Gas heated hot tubs?

[Grumman-581]

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...

[R. Lamar]

Gas heating of a hot tub is far cheaper than electicity. I have done my homework on this issue and have found your info to be incorrect in my region of the world. I can also get longer life from a natural gas heater versus the electric heater supplied by the tub manufacture. This results in less money spent on maintenance. I am a master plumber by trade and am currently involved in purchasing a natural gas hot tub system or building what I want. I would love your input on tub manufactures and heater manufactures. Who knows, I may even start my own natural gas hot tub company.

[NotMe]

Neighbor has a electric hot tub. We have a NG hot tub heater that does the pool as well. I can heat the poll and hot tub for less than the neighbor spends on his hot tub alone. End result we get three +/- months extra use of the pool each season (N Texas).

[trader_4]

I don't believe it's possible to realistically heat an entire swimming pool with nat gas for less than it costs to heat a hot tub. Typical pool has 100X the water that a hot tub has. I have an electric hot tub and don't even notice it much on the electric bill. I don't keep it hot all the time, I turn it up before use. But even if you kept it a 100F, it's fairly well insulated. A pool is not. Folks here in NJ have gas bills in the thousands if they try to heat a pool. The freaking heaters are 300 - 400K BTUs. I don't spend that much on the entire house electric bill. The whole thing in winter, hot tub included is $140. The typical hot tub heater is maybe 8KW. Even though electric is the more expensive fuel, the amounts of energy it takes are vastly different, ie a 40,000 gallon pool and a 400 gallon insulated hot tub.

[gfretwell]

I have an 11kw spa heater and it costs $1.54 an hour to run. I get about 10 degrees an hour when I am heating it up.

We assume it costs us about $5 every time we use the tub, typically a few hours at a time. I have solar collectors that I can switch over to the tub and that easily cuts the heating time in half, starting from warmer water but now I have some trees that are encroaching on my solars. It is fixn to be chain saw time.

[trader_4]

That sounds reasonable. It obviously comes down to how many times you use it. Here, it typically only gets used a couple times a month, so it's not that noticeable in the electric bill. It also depends where you have it located. In a previous house, I had one inside and that makes a big difference.

I think you'd agree, even if it cost $100 a month in electric, there is no way you could heat a swimming pool plus spa using nat gas in that same kind of environment for anywhere near $100. If it cost $100 to run a hot tub here in NJ with electric, it would cost $1000 in nat gas to heat a swimming pool. Unless you're talking about just raising the temp of the pool by one degree or something. And then you have the huge loss of heat from a pool compared to the far less loss from a well insulated hot tub.

I think solar can work well for pools, provided you have enough room for the collectors and don't mind what they look like on the roof or someplace on the ground. I'm kind of surprised that with what it costs to heat pools, I don't see any here in NJ. It would extend the season by a month at the beginning and end and keep it more comfortable the rest of the season too. You would think people just don't care, but then they put in new pools with nat gas heaters here all the time. I only know a few people who use the gas heaters though, for obvious reasons. It's also funny because instead of the dopey nat gas heater, that involves not only the cost of the heater, but also running gas lines, possibly resizing the meter, etc, you could pay for most of the solar install and after that it's almost free.

[NotMe]

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.

[gfretwell]

My wife runs a country club with 7 heated pools, heat pump/electric. I can get the bills if anyone is interested. They still have a real hard time getting much more than 10 degrees above ambient air.

Solar heaters work well if you cover the pool but uncovered you will only get 8-10 degrees above ambient air with a collector area the same as pool area. The main problem is how much heat you lose at night without a cover. My neighbor has more collector than pool and a cover. She can make it uncomfortably hot on all but the coldest days (in South Florida) They normally say collectors get you a month on each side of the season ... here. YMMV up north.

[gfretwell]

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.

[trader_4]

Yes, that's what I've gathered from what I know about solar too. A lot of heat is lost at night from the surface. But the downside is I would think taking the cover on and off is a pain, plus the pool with a cover is going to look ugly. And maybe if you have leaves and stuff, that can blow onto the cover, that becomes a pain too. But if you can get 8 deg without a cover, that's not bad. It would be enough to level out the temp all of the regular season here in nyc area and would extend the season by probably two months, ie a month on each end.

[trader_4]

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.

[NotMe]

Heat pumps are effective/efficient within a comparatively narrow range and basically worthless if the ambient air is below 40 F. Likewise heating water to 100F is with a heat pump also techniclly difficult.

[NotMe]

Unglazed collectors?

[gfretwell]

Regular pool heat collectors as opposed to a collector with an enclosure around them.

[Denis]

replying to Jeff Guay, Denis wrote: YES you can they see them with Natural gas or Propane see

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.

[Helene]

replying to NotMe, Helene wrote: Did you. Just. Buy and electric and convert it to gas