Gas heated hot tubs?

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Without going into the thermodynamics the pool is ~ 10K gal, the hot tubs closer to 1000 gal. (~10:1) Additionally the delta T for the hot tubs is greater than the delta T for the pool. (a key element is the surface area of the pool vs the surface area of the hot tub)
For some reason both my system and the neighbor's system are metered separately than the rest of the house. Additionally we have exceedingly low NG rates and a 'competitive' electric provider system in Texas (means electric power users are royally screwed by games the power companies play.)
The exact details don't matter as we (both retired engineers) have compared numbers over drinks too many times. He'd make the conversion ri NG but the permitting and other cost are too great to justify the expense.
BTW again without going into the thermodynamics an in-ground pool is very well insulated especially considering the typical above ground hot tub.
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That is a tiny pool and a huge hot tub (like one of those 10 person Hotel tubs)
My pool is 15,000 gallons with around 500 sq/ft of surface area and the 8' (OD) octagon tub is about 350 gallons and 45 sq/ft area. That makes the area to volume ratio a lot worse in the hot tub. The big difference is it is a lot easier to cover a hot tub and that cover can have a pretty big R value. You still run into the problem that unglazed collectors will not get you a very high delta over ambient air even with a well insulated tub. If you used glazed collectors you could get the McDonalds coffee hot.
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On Tuesday, March 3, 2015 at 7:37:44 PM UTC-5, snipped-for-privacy@aol.com wrote:

I agree, it's not typical that's for sure. And I think he said they are shared by the same heater? Around here you only see that on inground pools and not in that size ratio. The 10,000 gallon pool is like an above ground and many of those are bigger than that. I would think most home hot tubs are ~500 gallons.

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wrote:

Unglazed collectors?
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Regular pool heat collectors as opposed to a collector with an enclosure around them.
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I'm not a hot tup owner nor have I ever been. You leave the same water in all the time, like a pool? Or, do you fill it like a tub? If you fill it, like a tub, why couldn't you just tap into a regular HW heater on an on demand heater (Even better for this application) and fill it up. Then just use the elec to maintain the temp. I suspect the cost of the water is nothing compared to the cost of keeping it hot on an ongoing basis.
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hot tubs generally kewep the same water all the time... kinda gross if you ask me.
jacuzzi bathtubs get filled and emptied after use a much better arrangement
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Thats kind of what I thought - Why not use it like you would a jacuzzi? Fill it every time? I would assume it has a gravity drain. That coupled with your favorite NG demand (Tankless) water heater and then you only need 'lectric to maintain the heat while you are using it. Why am I even commenting I know sh** about hot tubs.
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No wrote:

Because they can take 250 gallons of water and it will take quite awhile to fill it each time it's used for one. Then there is the issue of having the correct water chemistry, unless you want to get in a tub with multiple people and no bromine disinfectant. At least with the chemicals I use it takes hours to establish the correct level. They are insulated, so unless it's a long time between uses, it's going to take more energy to warm up 50 degree water every time you use it, plus if you use it 4 times a week, that's 48000 gallons of water a year compared to maybe 1500 gallons. And then there is the problem of what to do with it in parts of the country that get below freezing in the winter. Full and with heater maintaining even a lower temp, it won't freeze. But if you drain it, now you have to fully winterize it, which means getting all the water completely out, which isn't that easy on some units.
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Even a relatively small hot tub holds about 250 gallons. Draining it is not at all like draining a bathtub, either. It's not hooked up to the house plumbing, so you need a place for all that water to go. There will always be a gallon or two of water that must be bailed and sponged out of the very bottom. It also means taking off an access cover to drain it, and blowing compressed air through all of the pipes to clear them so nothing grows in them while dormant. When you refill the tub, you would also have to bleed the plumbing. It's not that hard to do a few times a year during normal water changes, but draining and filling a hot tub between each use would be moronic.
It's not a problem to keep it sanitary, and it's not expensive to keep it heated.
You change the water about 4 times a year depending on usage and other factors.
Finally, having used both a jacuzzi and a hottub, I can tell you that a jacuzzi does not give anywhere near the same experience. It's a pretty poor second place at best.
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On Thu, 30 Mar 2006 16:25:41 GMT, Mys Terry

