Cheapo hot tub critique needed.

[torlissa]

I am designing a cheapo hot tub, and want thoughts on potential problems I might have. It need it to be powerful, as I am going to hike to it and do not want to wait for hours for it to heat up. I want to use a 4 gallon propane tank and be able to really cook it up at first, then turn it down.

I plan on using a rubbermaid 150 gallon farm bucket, as it appears to be comfortable. Drill a 3 inch hole low on the sidewall and insert a 3 inch copper pipe that makes a "u" shaped bend before rising up and out of the tub. I would then fill with water and insert a propane torch (on the low end) set it on low and wait until the chimney creates a draw strong enough to support a higher temp.

Thats it. What do you think?

other points....

1) I will make a good seal at the hole.

2) The torch flame will begin six inches inside the tub, away from the plastic wall enough to not melt the wall with the copper pipe.

3) yes the copper will be spendy (any other materials)

Thanks!

Tor

[Mark Monson]

I would then fill with water and insert a propane torch

It sounds like it will work, provided you can achieve a good copper/plastic seal. You'll need a bulkhead fitting or such. What's your plan for this? Conventional water heaters have flues of less expensive steel, but for your purpose I think copper is the best choice.

How will you fill and drain the tub?

MM

[Runningwater]

Do you live in West Virginia?

[<JP]

Check Bill L's home made hot tub. Its in his folder in Yahoo's Vietnam NG. He is from Tennessee.

[torlissa]

I plan on draining it with a pail, but a plug in a hole would be good too.

tor

Thanks for the comments, I will have to check out all my seal choices.

[torlissa]

I am up here in Washington State. Nice out this time of the year, but a bit of a soak would be wonderful in a month or two.

Could you pass on a link to Bill L's hot tub, as I do not have enough info to find it on my own.

Tor

[Jeff Wisnia]

How BIG a propane torch flame are you envisioning using Tor?

I've got a funny feeling that geting the number of BTUs needed to raise

150 gallons of water from ambient to whatever temperature you like to stew yourself from a propane torch may take more time than you expect, even if you can extract most of the heat from the flame.

You'll have 17 pounds of propane in a four gallon tank.

Let's see:

It takes one BTU to heat one pound of water one degree Fahrenheit.

150 gallons of water weighs 1251 pounds.

To increase the temperature of that much water by 50 degrees Farenheit will take 62,550 BTUs

Propane contains 21,548 BTUs per pound, so it will take the heat from almost three pounds of propane to raise that much water by 50 degrees Farenheit.

That's of course if the transfer of heat from the flame to the water is

100% efficient, and there's no heat lost through the walls and bottom of the tub, and off the surface too, none of which will be the case.

So, if you know how fast the torch you are thinking of using will consume three pounds of propane you can get some sort of idea of how long it will take to heat the water in your hot tub.

You didn't mention insulating the sides and bottom of the tank, but you better consider doing that, or prepare to spend a lot more for propane.

Just my .02,

Jeff

[torlissa]

Jeff,

Thanks so much for the brain work. Makes this internet thingy seem awfully cool. Do you have any thoughts on problems I may have with a torch running within a copper pipe? I am going to shove the torch deep enough that the beginning of the flame will be away from the plastic wall. The water heat sink should be enough to keep that end cool, but the exhaust end may be quite hot if I turn it up so much the the flame burns within the entire submerged pipe, and even burns as it exits the wall. I guess I will need to get some pipe and test the lengh of the flame within at the level I want to run it at. I was thinking of around 6 feet of 3 inch copper submerged.

My other, less shody (but not much) way of doing this is to purchase a heating coil by the company Zodi.

One product they offer is a stove top water heater (coil on demand) that is rated for a 35,000 btu propane stove. It comes with a battery operated pump and hoses to run a shower. I just can't see the little pump doing it. The heat loss would seem to exceed a submerged element like my design, I could be wrong though.

They sell them in many BTU's I was thinking of running one at 30,000 -

40,000 btu's at first, then kicking it way down.

I am dreaming of around three hours, that seems to be within your calculations, if I can keep the loss down. The thick plastic is pretty non-conductive and a floating bubble blanket would help too. I mainly want to rig up something as powerful as I can get with a four gallon tank. I can always fill the tub with less water, it will probably only hold 100 with two folks jammed in it anyway.

