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Typical Water Loss


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#1 Tubber McGee

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Posted 31 January 2011 - 09:02 AM

Hello,

Just curious as to how much water you lose due to evaporation - getting in/out - splashing! (minimal splashing)

Seems like I have been adding about 5 to 10 gallons per month due to the water level going down!

When my new tub (HS Vanguard) was delivered in October - I had a fitting that was busted and fixed. Just want to make sure this is about normal and I do not have a small leak.

How often do you add water and how much?

Thanks

#2 spatech (the unreal one)

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Posted 31 January 2011 - 10:06 AM

Hello,

Just curious as to how much water you lose due to evaporation - getting in/out - splashing! (minimal splashing)

Seems like I have been adding about 5 to 10 gallons per month due to the water level going down!

When my new tub (HS Vanguard) was delivered in October - I had a fitting that was busted and fixed. Just want to make sure this is about normal and I do not have a small leak.

How often do you add water and how much?

Thanks


You left out a key part of the equation; how much are you using the spa and how many people?

With regular use thats not a shocking amount. With light use I might worry that you're losing it too quickly.

#3 Tubber McGee

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Posted 31 January 2011 - 10:18 AM

Thanks SpaTech!

The tub is currently being used about 5 times per week! Usually just me - the whole family (5 of us) once or twice a week!

What exacty is causing the water loss? I know this is silly question!

Thanks

#4 footie

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Posted 31 January 2011 - 10:24 AM

Thanks SpaTech!

The tub is currently being used about 5 times per week! Usually just me - the whole family (5 of us) once or twice a week!

What exacty is causing the water loss? I know this is silly question!

Thanks


I got mine last summer and my water loss was small back then but during the height of winter it got heavier, I'm wondering if this is a case of more evaporation due to greater difference between the air temp and water temp during winter.

Any idea?

#5 Roger

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Posted 31 January 2011 - 10:34 AM

Hello,

Just curious as to how much water you lose due to evaporation - getting in/out - splashing! (minimal splashing)

Seems like I have been adding about 5 to 10 gallons per month due to the water level going down!

When my new tub (HS Vanguard) was delivered in October - I had a fitting that was busted and fixed. Just want to make sure this is about normal and I do not have a small leak.

How often do you add water and how much?

Thanks


Take a swim suit out to the tub and dunk it in the water. Then ring it out over a bucket. Do this as many times as you use the tub and see how many gallons you have. Then consider evaporation. Depending on the temp difference between the ambient air temp and your water??? You never mentioned where you live? Is it real steamy? 5-10 gallons could be normal. Seems to me that's about how much I added in the winter (colder months) when I maintained a tub full time.
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#6 Hillbilly Hot Tub

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Posted 31 January 2011 - 11:37 AM

In the winter I bring a gallon jug of water out with me because i know this is about what i am going to loss at each use. It saves me from dragging the hose out every few weeks to top off the tub. With swimsuits, i would lose even more water, and bring out 2 gallons at each use. My tub never needs to be topped off doing this, and no...I have no leaks.
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#7 hd2000

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Posted 31 January 2011 - 01:40 PM

I'm probably adding about about 8 gal or so per month in the winter time. In the summer, it's less. I don't know exactly why, but I suspect it has to do with the difference in air temp compared to the heated water temp. I think if the water in the tub was colder, it would evaporate less, but I'm guessing. Throw in relative humidity somewhere in the equation.

#8 drylandfarmer

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Posted 31 January 2011 - 01:49 PM

I am losing around 3 inches water every 2 weeks. Topping it up every 2 weeks. Temperatures outside are very cold creating a lot of steam. Using the tub daily for about 1 hour each time. No leaks that I have found so assuming most of it is evaporating.

#9 Jake the dog man

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Posted 31 January 2011 - 02:56 PM

I add about an inch of water every 6-8 weeks. It gets used 2-4 times a week, year round.

#10 chem geek

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Posted 31 January 2011 - 07:03 PM

For those that are interested, the fairly standard formula for evaporation rates for pools that probably applies to spas as well when they are uncovered is the following:

Evaporation (inches/hour) = (4.8824/25.4)*(69.4+30.8*WindInMPH)*(SatVapPress - VapPressInAir)/(1.7988*(597-(597-540)*(WaterTemp/100)))
where
SatVapPress (inches Hg) = (0.0075006/25.4)*100*6.1121*EXP(((18.678-WaterTemp/234.5)*WaterTemp)/(257.14+WaterTemp))
VapPressInAir (inches Hg) = (0.0075006/25.4)*RelHumidity*6.1121*EXP(((18.678-AirTemp/234.5)*AirTemp)/(257.14+AirTemp))

So you can see that the evaporation rate depends on two primary factors: the amount of wind and the difference between the vapor pressure of air at the water's temperature minus the actual vapor pressure (water content) in air at air temperature. Remember that warmer air holds more water so has a higher saturation vapor pressure. Therefore, unless the air is at 100% relative humidity AND at the same temperature as the water, then evaporation will occur.

Evaporation occurs more rapidly when the air is dry (i.e. relative humidity is low) and when the water is warmer. Aeration from the jets acts somewhat like wind. 1 gallon removed from a 350 gallon spa would be equivalent to evaporation of around 0.14 inch. Even if the air was completely dry with no water content at all, evaporation with no wind from a 104ºF spa is only 0.03"/hour. However, with a 5 MPH wind it's 0.09"/hour and a 10 MPH wind it's 0.15"/hour (i.e. one gallon per hour).

#11 footie

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Posted 01 February 2011 - 04:10 AM

I never actually notice the water drop on my tub because of the slave tank under the main tank (Cascade model), the only way for me to see it is remove the pump panel (simple) and view the clear tube that has recommended levels for occupancy. But I generally add more at winter than summer so reckon evaporation is higher during the cooler months.

#12 Hotsprung

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Posted 01 February 2011 - 05:18 AM

I found I was putting quite alot in until I started lifting the cover from both sides and allowing the condensation on the underside to drain back in to the tub, before opening it normally. This has halved the amount I need to top up.




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