Cost to Fill a Tub

[Jet Sitter]

Warning – the following may be of absolutely no interest to many of you!

We’re still working through the process of wet testing and becoming more informed about spas on the way to becoming first time tub owners.  I have read about people stretching the time to empty and refill their tubs, presumably to save the cost and hassle.  I have also read how people say there is nothing like the great feel of a freshly filled tub.  So I got to wondering what it costs to fill a tub.

If you don’t know and are curious, here’s the calculation I went through.  Please feel free to let me know if I have made a mistake (my wife is very good about this).  I have provided a couple of equations at the end of this post to simplify matters if you want to calculate your own actual cost.  But first, I’ll describe my process so you math whizzes can correct me if I am wrong.

The cost to fill your tub includes the cost of the water, the cost to heat the water and the cost of start-up chemicals.  In Seattle, we pay for the water at the rate of about $2.70/CCF supply and $7.80/CCF sewer or a total of $10.50 per CCF.  There may be higher rates charged for excessive use, but generally these figures apply.  One CCF = 748 gallons or one gallon = .00134  CCF.  So, one gallon water costs $10.50 x .00134 = $0.01407.  The cost to fill a 400 gallon tub would be about 400 x $0.01407 = $5.63.

But unless you enjoy a cold dip, the water must be heated.  The energy to raise one pound of water one degree Fahrenheit at sea level is one BTU.  One gallon water weighs approximately 8.34 pounds.  So to raise one gallon one degree takes 8.34 BTUS.  One Btu equals 0.00029307107 kilowatt hour.  So to raise one gallon one degree takes 8.34 x 0.00029307107 = 0.002444212 KWH. Assuming my water arrives at 50 degrees, and I want to heat it to 102 degrees, I need to raise each gallon 52 degrees.  If I have a 400 gallon tub I need 52 x 400 x 0.002444212 KWH = 50.84 KWH.  Seattle City Light charges me about $.08 / KWH for electricity.  The cost for me to heat the 400 gallons 52 degrees would be $4.07.

The total cost of my 400 gallons of water heated to 102 degrees would be about $9.70.  I would appreciate any input that you can provide regarding start-up chemicals as I have no idea about this at this point.

If you want to know the cost to fill your tub use the following equation:

Cost to Fill = Tub Capacity (Gal) x Cost for Water ($/CCF) x 0.00134 (convert $/CCF to ($/gal)

Example, for me: 400 gal x 10.50 $/CCF x 0.00134 = $5.63

If you want to know the cost to heat your freshly filled tub use the following equation:

Cost to Heat = Tub Capacity (Gal) x Temperature Increase (Degrees F) x Cost for Elec ($/KWH) x 0.002444 (convert gallons to pounds and BTUs to KWHs)

Example, for me: 400 gal x 52 degrees x $0.08/KWH x 0.002444 =4.06
This is one cent different from above due to rounding off the conversion factor.

I was curious because I didn’t know if the cost would be $5 or $50 – negligible or significant.  For me, the difference between changing my water at 3 months instead of 4 months would be less than $10 plus chems per year.  The difference between changing at 2 months instead of 3 months would be less than $20 plus chems per year.  I am hoping that we can settle into a 3 month schedule, but we’ll see how things go.

[Zep]

very interesting information.....thanks Jet Sitter

personally i think it is way too much trouble/hassle to drain most hot tubs.
sure we all do it, it's not the end of the world
but neither was rolling up manual car windows
now most of us have automatic/electric car windows
one day most hot tubs will have automatic drain systems
as i have posted before i predict one day the industry standard will be to offer
a "push one button drain system" where a tub is drained without using garden
hoses, gravity or the clumsy sump pumps that may or may not still leave puddles
of water in seats, ect... i also think water issues are a hassle for many owners and
if it was extremely easy and hassle free more people would dump their water
more often and lessen the water quality issues.

[Swell-Tub]

Now you got me thinking I might drain my tub tonight to see what kind of experience it is. I plan on hooking a garden hose to the bottom adapter on my J-470. Then I will run the rose through my bedroom to the shower. In Vegas we have to drain all water to the sewer system for reclamation purposes. Then again I might just go home and sit in my recliner.

