# Thread: Inline water heater for spa-only?

1. ## Inline water heater for spa-only?

Hi all --- I have an inground pool with the spa that spills over, and I am looking for a simple way to heat the spa only. (Both pool and spa combined are 20K gallons, more or less).

I don't plan on spending much money on equipment, nor do I plan to heat the pool (only the spa, and that will be 2-3 times a week at most).

I was looking into inline water heaters (such as the one posted here).

Any thoughts on whether this is a good idea? I have no clue how hot/warm the water will get using this type of heater.

Op

2. ## Re: Inline water heater for spa-only?

Each kilowatt consumed will give you 3,412 btus.

Calculate the following:

gallons of water x 8.3 = pounds of water
pounds of water x desired temperature rise = BTU's required
BTU's required / BTU output of your heater = number of hours to raise the water temp to your desired temp

Most in-line spa heaters are 1.5 kw heaters = 5118 btus

A 300 gallon spa = 2490 lbs
2490 x 20 degrees = 49800 btus required (to go from 80 degrees to 100 degrees)
49800 / 5118 = 9.73 hrs, just to raise it 20 degrees
So.... 1.5 kw x 9.73 hrs = 14.6 kw/day. If electricity cost .11 cents/kw, it will cost you \$1.60 just in electrical costs of the heater, not counting in the increased pump run time.
(Edited to correct my math. I used the weight of water rather than the BTUs of the 1.5 KW heater - Thanks for pointing that out)

However, if you have a separate spa circulation system, you may be better off maintaining your desired temp and using a solar cover to retain most of your heat.

What a long way to say, you're probably better off using your gas heater and letting it run 15 - 30 minutes to get your spa water up to temp.

Now if cost of the heater was not a factor, you can consider small btu output heat pumps, which may cost up to \$2500. http://www.aquacal.com/index.php?option ... &Itemid=75

3. ## Re: Inline water heater for spa-only?

I get half the time than Poolsean - only 10 hours - still too much.

There are 3.780kg per gallon.
2.322 J/g*F

Without going into it all, the equation works out to:

t = 8.78*T*G/KW

were:

t = time in seconds
T = Change in Temp in F
G = Gallons
KW = Kilowatts

Here is a calculator
http://www.heateflex.com/html/techtools/TT3.html

Anyway, I have a spa connected to the pool sharing the same pump and opted out of installing a heat pump, which all the PBs do around here. I installed a Hayward Electric heater just to heat the spa.

http://www.haywardnet.com/aboveground/p ... eaters.cfm

It is small and uses hot water heater elements to heat the water. It is an 11 KW unit and can heat my 500 gallon spa 10 degrees F in just over an hour.

My wife and I use the spa pretty much every weekend, and as it starts getting too cold to go into the pool, we expect the kids will be playing in there during the daytime on the weekends too. What I've been doing is using our solar panels to heat the spa during the day on Fridays (we have a cover just for the spa). Even on cloudy days, because the spa is so small, the solar heats it up a good bit. So then when we use it during the weekend, the electric is there just to keep it warm while in use. However, even without the solar, the electric would be good for us. I'm currently installing a remote wall access panel to put the pump on a dial spring timer and buttons for turning on the heater and switching the valves. I'm going to wire it such that the heater can not come on unless the valves are set to spa mode and the pump is on. That way I can't accidently try to heat the entire pool.

4. ## Re: Inline water heater for spa-only?

From my limited experience (2 or so years) with spas, the use of a spa is not normally planned 10 hours or 20 hours in advance. Its normally either impulsive or maybe you get the, "Let's go in the spa in a little while"....

That being the case, I would suggest that any more than an hour or so to heat up a spa is not acceptable

With my gas heater, I can get the spa from 80 - 103 in about 23 minutes. Its about a degree per minute. Believe it or not, sometimes this seems like it is taking too long...

Good luck!

5. ## Re: Inline water heater for spa-only?

Originally Posted by mitch08
From my limited experience (2 or so years) with spas, the use of a spa is not normally planned 10 hours or 20 hours in advance. Its normally either impulsive or maybe you get the, "Let's go in the spa in a little while"....

