Spa (Hot tub) Renovation - Gas? Solar?

[Please invert everything left]

I've just inherited a working 8' wide spa (AKA hot tub), fiberglass body in a foam-insulated wooden frame with an insulated lid, holding about 700 gallons. We're going to install this outside on what was a small (non-reg.) basketball court, and put up a windbreak around it.

My county's building code requires a separate circuit to feed the 200A 240V draw of its control panel (AKA 'pack'), dual-stage pump and electrical heater. Installing that circuit, and the new panel it would require (as the existing panel can't handle it) will cost $2,400, as per two estimates from reliable electricians.

A hot tub manufacturer's website estimates it will cost $380/year a) to run the pump on low by timer to keep it clean, b) to run the pump on high when we're in it, and c) to heat it to the temp most folks like. That assumes our electrical rate is at its current 8.4 cents per KWH.

Has anyone here reworked a similar hot tub for gas heat? Or, for solar?

Natural gas and LP gas are much less expensive to heat with here (our electric utility is owned by Enron, happy, happy, joy, joy), and if I can replumb it to use an on-demand heater,

heater would cost less than $800 and pay for itself in five years. It also would reduce the size of the electrical install; I wouldn't need a separate circuit and therefore would not need a new electrical panel.

I've also seen the Real Goods solar heating system. The Real Goods rep said his Portland customers still need some heat in the coldest month or two, but the rest of the time, no heat is required. This $1,900 (incl. motor freight) system is said to be user-installable:

It would be nice to use the existing control system ('pack') but those can be had for

[John Grabowski]

Are you sure about the 200 amp load? That's a big circuit for a portable hot tub. Usually they are either 20 amp or 50 amp depending on the heater

John Grabowski

and could allow us, with pump replacement, to go 110V completely:

tape - Richard Preston, THE COBRA EVENT.

[Please invert everything left]

-- Nobody but a fool goes into a federal counterrorism operation without duct tape - Richard Preston, THE COBRA EVENT.

[Jeff Cochran]

200A? That's a *huge* heater and pump. Normally a spa that size might hit a 50A or 60A circuit.

Well, for a 200A circuit that may be about right. But even still, you could reconfigure with a standard 50A controller, heater and pumps for less than $500, and *maybe* another $500 to run the new circuit.

Gas heat's no big deal, but you still have pumps. You'd need to buy the gas heater and controller, but they're available for retrofit anf may even have been an option on your model.

Solar is a waste for a spa. Can't provide enough heat rise and pretty much sucks ofr a midnight soak.

Jeff

[Jeff Cochran]

Okay, 40A and you can't pull it from an existing panel? Even the average home on a 150A main would likely have no trouble with a 40A spa.

But if those are the figures, I'd go with gas. Actually, I'd skip the spa and look at upgrading my electrical service anyway.

Jeff

[SteveB]

I keep my spa at 99 or 100. I can't imagine 105, and think that might even be dangerous. I have a 220v. spa, and it raises the temp of water 5 degrees F per hour. From 80 to 100 would take four hours of having the 220 on. I believe it is less to just set it at 99, and the spa kicks on and off to use less power. Anyway, that's the way I do it. Might not be the most efficient, but it works for me. It is always ready to go jump into. Now that the cooler weather is here, today is a draining day and refilling day.

I have considered a wood fired copper coil system for a mountain cabin, but it would take a bit of preparation and maintenence. Not really worth it unless you are living there long enough to justify it. Might work for a home spa, but it would just get pricey and complicated IMHO. I'll stick with the old reliable 220v system, thank you.

Steve

[Greg]

I tried it. 50' of 3/4 copper coiled in the top of a 55 gallon drum. I tried wood and coal. It works but it isn't as hot as one would think and controlling temp is hard once you get it hot.

[SteveB]

I had also considered it for a Rube Goldberg type of hot water heater. A couple of years back, I was considering a plot of land in the mountains, and checking out systems. There is a lot available in 12v. lighting, propane refrigeration, 12v. water pumping systems, etc. But HOT water was something of a bear in large quantities.

So, I got a 38' motorhome instead.

STeve

[Greg]

This thing would boil 30-40 gallons of water pretty quick, certainly fast enough to supply normal hot water needs but when you have 300 gallons in an open tub it takes a lot to make a difference. If you put the tamk above the heater you would not even need a pump. It would thermal siphon up there. Make damn sure you have a pop off valve so it doesn''t blow up on you.

[Greg]

See me in the spring. I am fix'n to try it. My real objective is pool heating but I am going to dump the hot water in the spa and then the pool. (from glazed collectors) My results are not going to transfer well if you are in Frostbite Falls Minn tho. I am in south Florida. This is really more of an experiment than a plan. I know I can buy myself about

10 degrees in the pool, I am just going to see what the spa does. If the solar doesn't work I do have 11kw of heat.

BTW if gas is cheap where you are it is a good option. My 11kw (a lot more than most spas) is only about 37,000 btu. A decent gas heater is well over

100,000btu.

