Everything I have read says that 15-minutes at 104F is the maximum
exposure for a person in good health. Someone who is pregnant, has
diabetes or heart problems should not be exposed to even that much.
The problem, apparently, is that when you get the body to that high a
temperature, the body loses its ability to shed heat. You can find a
lot of information on the large spa equipment websites.
Nope, you don't use the temp to regulate microbe growth any more than you would
with a swimming pool. The other problem with temps over 104 is that is about the
temp where tender skin starts to be injured.
I am curious as to what sort of heating system your hot tub uses? I have
connected power over the years for two types that use electricity for
heating. One uses a 20 amp 120 volt circuit and heats the water only when
the jets are not in use. This unit takes a longer time to heat the water
from cold. The other type uses a 40 or 50 amp 220 volt line and heats the
water up much quicker than the previous one that I mentioned. The heater
can work with the jets going. Of course this type also consumes
considerably more power. Or do you have a gas heater?
If you have the 220 volt model, I don't think it would be necessary to run
the heater 24/7 although you may need to run the pump frequently for
filtration purposes. You could try calling the manufacturer or distributor
to ask them how long it takes for the water to get to your ideal
A couple of manufacturers used to make timers just for hot tubs, but I
haven't seen any lately. I think solid state controls are taking over. Try
doing a search for pool or hot tub time clocks. You could also check
www.grainger.com or contact an electrical supply house. Take a look at
www.tork.com and look up models 1100D and 1100FM under Special Purpose
Insulate it better. There is a spray for the underside of the tub
itself. Another cover for the tip is in order. Then keep it at 95, find
out how long it takes to go from 95 to 103 and educate everyone on the
fact they will have to turn it up ahead of time (and back down). The
exact numbers here are hypothetical, but the cooler you keep it the
more energy you will save.
Turn down temp before work and turn it up after work. Find the lowest temp
that still allows a reasonable return to 103. Manual or timer.
Look into timers (will tend to forget manual resulting in frustration for
Look into solar assistance.
Build 2 sided privacy lattice for privacy and to optimize wind barrier.
Reduce fast food consumption and use money to pay for heating.
Thanks to everyone with all the great ideas!
You're right on target for your game plan.
I just moved from a house with an above ground spa (SoCal)
& I sure do miss it! :(
Soaking in the spa looking up at the stairs was very nice.
I thought I'd tire of it but I never did.
I used to turn the heater off when I was done with it for the night.
I would turn up again a few hours before I wanted to use it. I just
had to remember!
I don't remember ALL the details of the installation like heater power
(kW) but it was ~500 gallons (a deep 6 person, ~8x8 spa)
but I do remember if it wasn't cold outside (<60F) the water never
really got cold (just not good & hot)
& if it was hot outside the spa would pretty much stay usable (103)
without turning the heater on.
If it was tempid (~90's) it would take ~2 or 3 hours to bring it up to
If yours is really 300 gallons then each kW of heater capacity will
bring your spa 1.4 degrees F per hour
I think mine was 5.5 kW & I had 500 gallons
so I could get ~ 5 degrees F per hour,
which was fine as long as I planned ahead (too lazy to do the timer)
but if I forgot..............no spa tonight :( ........or a tempid
The closer to ambient temperature you let the spa temp fall, the more
electricity you'll save
If you've got a 3.3 kW heater you'll get about 5degs F per hour as
So I would suggest you kill the heater at night when you got to bed.
The spa will probably "coast" long enough to do the midnight soak.
(night time loses are greater than daytime) & fire it up a few hours
(3 or 4) before you'll want it hot.
If you measure your water temp in the afternoon & you know when you
want it ready & you know your heater kW you can predict how soon you
need to turn it up based on heater kW
In a pinch I used to run both jet systems full speed to add to the heat
(maybe another 20% capacity)
Great information. I'll test out the 5 d per hour hypothesis. It sounds
like our tubs are/were pretty much the same.
I always wonder, though, does reheating the tub daily cost more than just
maintaining the desired temp.
Well, you would think it's obvious, but if the heater is kicking on 18 times
for 10 minutes (total 180 minutes) to maintain a given temperature versus
running for 3 hours straight to come back to temperature, what's the
mathematical difference? What I'm missing here is some information about
how often and how long the heater kicks on throughout a given day to
maintain the desired temp; so for now my numbers are imaginary.
In our case, with the heater/filter running for two, one-hour cycles,
we only lose a degree or two between cycles. Doesn't take long to get
it back. I usually open the cover and turn on the pump, then go back
in the house to change. By the time I get back, it's pretty close to
temp. Even if it isn't, it will be shortly after getting in.
As I said, the only concept you need to consider is the AVERAGE temp
maintained over time. It really IS that simple and obvious. If your
AVERAGE temp over time is lower, your heater will be running less.
What you are "imagining" happening with your heater is not what is
happening in reality.
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