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Author Topic: On Demand Hot Water  (Read 3871 times)
captain ron
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« on: September 24, 2007, 06:56:35 PM »

I just purchased a Bosch on demand water heater. It is N/G but I'm converting it to propane. It is a home model so I know  it's overkill for the bus. I'm hoping to use it for hot water, engine heater and at least some bus heat. It's pretty big and needs to be vented so I plan on putting it in my engine compartment curb side and venting it out the side. Any advice, comments or nay sayers?
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« Reply #1 on: September 24, 2007, 07:35:15 PM »

nay!





But then I don't know a darn thing about 'em either! LOL! Grin  BK  Grin
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« Reply #2 on: September 24, 2007, 07:52:22 PM »

Should work for your hot water but how are you going to heat your engine coolent without some kind of heat exchanger. Be interesting how much propane it will use.
Ron
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captain ron
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« Reply #3 on: September 24, 2007, 08:05:52 PM »

I plan on putting in a heat exchanger. It is the Bosch Aquastar 125B. It calls for a power vent if ducting horizontal but I am  venting it so close to the unit I don't think I'll need it besides they want more for the power vent than I paid for the unit.
NIB $300.00
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« Reply #4 on: September 24, 2007, 08:23:45 PM »

Captain Ron,

That is an incredible price!  What a find.  The on demand actually uses less propane per unit of heated water than a conventional heater.  You are SOL on the engine preheat scheme.  You could plumb with a return to your fresh water tank and heat that water and the wet bay to prevent freezing.  I intend to stack my gray and black over the fresh and heat the fresh to a snuggly 45 degrees and keep everything liquid in sub zero temps.

John
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« Reply #5 on: September 24, 2007, 09:10:22 PM »

Most instant water heaters require a drop in output line pressure to turn them on. Probably not going to be able to use a heat exchanger to preheat the engine unless you are cycling water through the unit continuously.

Also, if you put it in the engine compartment, how are you going to keep the lines to and from it from freezing when not in use. Also, the heater itself might be at risk of freezing when not being used.

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captain ron
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« Reply #6 on: September 24, 2007, 09:17:21 PM »

Most instant water heaters require a drop in output line pressure to turn them on. Probably not going to be able to use a heat exchanger to preheat the engine unless you are cycling water through the unit continuously.
I'm sure it can be figured out  Huh

Also, if you put it in the engine compartment, how are you going to keep the lines to and from it from freezing when not in use. Also, the heater itself might be at risk of freezing when not being used.

craig

Water doesn't freeze at 85 deg.  Grin
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« Reply #7 on: September 25, 2007, 04:34:16 AM »

Um, I thought  you had to buy those units as either NG or LP.  I didn't think they even sold conversion kits for them, because normally, you have to also use a combustion analyzer to even replace a gas valve. . .at least, it's that way on their higher-end units. 

We do a lot with tankless water heaters, but I normally don't deal with the 125b units. . . are you going to have enough flow to activate the heater?  Make sure you seal the compartment really well, because, normally, a natural draft appliance needs "draw" on the flue to help it vent. . . so usually they require a minimum height of flue, I think it used to be 6' on the 125, but not sure if they've changed it or not.  You'll need to seal the compartment extremely well, and then bring your combustion air in from outside and make sure that compartment stays well ventilated.  Also, watch your clearance requirements. . .it used to be about a foot above and below the 125, which meant you needed about a 4-5' tall space for it.

Normally, on that lower end of the tankless units, you also have to have good water pressure and flow. .. I think the minimum pressure was 30 lbs, and our experience was that if you don't have over 40 lbs, you just have a hard time getting the unit to fire. 

I'll tell you what I'm thinking of doing. . . I bought a little non-vented tankless off of Ebay, and stuck it in my office to serve the bathroom and kitchen area in our office.  Much to our surprise, testing the air with a few feet of the unit showed no CO present, and the only time we could get even a trace of a reading was by testing the air right at the top of the unit.  It's been in for about a year and a half, and has never set off the CO detector, which is placed about 8' from the unit. It is a tiny unit, designed for a single appliance, but since our office is probably 2500-3000 feet from our well, we run fairly low flow up there anyway.  The unit has no problem keeping up with any faucet, including the bathtub when the grandbaby gets a bath, so I think it would work pretty well on an RV water system.  I'll do some searching and see if there are any more for sale.

Let us know how your situation develops and be sure to tell us all the details that you can, as we are a few steps behind you and would be GLAD to learn from anyone's successes  Grin and mistakes, ha ha Cheesy.  Christy Hicks
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« Reply #8 on: September 25, 2007, 06:22:15 AM »

Hey Ron.   I just purchased your old 4905.   Anything I need to know.   Where did it come from?   larrydbaker@netscape.net
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captain ron
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« Reply #9 on: September 25, 2007, 06:32:28 AM »

Hey Ron.   I just purchased your old 4905.   Anything I need to know.   Where did it come from?   larrydbaker@netscape.net

Too late now  Grin








Just kidding, it was a good ole bus and Glen made it even better. I used to get between 7.5 and 9.5 MPG
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Nick Badame Refrig/ACC
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« Reply #10 on: September 25, 2007, 03:06:47 PM »

Hi Ron,

I think you should reconcider the power venter...