[Pam]

and could allow us, with pump replacement, to go 110V completely:

I converted a 1986 Sundance fiberglass spa by making a woodstove heat the water and use thermosyphon effect to circulate the water. No jets, no electric, but I go away during the winter, so it doesn't get used when there would be freezing temp(I drain it). It has a good cover(really important) and heats up fairly quickly when needed with about 1 1/2 cubic feet of pinewood. If I didn't have a wood supply, or wanted to use it in cold times, I would bring in the 220 volts of electricity, get the BEST cover for that model, and enjoy! Stretched out over say 4 years your investment would cost you about the equivelent of one seat at the movies a week, and I have never relaxed that much at a movie!

I used to make the newbies bring me a case of beer and firewood for using the tub, until I had so much of both that I couldn't park in my garage, now I just let them make a donation if they want, might help you defray your start-up costs if you did something similiar. Never had a complaint about nudity, either, all my neighbors love to soak in my backyard.

positively yours,

Pam

[Chet Hayes]

What you're doing in south FL sounds reasonable for many reasons:

Your spa is part of a pool, so the solar heat installation is saving not just the spa energy cost, but the pool heating costs, which are much larger than the heating costs of a typical stand alone home spa.

The climate is ideal

You have backup heat available

You're approaching it as an experiment, not a recommendation for someone seeking to avoid the cost of a 240V line for a stand alone spa.

I would also agree that gas is a good heat source for an inground spa/pool combo like you have. However the OP has a typical small stand alone spa. I've never seen one of these offer gas as an alternative heat source. The gas heaters are all seperate high capacity units, for applications like yours. I think gas is just not practical for these types of spas due to issues like, could you fit one inside the spa, where would the exhaust gas go, having to run gas lines, etc. The cost savings are just not worth it, for the amount of energy used, which is why manufacturers don't offer them. And trying to backfit one into an existing spa with an electric heater is a lot more cost and trouble than it's worth.

[Greg]

Most manufactures use a generic "skid pack" that they don't make. It is just a quick way to get the product to market and avoid U/L listing issues. The main downside of using gas for a spa heater is the initial cost. Once it is installed the people I know who have it, love it. You can bring up a cold spa to 102 in 20 minutes or so. The cost savings comes on 3 levels. You use less chemicals in a cold spa, you don't have to pay to heat it when you aren't using it and gas is usually cheaper than electricity. You will have to rationalize that against a heater that may cost 3-4x what an electric one costs but if he needs a $1000 service upgrade to hook up electric that cost may be a wash.

[Astro]

Sorry Don,

I must be totally daft - what are you talking about?

All I said is that Nick's argument that temperatures in the low 60's with high humidity would feel cold is right. Any psychometrics table supports this.

As for what you're saying below - of course humidity is tightly controlled in many environments! I must have missed the threads where he's arguing that it isn't. Can you point to some specifics? I searched already but only found the raging debates with Turtle regarding the comfort levels at various RH's.

What am I missing here?

[Astro]

okee-dokee. Thanks for the background. It's good to know more about the players and history in these discussions as I get more involved in the field.

Cheers.

[nickspam]

I denied that. Humidification raises fuel bills, even with a lower thermostat setting, unless you live in an extremely airtight house.

Nick

[nicksanspam]

ASHRAE 55 says a 48x48x8' house with R20 walls and ceiling would be equally comfy at 69.4 F and 20% RH or 68 F and 50% RH. If it's very tight, with 0.5 air changes per hour, would "proper" humidification to 50% save energy?

G = 48'x48'/R20 + 48x4x8/R20 = 192 Btu/h-F, so dropping the room temp from 69.4 to 68 F saves 1.4x192 = 269 Btu/h. At 69.4 F and 20% RH, Pd = 0.2e^(17.863-9621/(460+69.4)) = 0.1466, approximately, with wd = 0.62198/(29.921/0.1466-1) = 0.003063. Air at 68 F and 50% RH has wh = 0.007347. With 0.5x48x48x8/60 = 154 cfm of air leakage, humidifying from wd to wh requires evaporating 154x60x0.075(wh-wd) = 2.96 pounds of water per hour, which requires about 1000x2.96 = 2960 Btu/h of energy, so the net "savings" is 2960-269 = -2691 Btu/h, or minus 64.6K Btu/day, costing about $1/day more with oil heat or $2 per day with electric heat.

I've done these calcs several times now. HVAC people tend to forget that evaporating water takes heat energy, even if a humidifier belt uses little energy by itself, and that heat energy has to come from somewhere. And we often get into discussions about health and furniture, vs energy and forget that caulking a house (vs humidification) can raise the indoor RH while SAVING on fuel bills.

Nick

[Serendipity]

But, too dry of indoor air causes all types of health problems such as mucosal membrane irritation, nose bleeds, increased viral infections, and more. Further, improper indoor humidification dries out wood furniture and the house itself causing wall cracks and worse. So there has to be a proper balance of humidity.

[Nick Pine]

And we often get into discussions about health and furniture, vs energy, and forget that caulking a house (vs humidification) can raise the indoor RH while SAVING on fuel bills.

Nick

[Joel M. Eichen]

Humidifier ........ or a pot of water on the wood stove!