OK to use home 50 gallon propane water heater for soaking tub?

[Kevin Warnock]

Hello,

I won't be ready to install the bathroom for a while, but I'm busy thinking about what to do already. I plan to use a full size home bathtub. I want to be able to soak in the tub with the water filled to the top, yet not be tied to campgrounds with hookups. So I have something different planned, and would like your comments, please.

I plan to have two water sources for this tub. The first would be a wall mounted control just like you would find in a shower stall. The water would come out of the wall at about the height of a standing person. This water would be heated by an on demand water heater. The water would come from the fresh water tank that also will serve the kitchen, vanity, toilet and washing machine.

The second faucet would be a normal tub faucet, with the controls mounted close the the lip of the tub, as is usual for tub installations. This water would come from a separate tank, and be recycled for additional soaks in the tub. It would also be treated like hot tub water is treated, so that it won't 'go bad.'

The process to use the soaking tub will be as follows:

1. Thirty minutes to one hour before, turn on 50 gallon residential propane water heater, to give it time to come up to soaking temp, about 110 F.
2. Take a normal soap shower standing in the tub to clean off before getting into my 'hot tub.'
3. Turn off the shower and let all the water drain.
4. Flip a Y ball valve to direct drain flow to the second water system. The Y valve will be under floor level by a few inches, and can be reached by opening the vanity cabinet and manipulating the valve handle, which will be at floor level since you can get a long shaft for such handles and leave the valve below the floor, but have the valve higher, inside the bus conversion. These Y valves are designed for the marine market and cost about $70.
5. Turn on lower bathtub faucet. This causes water to flow from the 50 gallon water heater noted in step 1 above into the tub. As the pressure in the water heater goes down, a hot water capable demand pump situated at the exit of the 80 gallon 'waste water' tank in the bay will turn on to keep the pressure up and keep the water flowing into the tub. There will be about 70 gallons of water in the waste tank and 50 in the water heater when the tub is empty. The tub holds 40 gallons when full to the overflow. Thus, there won't be a time when the pump can run dry.
6. Get in tub and enjoy a hot soak. When water cools, turn on the tub faucet again, and there should be hot water ready by then to warm up the tub. Water flows into the overflow opening of the tub and goes into the 'waste water' tank to find its way back to the water heater.
7. When done, open the drain and drain contents of tub into 'waste water' tank.
8. Flip Y valve in vanity back to 'shower' setting.
9. Turn off 50 gallon water heater until needed for next soak.

Sears sells a 50 gallon pilot light water heater than runs on propane for $410. The tub is cheap as I can use a standard Home Depot tub. I need two faucets, an extra pump and some extra plumbing. But overall, this doesn't seem too costly.

So, my questions are:

1. Will the chemicals used to treat the soaking tub water supply attack the water heater or plumbing in a way I need to worry about?
2. What hot water capable demand pump brand would you recommend? I see backwoodssolar.com has a 6.5 gallon per minute 24 volt model for $195.
3. What chemicals should I consider to treat the water? How long should I be able to keep one batch of water around? Since the water will be hot much less than a real hot tub, that might change the number.

I have room for the water heater, which stands vertically. Yes, I will brace it with amazing restraints, since it will be a heavy missile if it were to come forward in a crash.

The water heater will vent through the roof like a home model. This adds a 4th question:

4. How should I stop the heat or air conditioning loss of air from the living quarters from having a vent for the water heater inside the living part of the bus? If I put one of those spin 'doors' in the 3" vent pipe, and someone starts the water heater without opening the door, the exhaust will go into the bathroom. I will have a C0 and propane detector on board. What I need is an idea of how to make sure the door is open when the water heater is on. Any ideas? The water heater will be in a dedicated closet in the bathroom. I could make this door sealed with weather stripping, and cut vent holes through the floor so that in effect that closet is part of the bay and not the living quarters, air wise. Then I can leave the flu vent open all the time. However, if I do this, the water will be much colder and take much longer to heat up, so I'd prefer a different solution. I see some home water heaters have powered fan vents that turn on when needed. Would such a heater shut the vent when the heater is off? If so, that may be the easiest way to go.

Thanks for your comments.

