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I'm thinking of doing something
like that, using a plastic storage box instead of the wood
QUESTION:I've seen this done but don't know the details. Has anyone tried it?
Someone took an electric water heater heating element and fixed it to
float in a hot tub. When the water got hot they unplugged it and took it
out.
They made a little wooden platform to float and the element stuck down
through it into the water. They said it was important for the top of the
element not to get wet. They attached wires and a 110 plug.
This worked well for a while, even on a big readymade hot tub. Then it
stopped working and they never fixed it. I'm thinking of doing something
like that, using a plastic storage box instead of the wood, to better
protect the top of the element from getting wet.
They used a heating element ordered from a RV catalog, nearly $100.
Would that really be better than one from a hardware store about $30?
ANSWER: I have several similar devices that I use to heat water baths to keep large
quantities of food hot while catering.
I buy the 120 volt water heater elements (surplus or from the hardware store).
I attach a cord using high quality rubber jacketed SO or SJO type cable. The
ground wire is bolted to the element body via a drilled and tapped hole.
I fit a piece of PVC pipe over the big hex so that it extends above the
terminals an inch or so. I seal the flats of the hex against the PVC with
putty. I then pot the connection by pouring the PVC pipe cavity full of
self-leveling (thin) Dow RTV. I do it in several layers, allowing a slight
skin to form between layers to speed the cure.
An alternative method is to coat the terminals with RTV and then pot the
assembly using epoxy. I like the RTV better because it remains flexible and
won't pull away from the cord.
The whole assembly is then dropped down in the water. It is completely
waterproof and there is no leakage path for the electricity. I run the
heaters on a GFI outlet just in case.
I have a couple of these that are almost 9 years old and still working fine.
If the heater is to be placed in a plastic container, clamp a couple of split
bolt wire splicers on the element, one on each end, to keep the element away
from the plastic. Clamp the split nut gently so it won't crush the element.
A dab of RTV on the threads keeps it from coming loose.
An example of my usage is when I need to keep, say, 20 gallons of baked beans
in one gallon jugs hot. I put them in one of the compartments on a wash sink,
fill the sink with hot water and put in an element or two. Two elements will
gently boil the water, keeping the food piping hot. This technique lets us
take our time preparing a big catering order and still have everything piping
hot when it's time to serve.
If you want to keep the power density lower so the element surface won't get
so hot, use a 4.5kw 240 watt element and run it on 120 volts. This will
output a little over 1kw. Because the element is much larger than the 120
volt version, the power density (watts per sq inch) is lower and thus so is
the temperature.
I should note that a hot tub of any size requires several kw of heat to
maintain temperature. Even running the element on 240, it might not make much
of a dent in a normal-sized hot tub.
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