14 at 09:12 PM.
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Old 05-24-14, 09:43 PM
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It is just a switch. A switch can be used for any voltage up to its maximum rated voltage.
 
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Old 05-25-14, 06:15 AM
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Have you worked out a plan for how your thermostat sense the water's temperature? In a water heater the sensing pad is held firmly against the steel side of the tank. The thick plastic side of your stock tank will insulate it a good bit from the water. I'm wondering if covering the whole thing (thermostat and bit of tank around the thermostat) with insulation will help it better sense the water's temperature.
 
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Old 05-25-14, 02:52 PM
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Thank You. I'll Install Now.

Rob Bailey
 
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Old 05-25-14, 08:36 PM
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I have thought about this in my thoughts my plans are to do the same as what you suggested. I will monitor the temperature of the water with a thermometer and adjust the thermostat accordingly.
 
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