Is it normal for the water in my Sundance OPTIMA spa, to cool from 100 degrees F to 96 degrees F in about one half hour of use?

When I take the cover off, the hot tub temperature is 100 degrees F. In the half hour that I am using the hot tub, there is no cover on it. The outside temperature is 45 degrees F, with a 15 mph wind. I have the 2 pumps going. The 2 speed pump is on low. The 1 speed pump is on.

I am not using the "air bubble" pump nor do I have the valves on the side open that introduce air bubbles into the hot tub. If I use air bubbels, I can feel that the air coming into the tub is cold. For that reason, the above test is without air bubles.

The hot tub is sitting on top of a wooden deck that is about 3 feet off the ground.

The entire time I am in the tub, I can feel "hot" water coming into the tub. The hot water comes into the tub though a low pressure jet next to the light. The water is not scalding hot, I can put my had on it without my hand getting feeling like it is too hot.

Despite hot water continouly flowing into the tub, in about a 1/2 hour the tub temperature drops 4 degrees F. The water cools from a comfortable 100 F to a less then desirable 96 degrees F.

Is it normal for the water in a hot tub to cool of so fast? Or is the heater on it's last legs, and not putting enough hot water back into the tub? I have noticed the water temp cooling off almost everytime I have used it (about 6 times so far) and now I am closely monitoring it.

I just bought, and installed this used hot tub.
Hot tub info:
-brand name, Sundance Optima,
-Year 2000
- Previous owneres of this tub, took good care of it, and did not use it very much.
- It is wired to a 60 amp ciruit, 220 (or 240) Volts, so the heat does run, even when both pumps are running.
- 2 speed 2.5 hp pump
- 1 speed 2.5 hp pump
- It has "dense, full foam insulation"
- A "sentry smart heater', the literature says it is a titanium heater elment.
- It holds about 485 gallons of water.
- hot water is coming into tub the entire time I am in it. It is not very, very hot water that comes into the tub.
- I have a cover on the hot tub when I am not using it. The hot tub is able to maintain it's set temperature when the cover is on.

Additional information.
- When I filled the hot tub, it heated up at a rate of 5 to 6 degrees per hour. Outside temperature was aobut 70 degrees F. Cover was on.

Is it normal for a hot tub to cool off so fast during use?
Is the 5 year old heater not putting out as much hot water as it used to be able to put out when it was new? Again, I am NOT injecting air into the water via the "air-blower" pump or the 5 air "knobs" that are on perimeter of the tub.

I guess I expect a hot tub to stay at the 100 degree F temperature that I set it at while I am using it. 45 degrees is not very cold, it will get colder then this in Chicago this winter. Am I expecting to much from my Sundace Optima spa that it maintain 100 degree F temperature during use?

Any feedback, questions or ideas is appreciated.

Thanks

Shifty

That is about the right rate of loss, especially in the colder months.

U R correct charger..... at least this is why I think so...

I've monitored outside temperature and hot tub time very closely, and luckly I have had windy and not windy days back to back. Also I remembered a swimmiing pool heater formula for sizing swimming-pool-heaters. The 2 variables were surface area of swimming pool and wind speed.

The day after the first post above, it was the same temperature outside of 45 F. BUT there was no wind. After 40 minutes at 102, temp is still 102 and holding. Wind made the difference.


Yesterday, it was snowing with a 25mph wind, and the air temp is 24 degrees. In 40 minutes temperature drops from 103 degrees to 100 degrees, and that is no air bubbles in tub. Air bubbles quickly cool of the water so I did not use them.

Today same temp, 22 degrees, no wind, and tub maintained temp of 103 degrees for 40 minutes. Man did that feel good sitting in the spa today. My wife turned on the air bubbles at the end of the 40 minutes, because she was getting hot.

Therefor I conclude the heater is ok for a NOT windy day. If it is windy outside, then the heater is not good enough to keep water hot.

So... what can I do to stay HOT on a 15 F degree day , in a blizzard, with the bubbles on?
1 Buy floating insulating Balls?
2 Or build a little wind-break fence?



Problem solved?

Shifty,

Water surface area is the biggest loss of heat (around 80%), and agitating the water and/or adding air flow across it is a major contributer of heat loss. Hence the reason people use solar covers on their pools. Their pool would heat faster with out them, but the wind will take the heat away faster then it can heat without them, so the compromise is to use a solar blanket. In spas, people do very well with a wind break. Even a simple lattice work baracade between the common wind direction and the tub can make quite the difference.

The floating spheres would help greatly, but I wouldn't recommend them, as it would destract from the experiance, and in some tubs could actually be sucked into the fliter systems.

Yup, I agree with you Charger,

I am going to Home Depot tomorrow AM, and will start building a 5 1/2 foot windbreak on 2 sides of the hot tub.

I'll update this with results upon completion.

Shifty

Allright, after a solid 2 weekends of work
I have a fence on 2 siides of hot tub.

Yup it sure is alot less windy when I sit it the tub.
How windy it is makes a difference to my tub's temperature. Less wind makes it easier to maintain temperature

I will add a few boards on other side of deck to try to cut wind a bit more.

Hot tub temperature does seem to maintain a bit better now.
Outside temp is 22 degrees F.
Starting water temp has been dialed down from 104F to 103F. A little bit cooler.

Conclusion = fence helps alot.

Shifty

Crazy huh.... lol

As an update, after 1 + years of hot tub use, I can conclude the following.

1. Wind speed is the most important factor to make the hot tub water loose heat. If it is cold out and windy, the water temperature will slowly drop from 103F, my usual starting temperature in cold weather, to 101 F in about 1 hour.
My Optima Sundance hot tub is unable to pump out sufficient heat to prevent the heat loss on a cold and very WINDY day. But it is enough for a 1 hour soak, starting at temp 103, and being about 101 when i get out.

2. My wife's excercise mat, which is a closed cell foam mat, about 2 feet by 5 feet long when open, or about 2 feet by 2 and a 1/2 foot when closed, helps reduce the rate of heat loss, since it decreases the effective surface area of the hot tub water. Insead of it being about 36 square feet of surface area ( about 6 feet x 6 feet), the hot tub has an effective area of 26 square feet ( less 2 feet x 5 feet)
Her excercise mat also doubles well as a place for me to put my beer.

3. Hot tubs are the most fun in the winter.

Cheers
A Shifty 1.