Scott  

[Calypso]

There are costs to not draining your spa. The more TDS you have in your spa and the other chemical cocktails make it tougher for your sanitizer to work so you have to use more sanitizer which costs more money. It is probably also tougher to balance Ph etc as time goes on which means more costs.

If you look at it this way refilling your tub is free

[Spatech_tuo]

I don't have the patience to read this thread with a fine toothed comb but it looks like part of the cost of the water is the sewer rate factored in. I hate to nip pick but I would never bother to send the water down the drain. I've always recommended people water their plants with that drained spa water by letting the sanitizer level drop before draining (it ends up being far lower than the amount of chlorine in the tap water).

[Jet Sitter]

Spatech - Good point about letting the sanitizer level drop and then draining to the plants and no need to apolgize about nit picking my lengthy post.  i wondered if it might be possible to drain to the plants instead of the sewer.  As far as costs go however, I will still be charged the sewer rate based on the number of gallons my water meter says I use, unless I have a separate "deduct meter" to measure water that will not end up in the sewer.  Many people actaully have these for their irrigation systems, but I don't.

Also I double checked my utility rates since I made the original post to find out if there would be an impact with paying higher rates for excessive use.  I found that my cost from the period from September 16 to may 15th would be as I calculated above, $9.70.  For the period from May 16th to September 15th, my total would be $10.12 due to a higher water use charge.  Still my cost on average will be less than $10 plus chemicals and the difference between the two rates is so small that I don't have to plan to do a fill on the last day of the low rate period.

[Jet Sitter]

Zep - I am a hard core "keep it simple" type and if I could have bought my last new car with roll down windows instead of electric I probably would have gone for it, but I would love a reliable automatic tub drain system.

[Zep]

"Zep - I am a hard core "keep it simple" type and if I could have bought my last new car with roll down windows instead of electric I probably would have gone for it, but I would love a reliable automatic tub drain system"  [/b]


LOL @ Jet Sitter......I think the auto-drain will start out as an optional because
most wont wanna pay the extra cost.....but just like electric windows I predict
it will become standard. Hopefully the free market will take care of it.....just
like rock facade side panels were offered by one or two makers now more
and more are starting to offer the same thing......if one of the major makers
starts offering a fully automatic drain system you can bet your booty the others
will follow suit thereafter once it shows it is causing them to lose sales.

[Jet Sitter]

Swell-Tub instead of a recliner you should be kicking back in that sweet J-470.

Calypso - I kind of got the impression that chemistry might get a bit more challenging the longer you go between fills.  The reason i was wondering about what it might cost to do a fill is becuase I think I'm going to be a prime candiate for chemistry struggles.

I have twin teen-age daughters who will definitely be having their friends over to get in the tub.  Add my teenage son and his buddies "Yeah Dad, sorry we didn't take a shower first before getting in after soccer practice - we'll be sure to next time" and you get an idea of what I am up against...

[Vinny]

I don't have the patience to read this thread with a fine toothed comb but it looks like part of the cost of the water is the sewer rate factored in. I hate to nip pick but I would never bother to send the water down the drain. I've always recommended people water their plants with that drained spa water by letting the sanitizer level drop before draining (it ends up being far lower than the amount of chlorine in the tap water).

Depending on where you live the amount of water used is considered going down the drain and your sewer bill reflects it. I used to live in an area that charged x # of dollars per 1000 gallons and y # of dollars per those same 1000 gallons. I now live in an area that charges a flat rate per year without any consideration to how many gallons are used. It might be something to consider if the cost is significant, I've heard some industries have seperate water meters for "drained" water vs everything else to be able to beat the cost of the sewer.

[wmccall]

I don't have the patience to read this thread with a fine toothed comb but it looks like part of the cost of the water is the sewer rate factored in. I hate to nip pick but I would never bother to send the water down the drain.).

In Columbus the sewer charge is calculated on 80% of your water usage.