How can I determine the volume of our hot tub?

[Solvangswimmers]

We have a 12-year-old hot tub whose manufacturer was "bought out" years ago and we have been unable to get a copy of any owner's manual for this particular make and model. How can I determine the volume of water it holds (eg. in gallons) so I can more accurately do the pool chemistry balancing? Help please...

 

[PaulR]

I had a similar situation, the previous owner left all kinds of owners manuals except for the spa and pool; I don't even know for sure what brand the spa is, never mind the model.

In most cases a spa has a reasonably regular shape if you conveniently ignore any sculpting of the seats and so forth. Mine is your typical square with a footwell, which you can model as two boxes (one being the footwell and one being everything else). Figure the volume in cubic feet and multiply by 7.48 to get gallons. Round to the nearest 50, that's close enough. Then if you find you're always overshooting or undershooting the chems, tweak the estimate up or down accordingly.

The topic came up previously with respect to a free-form pool, see:
http://www.troublefreepool.com/estimating-a-free-form-pool-volume-t11772.html
The talk about measuring volume chemically would be really fussy to get right in something as small as a typical spa. I'd just pull out the tape measure and call it close enough.
--paulr

 

[cobra46]

Next time you refill it, read the water meter before and after. Make sure you aren't running any other water in the house however.

 

[Solvangswimmers]

To Cobra46 -- good idea -- thanks -- why didn't we think of that! L & L

 

[PaulR]

If it's easy to read the water meter, obviously that's best. I have never lived in a house where it was easy, though, so it never occurs to me.
--paulr