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Old 08-27-2009, 11:57 AM
BigGibraltar BigGibraltar is offline
Join Date: Sep 2008
Posts: 16
Ideal idle hot tub temperature

I have recently purchased a house and it includes a hot tub outside on the back deck. I am trying to figure out the most energy efficient method of using this hot tub.

I plan on using the hot tub about once every 3 or 4 days and prefer a temperature of 104 degrees F.

Which of the following scenarios is most energy efficient?
A: Keep the hot tub at 104 degrees at all times.
B: Keep the hot tub at a low temperature (~80 degrees?) on days when not in use. Set the tempurature to 104 in the morning before work so that it will be ready by the evening.
C: Keep the hot tub at a higher temperature (~95 degrees?) when not in use. Set the temperature to 104 when I get home from work so that it will be ready by the evening.

In other words, what is the ideal temperature to set the hot tub to while it is not in use. Does this ideal temperature vary with the season?

Some additional information:
Location: Seattle area.
Typical temperature distribution can be found here:

If I turn the hot tub off at 104 degrees at 10:00pm, then the following day at 5:00pm the temperature is around 98 degrees. The is with a typical night time temperature in the high 50's and a daytime temperature in the high 60's.
Old 08-27-2009, 12:21 PM
aruvqan aruvqan is offline
Charter Member
Join Date: Feb 2004
Location: Eastern Connecticut
Posts: 16,462
I leave mine at 103 constantly, it gets used about every other day [though right now all I can do is sit on the edge and dabble my feet in because of the abdominal incisions...2 more weeks until i can jump back in]

Really, it only put up my electric bill by about 4 a month at most. Haven't gone through a winter yet, so I cant tell about winter usage yet.
Old 08-27-2009, 12:48 PM
dracoi dracoi is offline
Join Date: Dec 2008
Posts: 8,867
I think you're better off leaving it constant. It would take most of the day to warm up from 80 to 104, so trying to constantly adjust the temperature would make spontaneous use impossible. My spa only heats up about 5-6 degrees per hour. And it only seems to lose about 1 or 2 degrees per hour, so it would only be getting back down to 80 just as I was ready to turn it back on.

I don't know about your spa, but mine uses the pumps to provide heat (most new ones seem to do this). In the summer in particular, it seems like the regular circulation cycles (which turn the pumps on every four hours for a 15-minute cycle) are doing all the heating that is necessary. Even in the winter, it only comes on about twice as often. The basic circulation is necessary regardless of heat.

I keep my spa at 97 during the summer (I don't want to be any hotter than I already am in the summer) and at about 102 during the winter. I don't have any way to specifically measure the energy cost, but it only comes out to about $20-30 a month to keep warm. This winter was so cold, I did put it in a maintenance mode for a month to keep it closer to 80, and did not notice any cost savings compared to the months on either side.

I am also in Seattle (the suburbs just north).
Old 08-27-2009, 10:29 PM
Snnipe 70E Snnipe 70E is offline
Join Date: Oct 2008
Location: San Jose, CA
Posts: 3,787
For the best energy efficiency turn the tub off when not in use.

The problem as stated above when you want to use spa it may not be up to temperature. Also at varinning temperatures it is harder to maintain the chemistry.

My spa uses 38 amps, that is over 8KW. Since adding my spa the useage has gone up. Before my bill would around 900 KWH now it is between 1100 KWH and 1400 KWH.


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