The chemicals used in a hot tub, chlorine, bromine, ozone, etc. are used to kill that bacteria that might otherwise form from keeping a standing body of warm water for an extended period of time. The human body sheds a layer of skin while bathing and filtration is necessary to collect this and the other organic solids that will otherwise collect in the water.
If you pay for city metered water, the expense of filling up a 250 gallon hot tub every other day would quickly add up. Also to bring that much water to an operating temperature of 101 F would be high compared keeping the tub at some standby intermediate temperature and just applying heat to make up for the losses.
Beachcomber
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It's not unusual for an in ground spa to have gas heated water. It's unusual for this heat in a hot tub, however. Gas heaters are fairly expensive, require piping for the gas and are large enough that they don't fit inside a hot tub enclosure. A small gas pool/spa heater is probably around $1200, where an electric immersion heater is around $200.
That said, because the electric heater is nowhere as powerful as even a small gas one, it is customary to keep hot tubs heated 24/7. Otherwise, it'd take a day or so to reach temperature. With an external gas heater, you could fire it up a half hour or less before getting in and have great hot water. That sways things in favor of a gas heater, if you want to save on operating costs.
At a mountain cabin we owned, I had a hot tub with an electric heater. Since LP was nearby for our furnace, I considered getting one of the smallest LP- fired gas heaters and using it as the primary heat source, with the electric heater merely being used to keep the water at 40f to prevent freezing.
Frankly, in my younger days, I'd have considered buying a domestic gas-fired water heater in the 30-gallon range and hooking it to the the hot tub, using a circulating pump. I'd have built a little enclosure for the water heater to protect it from snow and rain. I'd have kept the electric heater for backup or for when I would have shut the gas system down to prevent freezing when we'd be away for several weeks.
Pardon me. It's happy Hour here, and I have a 100f in ground spa awaiting me and my martini.
Mark
Beachcomber wrote:

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To handle the concerns about whatever disinfecting chemicals you might have in your hot tub possibly affecting your water heater, you could design a closed loop heating system where the water from the water heater goes through copper pipes in the hot tub, but do not acutally merge their water with the hot tub water... Presurize this right and you could have water hotter than 212F going through this loop... Of course, if you're going to go to all this trouble, you could just design your own heating element out of a coil of copper pipe in an enclosure with a burner at the bottom... Make it a multiple layer coil with the cold water coming in a the top, thus it would pick up some of the heat that would be escaping the flue... The warm water would come out the lower portion of the tube closest to the flame... Since copper tubing would not be all that expensive considering the length of life you would probably get out of it, you wouldn't really be that concerned with whatever disinfecting chemicals might be in the water, so you wouldn't need to go the route of a close loop heating system... I designed something similar to this to provide hot water for showers while camping... It used a standard commercial fish fryer gas burner with a propane tank for the heat source... It beat the 'ell out of taking a cold shower...
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On Thu, 30 Mar 2006 23:48:59 GMT, snipped-for-privacy@notreal.none (Beachcomber) wrote:

???
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replying to Jeff Guay, Denis wrote: YES you can they see them with Natural gas or Propane see http://forestlumber.com/barrel-hot-tub-kits /
Gas Heated Packages * Tub with stainless steel hoops * Deluxe full circle benches * 100,000 btu Hayward H series gas heater, electronic ignition specify propane or natural gas, indoor or outdoor * 1 1/2 hp 2 speed pump, spa side speed control (customer supplied GFCI is required) * 4 jets, 2 air controls, 2 high volume suctions, 25 sq. ft. cartridge filter * All hose, plumbing fittings are included and most have been pre-glued * Floating thermometer * Insulating 4″ foam/vinyl cover with locking hold down tabs (available in 9 colors)
Size 5×3 …………. 7058.00 retail price Can $ 5×4 …………. 7561.00 6×3 …………. 7570.00 6×4 …………. 8137.00 7×3 …………. 8098.00 7×4 …………. 8718.00 8×4…………..10,233.00
Prices are subject to change without notice.
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