That being the case, I would suggest that any more than an hour or so to heat up a spa is not acceptable

With my gas heater, I can get the spa from 80 - 103 in about 23 minutes. Its about a degree per minute. Believe it or not, sometimes this seems like it is taking too long...

Good luck!
Around here, (spa's for 23 years) it is usually impulsive. We have the inline spa heater. The times I have lowered the temp to low 90's have been a bummer even though the heater will take the temp up to 100 in less than an hour. We do use ours almost daily though, sometimes more than once a day.

In the summer heat, and with insulated top always on, it does, though, take over a day for the temp to lower even a few degrees with heater turned down, in the winter maybe half a day. So I don't even bother, any more, to take the temp down, as the heater probably isn't coming on much anyway. The insulated cover makes a huge difference.

My neighbor put in a beautiful IG pool, with included spa, with spill-over and a nice big gas heater for pool and spa. They have never used the spa and don't plan too (they use it as the "kiddie pool") for just the reasons of not wanting to heat it constantly so they can use it spur-of-the-moment. Occasionally, they come over and use ours when we are gone. (We house/animal sit for each other.)

gg=alice

6. ## Re: Inline water heater for spa-only?

Originally Posted by mitch08
That being the case, I would suggest that any more than an hour or so to heat up a spa is not acceptable
Aaah, Mitch, you are so right... but some of us have little choice in the matter. I enjoy getting in my in-ground spa when the outside temperature is flirting with 30° F. (That's late December and early January where I live.) No natural gas available in my subdivision... so it's electric heat or nothing. To raise the temperature of 750 gallons of 50 degree water to 100 and hold it there for an hour of soaking I must fire up my 18 kW electric heater a full 8 hours before we get in. Takes forever... and adds roughly \$50.00 to the electric bill for that single use.

If I could wind back the clock to the planning stage I would dispense entirely with an in-ground spa and use the \$8000 for an above-ground spa situated near the pool area where the tub can be heated round-the-clock and available year round for \$25.00 a month.

7. ## Re: Inline water heater for spa-only?

Just an FYI:

On a 120V portable spa, that picture shown would in fact be a 1500 watt heater. On a 240V system, it's 5500watts.

Scott

8. ## Re: Inline water heater for spa-only?

It just occurred to me to ask.... I'm totally unfamiliar with IG pools with spas. Can the spa circulation be separated from the pool circulation with spill over blocked some way? If so, it seems one could purchase (or have made) an insulated cover to keep the heat in. Or is this totally out of the question without major redo at the pumping station?

Having known and cherished the value of spa for so many years I would certainly look into that if I had a set up that seems typical for IG pools with spa. The psychological benefits are tremendous (relationship therapy) , but far outweighed by the physical therapy the spa offers.

gg=alice

9. ## Re: Inline water heater for spa-only?

Can it be done? Yes. Should it be done? No!

A hot tub has different sanitizing needs because the temp is higher. This energizes and will cause a gas off. That would cause the water in the tub to lose it's sanitizer and increase the free chlorine gas under a cover. That will kill an cover fast. Portable tubs use bromine or ozone so this doesn't happen.

Pool with attached spas normally get freshly chlorinated water just prior to getting to the pool. Some goes in the spa and the rest to the returns. Spill ways work, spa and pool stay sanitized and all is good.

Scott
PoolGuyNJ

10. ## Re: Inline water heater for spa-only?

Originally Posted by polyvue
Originally Posted by mitch08
That being the case, I would suggest that any more than an hour or so to heat up a spa is not acceptable
Aaah, Mitch, you are so right... but some of us have little choice in the matter. I enjoy getting in my in-ground spa when the outside temperature is flirting with 30° F. (That's late December and early January where I live.) No natural gas available in my subdivision...

We don't have gas lines out here either. My neighbors, like some others out here, put in a big gas tank, for their pumping station heater and to heat the new, huge addition they just added to the house and old part of house. (They have told me that their winter heating costs, for the house, have gone way down since switching to gas heat from electric.) One mistake they made, though, was to locate the tank so that the refill truck has to drive across their front yard to get close enough to hook up the the tank AND it seems, that the truck usually comes after it has rained.