Kevin

[Ednj]

Get yourself a flat plate heat exchanger and a diesel fired Proheat, and forget the rest .
You will never run out of hot water.

[DavidInWilmNC]

If you're going to treat it like a hot tub, I'd think you'd use hot tub chemicals and get hot tub life out of your water (a couple of months, but it should be treated and filtered regularly).  It sounds like you're talking about basically having a hot tub that drains back into a tank that, with some valves, you can use as a shower.  I'd think you could also use an ozonator to help keep the water good and reduce the need for chemicals. 

David

[Dallas]

Kevin,

I deleted your recurring posts.

Woo-Haaaaa!

The board is up and life is good!

Dallas

[H3Jim]

For the hot water heater you could make the fresh air supply from either a bay or below floor lever somewhere.  That way its fool proof, you never have to open or close a vent, and neither will it take air from yoru living quarters.  it would be like a pipe with openings on the bottom and top, and nothing inbetween.  YOu might have to get a little creative about how you box in the intake, but it seems doable.

Alterantively, Sean Welsh I thought was a dealer for some inflatable hot tubs.  he uses his diesel fired hot water heater and a heat exchanger to heat his water.  With his set up however you do need access to water each time.  I think he also has a pump and can pump water from a stream if he's parked close enough.

[TrevorH]

One thing to consider aswell will be the fact that your hot tube is inside of a small area.  Keep this in mind when selecting the proper chemicals.  You should also pay close attention to where the steam is going to go.  You would not want to rot out your ceiling and walls.  For your home water heater, how about cutting a circular hole in the floor and having the lower area where the burner is located in a storage bay under the bus and the top half up in living quarters.  This would provide for fresh non living space air for your burner and also a major support structure for the tank.  Just an idea...

[NewbeeMC9]

Why not insulate the holding tank and run heating tubing/coils through or under it.  even a waterbed heater underit possibly,  your bath water will only need to be 108? or so, then use a proheat or such that heats your,  you will also have other choices for heat supply the too


I've heard good things about the salt ones
no clorine to buy
self regulating and last a long time, salt is cheap, like $5 for 40 lbs

downside is it needs more electricity, don't know how much.

if you run the generator for the purifier before your your bath, you could use the waste heat for the recyclebath water.  also if you run the genny during you could use a jacuzzi tub and recycle.

you may want to use a changeble filter to help the recycle water

just a thought, HTH,  Let us know how you work it out,  this is interesting,  pics

[Lin]

You probably want to speak to someone very knowledgeable on spas to get the chemical thing right.  We have one and use minerals, ozone, and some bromine to keep the water up.  It is also required to shock it with an oxidizer weekly.  Filtering is another issue.  The water should be run through filters for several hours a day.  Ours is a small one, but we still need two two hour filterings a day.  There are all sorts of health risks if the water is not treated right.  If you are only talking about a bathtub, using fresh water may be the easiest and safest way to go.  You don't want to be taking your daily soak in what is essentially gray water.

[Melbo]

Just a suggestion but you should consider a mobile home water heater -- they are a sealed combustion water heater and the combustion air goes in the bottom center of the heater and the exhaust vents out the top ( not using a draft hood setup ) and none will bleed or vent into the area where the heater is located.

You have to be sure that you get a Mobile home sealed combustion water heater because a residential sealed combustion water heater will get its make up air from the top and send it down the outside of the heater to the combustion chamber but a Mobile home heater draws it from the bottom. The residential heater will require a much larger opening at the exhaust vent than the mobile home heater will also the residential water heater is much larger in diameter than the mobile home heater.

I'm not sure how the chemicals will affect the heater or the lining. I know that chlorine will etch glass and the water heaters use glass linings. You might consider changing the water anytime you get a chance and other wise keep it treated so it doesn't get funky. Also because you are experimenting here you might want to be sure and put the heater in a pan with a drain so if it does go (with certain water conditions I've seen water heaters crap out in less than 4 years and they start as small leaks and deteriorate rapidly) the water will drain out of the bus and not ruin your living area.

Of course this whole diatribe is just the opinion of a simple mind. Good luck with whatever you finally decide to do.

Melbo