Hot tub cover left off overnight. Cold night !! ??

[Sister]

Accidentally left hot tub cover off overnight. From 7pm to 9 am . Cold night in the 30;s . Hot tub was fine and still 104. Can this do damage???? Also, how much jump in electric can this cause?? It is someone else's house which is why I am wanting to know if it would be a huge jump in electric bill. I will tell them if so. 

[Cusser]

Same as if you were actually using it from 7 to 9pm.  Don't worry about it.

[RDspaguy]

They might notice. Figure 30 amps at 240v is 7.2 kw running for 14 hours is 100.8 kw hours. How much does your electric provider charge per kw hour? Probably between 10 and 15 cents. So $10-15 on the bill.  Could vary a bit with brand of spa.

[Cusser]

23 hours ago, Cusser said:

Same as if you were actually using it from 7 to 9pm.  Don't worry about it.

Sorry -I misread the time frame. 

[north_of_boston]

Sister, 

You DO want to be careful ... you do not want water to evaporate below the filter / heater intake level -

I had a family member that had a hot tub - on a porch overlooking a New Hampshire lake.  In the dead of winter.

 Some relatives used it,  and reported that the "cover blew away" - (translation,  a little too much booze and the cover DID blow away) ... and the water evaporated down to the low level - it froze - bye bye hot tub . 

But "cold night in the 30s" -- or -2C -- that's not really that cold - no harm but your electric bill?   The electric company and its stockholders thank you!

n-o-b