If I could wind back the clock to the planning stage I would dispense entirely with an in-ground spa and use the \$8000 for an above-ground spa situated near the pool area where the tub can be heated round-the-clock and available year round for \$25.00 a month.
Yeah, I'm so glad the above ground spa was our only choice as the pool was here when we move in. We are totally electric, too. I'll bet it doesn't cost much more than \$25-\$50 a month in electricity to keep it heated and we run the circulation (filter and heater) 24/7. Our spa is located on the north corner of the deck. The blasting winter winds come up the valley from the plains, so we have a huge wind chill factor during most of our short winter.

11. ## Re: Inline water heater for spa-only?

Originally Posted by geekgranny
It just occurred to me to ask.... I'm totally unfamiliar with IG pools with spas. Can the spa circulation be separated from the pool circulation with spill over blocked some way? If so, it seems one could purchase (or have made) an insulated cover to keep the heat in. Or is this totally out of the question without major redo at the pumping station?
My IG spa w/spillover shares plumbing with the pool. It can be isolated by turning a valve, which is done when I'm heating the spa by itself -- but this is really a compromise: the in-ground PVC pipe runs and shared pad plumbing and filter will add many gallons of cold water to a spa that has been previously heated so unless one is prepared to forego filtering of pool water between soaks, having an IG spa at a ready temperature is nigh impossible. To add to this difficulty, the equipment pad's air feed will dramatically cool down a spa in cold weather once the jets are turned on.

I was amused at your description of neighbors having a truck drive across their lawn to replenish a gas storage tank... newer middle-class homes built in suburban California wouldn't have enough room to park a truck, nevermind drive one in their front (or back) yards. That's also the reason why I couldn't install a propane tank; there's just not enough setback from neighbor's fences/homes.

12. ## Re: Inline water heater for spa-only?

Originally Posted by PoolGuyNJ
A hot tub has different sanitizing needs because the temp is higher. This energizes and will cause a gas off. That would cause the water in the tub to lose it's sanitizer and increase the free chlorine gas under a cover. That will kill an cover fast. Portable tubs use bromine or ozone so this doesn't happen.
Are you certain about this? I used Dichlor granules exclusively in my above ground Hot Springs spa for more than 15 years and I don't believe that the outgassing you describe had a detrimental effect on the cover. I could be wrong, of course -- the cover did eventually need replacing but it was the top seams of the cover that disintegrated first, from UV/weather exposure. At that point the cover was at least twenty years old.

13. ## Re: Inline water heater for spa-only?

I am sure. This is for spas without an ozonator. They should use bromine as the main sanitizer and non chlorine shock.

DiChlor also adds stabilizer to the water too so the chlorine will stay longer than what I consider normally desirable. I prefer, with portable tubs that are equipped with an ozonator such as your Hot Springs, to use Lithium Hypochlorite as the preferred chlorine shock. It dissipates quickly after shocking and the cover can be put back on sooner.

Spas get their water changed more frequently so an accumulation of CYA isn't normally a problem.

Scott
PoolGuyNJ

14. ## Re: Inline water heater for spa-only?

Wow, I didn't think that this would turn into such a hot topic!

Very good points made across the board. Somehow, after floating my options, I think I may be leaning toward getting a few solar panels, rather than spending \$2K for a high KW heater, or spike up my power bill (I live in Orlando, the AC already does that 7-8 months out of the year). The average water temperature during winter is 55-60F, and 84F during the peak of summer. I figure if I can get the water temp to 78-82F with 2-3 solar panels, then I'll be OK with that.

I also don't want to run two separate systems for the IG pool and spillover spa, so I suppose that, by using solar, I would have to warm both pool and spa.

I still don't know how many panels I should get. Would that all depend on how warm I want the water/how cold winters get?

15. ## Re: Inline water heater for spa-only?

Originally Posted by op999
Wow, I didn't think that this would turn into such a hot topic!

Very good points made across the board. Somehow, after floating my options, I think I may be leaning toward getting a few solar panels, rather than spending \$2K for a high KW heater, or spike up my power bill (I live in Orlando, the AC already does that 7-8 months out of the year). The average water temperature during winter is 55-60F, and 84F during the peak of summer. I figure if I can get the water temp to 78-82F with 2-3 solar panels, then I'll be OK with that.

I also don't want to run two separate systems for the IG pool and spillover spa, so I suppose that, by using solar, I would have to warm both pool and spa.