[Jeff Wisnia]

I've pretty much shot my wad already on what advice I can give you without actually designing and trying stuff to see which direction to tweak your design to get what you need.

I am going to shove the torch deep

Frankly, I wouldn't want to even guess at what is going to happen to the performance of a torch designed to be operated in free air when you stuff it inside a length of pipe, but I'd bet dollars to donuts that the performance won't be optimized.

Looks far too wimpy to me.

I think that If I had to do a "one off" like what you're trying to achieve I'd look for a galvanized metal tub with a strong enough bottom to contain the water when the tub is supported near its edges, stand it on a bunch of cement blocks and place a suitable sized propane burner (or burners) under it. You might be able to locate one support in the center too, with a couple of burners on either side of it. What's wrong with that? And, if you run out of propane before your bodily desires are satisfied you could always burn some hand cut wood under it.

Or, contract the whole freakin' design job out to a group of cannibals.

Good luck,

Jeff

[<JP]

I'll give a look see...its been awaile since I was in that NG.

[torlissa]

I haven't thought of a tin tub, all I have heard of is cast iron, and I can't get one of them to the location, but a tin one....

Thanks for the advise!

Tor. I'll send picts if I get it going.

[Mark Monson]

I've been pondering the "Cheapo Hot Tub" concept on and off for a few years now.

Have you seen the galvanized horse troughs at Farm and Fleet?

MM

[torlissa]

Yes, I just went to look at some. I saw the rubbermaid 100 gallon and

300 gallon. But they also had a slightly more expensive galvenized tin trough that looked swell. It even had a welded "gunwale" rim that looked ok for sitting on. 100 gallons, 89 bucks. That and a $20 blowtorch burning at a couple hundred thousand BTUs and I think I will have a great travelling tub.

tor

[Blackbeard]

Alright...so you want a cheapo hot tub. I assume you want the hottub to be portable (on a trailer) so here's how you can do it.

Build a surround out of lumber (I would suggest you build it directly on the trailer and bolt it to the trailer). Basically build a shower stall right onto the trailer (except yours will have short sidewalls and bracing to accommodate for the water).

Sheet off your surround with 3/4 plywood.

Use rebar bracing through the studs and especially at the corners for additional support bracing.

Cover the inside of the box with chicken wire.

create smooth curves in the wire to produce the visual that you are going for. (you don't want hard uncomfortable seating do ya)

Drill holes and install your plumbing.

Take your trailer to a concrete company and have them spray the inside (the chicken wire) with gunite.

manually smooth the gunite to a smooth finish.

Now for heat...Use a full coil of 3/4 coppe roll (60-feet). Wrap the soft copper around a section of 24" concrete pipe. When you remove the coil from the concrete pipe, you should have a coil of copper with a

2-foot opening down the center.

Grab your torch and put solder between the coils of 3/4 pipe (we don't want that coil collapsing - we want a 2-foot diameter tube of coiled copper.

Now mount a burner (250,000 btu) in the center of that coil. The burner will heat up the coils which will heat up the water. You will need a small circulator pump.

Now to put it all together. Fill your hottub with water. Turn the circulator pump on (to prime your coils)

Light your burner

The burner will heat the water FAST

enjoy

(note: this burner will heat the water VERY hot. Use an aquastat to control temperature. This type of coil can get your water temperatures up to almost 300-degrees (straight steam). Make sure you have some safety devices installed. 300-degrees water will kill you.

[Runningwater]

wow, this is an awful lot of work, time and effort for sumthing you can go buy one already done used condition for around 12-1500 bucks. You'll probably have more than that in materials.

[Blackbeard]

Well he wanted CHEAP...

Actually, the cheapest way is to get >

[Ned Flanders]

Alright I think we have it.

Tin tub Attach propane grills to bottom of tub. (4) Hook em all up to one tank You could put an ignitor in there and your own gas valve. You need some screen thingy for bottom so you dont burn yours.

[Blackbeard]

So your idea is to heat the water directly with no thermostat and no safety whatsoever....

Hmmm.

Nobody here is going to rubber-stamp that idea. Your idea could be fatal.

But what the hell - go for it.

[Ned Flanders]

yeah not like that other guys idea