I still don't know how many panels I should get. Would that all depend on how warm I want the water/how cold winters get?
Well after having third thoughts (realized that the benefits of solar would only extend my swimming season a few weeks at most, and it mean covering a significant portion of the roof in panels), I think I've gone back into this setup, but only for the spill-over spa. (My spa runs on the same system as the pool, which means I would have to switch back and forth, and not be able to keep the spa warm.)

I saw one similar to the one of the pic I posted above; it was rated at 5.5Kw.

So now the mission begins!

16. ## Re: Inline water heater for spa-only?

A 5.5KW spa heater is intended to a portable tub like a Jacuzzi. These tubs are normally maintained at temperature after the initial fill. It usually takes running overnight to get where they are desired. It would take a lot of hours to heat the spa attached to the pool.

Solar would be a similar situation in that it would take a long time time to heat and reheat the spa's water.

Have you considered a small propane heater, say a 100 to 150K BTU that will do the job in 15-30 minutes? Then it would be ready when you are. You can expect them to use, at this size, about a gallon an hour of propane when fired up and less when it's set temp maintaining temp, i.e. when you're in it. When you're done, turn it off and reset your valves to normal pool mode.

I painted my tanks and have ivy growing up the sides so they aren't sticking out like sore thumbs.

Hope this helps.

Scott
PoolGuyNJ

17. ## Re: Inline water heater for spa-only?

Originally Posted by PoolGuyNJ
A 5.5KW spa heater is intended to a portable tub like a Jacuzzi. These tubs are normally maintained at temperature after the initial fill. It usually takes running overnight to get where they are desired. It would take a lot of hours to heat the spa attached to the pool.

Solar would be a similar situation in that it would take a long time time to heat and reheat the spa's water.

Have you considered a small propane heater, say a 100 to 150K BTU that will do the job in 15-30 minutes? Then it would be ready when you are. You can expect them to use, at this size, about a gallon an hour of propane when fired up and less when it's set temp maintaining temp, i.e. when you're in it. When you're done, turn it off and reset your valves to normal pool mode.

I painted my tanks and have ivy growing up the sides so they aren't sticking out like sore thumbs.

Hope this helps.

Scott
PoolGuyNJ
Hi Scott-- actually, not, but now it's on my mind. I've seen a couple for sale, but the thought never crossed my mind -- until now. One has a 120 V connection, and has 118K BTU. (It does not come as a 220v). Do these use your standard grill-type of tanks? Or would I have to install a larger tank. (I know nothing about the larger tanks, connections, etc.)
Thanks for the tip -- Omar

18. ## Re: Inline water heater for spa-only?

Typically, a larger tank is called for. A copper line is then run from the tank to a pressure regulator to reduce the pressure/amount of gas used. A heater the size you mentioned can expect to use about a gallon of propane per hour of operation.

Tanks are filled to about 75 to 80% of capacity to allow for expansion. A 125 gallon tank would get 100 gallons. I would expect that that would last quite a while. The tank should be within 100 feet of access to the filling truck. They can only carry so much hose and the driver can only drag so many feet before the weight is too much.

The tank can feed the heater from quite a distance. A second regulator may be needed so that the bulk of the distance from the tank to the heater( buried) can be done under a somewhat higher pressure to ensure an adequate supply is available. The longer the run, the bigger the loss in terms of pressure, just like pool plumbing.

Scott
PoolGuyNJ

19. ## Re: Inline water heater for spa-only?

I have a fairly antiquated gas heater (Gemini 3) and I use it to heat the SPA only by blocking the jets in the pool with simple rubber stoppers and forcing the circulation of the water in the spa only. Not a perfect solution but it does heat up the Spa by about 10 degrees per hour.. Almost \$20 per use but worth it!!

I have been looking into upgrading the heater to something more efficient but the upfront \$ cost is hard to justify...

20. ## Re: Inline water heater for spa-only?

I'm not intending to be mean or silly. If the pool/spa system causes so many problems, issues, and financial costs if one wants to use it as a "real" spa, why do builders and/or owners continue to do this combination? Are owners lead to believe by PBs that they will have a heated spa to enjoy whenever they want? I just don't understand.

gg=alice

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