Reason, the temps comming out from the flu will be greater then 400 deg's that close to the unit.  Even high temp silicone will burn that hot.

second, a local contractor here just paid a big bill to his customer for burning half his house down by not installing an external power venter on a

heater replacement that was a side wall vented set-up. We were the company that corrected the install after the damage was done.

Here is a PDF on guidelines for side wall venting.

http://www.tjernlund.com/8500594.pdf

I will find some more litature for you tonight.

Nick-

« Last Edit: September 25, 2007, 03:11:48 PM by Nick Badame Refrig. Co. » Logged

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captain ron
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« Reply #11 on: September 25, 2007, 06:06:47 PM »

Most instant water heaters require a drop in output line pressure to turn them on. Probably not going to be able to use a heat exchanger to preheat the engine unless you are cycling water through the unit continuously.


Been thinking about that and I could put in a return to my fresh water tank with a valve on it and then the following question would be partially answered.

Also, if you put it in the engine compartment, how are you going to keep the lines to and from it from freezing when not in use. Also, the heater itself might be at risk of freezing when not being used.

craig


If I can actually use it to heat my bus or my WVO then that won't be an issue. But I'll try to stay in above freezing temps, at least that's my goal.
« Last Edit: September 25, 2007, 06:08:27 PM by captain ron » Logged
Nick Badame Refrig/ACC
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« Reply #12 on: September 25, 2007, 06:31:21 PM »

Hi Ron,

The vent kit for your Bosch is the AQ1 as they list it in your installation instructions. 
http://www.boschhotwater.com/Portals/7/TechManuals/AQ1manual_1003.pdf

It is the same exact kit that is manufactured for them by Tjernlund- #GPAK-JT Either kit would work for your heater.

Tjurnlund supplies most all manufactors for venting needs in the US.

I have seen the GPAK-JT selling for a little over 200. if you need me to find it for you, I will.

Please don't ignore this venter, it's way too critical.

Nick-
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« Reply #13 on: September 25, 2007, 06:33:32 PM »

I did just what you are talking about, I can heat my coach, pre heat the eng. and my domestic hot water. I have a precision temp lp unite. Or I can do all the same from the eng while traveling.
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captain ron
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« Reply #14 on: September 25, 2007, 06:57:38 PM »

I did just what you are talking about, I can heat my coach, pre heat the eng. and my domestic hot water. I have a precision temp lp unite. Or I can do all the same from the eng while traveling.

You got some pictures and drawings of your system you want to share? Some info on how you made it work.

Nick, I was looking through the manual and parts book. not real sure I can change this to LP that easily or inexpensively. The main burner, pilot injector,throttle disk and gas valve all have different part #'s, does this mean all of these parts need replaced or just some. I am not married to this unit as the guy can use it at home and I don't have to take it.
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« Reply #15 on: September 25, 2007, 07:04:58 PM »

Yes Ron,

Injector [orfice], gas valve, and throttle disc all need to be replaced as well as doing a check on the LP pressure when done

to insure that you don't exceed 11 in of water collum.

My 12 gal electric h2o heater recovers in 40 min's and will stay hot for 2 days...... Never had a problem of no hot water even when my 3 kids are along..

When the day comes that it brakes, it will only take $15 dollars to repair it. [2500watt element]

Nick-
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captain ron
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« Reply #16 on: September 25, 2007, 07:19:16 PM »

I have a 2 gal. electric I will keep as a backup but have always wanted a propane on demand system. I have a huge propane tank mounted that is not being used. I may have jumped the gun a bit on this one but you know how I am, I get a thought about making something work and I jump in head first. How much do you think I'll have in converting to LP?
It only needs 1/2 to 2 gal per min. water flow to operate.
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« Reply #17 on: September 25, 2007, 07:46:37 PM »

Ron, be sure to allow for the combustion air and flue gas the on-demand water heater needs. Their needs are generally greater than for a regular water heater.

For what it's worth.

Tom Caffrey
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« Reply #18 on: September 25, 2007, 08:02:32 PM »

I think that counting on 1/2 gallon per minute flow rate to activate and run this unit is, well, let's just say that they "claim" it, but the reality is that very low flow is a PITA for tankless water heaters.  We find that the more flow you have, the better they work.  The problem is never "not enough hot water", but rather it is a problem with the unit shutting down on overtemp.

I'm serious. . .take a look at the Excel water heaters on Ebay. . .see if they have any LP ones.  That little unit I've got in my office is reminiscent of the old Paloma's you would occasionally see in RVs, many years ago. 

I don't sell them, and have no interest in them, but we've sure worked on a lot of tankless units and this little buger seems like it would be perfect for the bus converter.  Christy Hicks
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« Reply #19 on: September 27, 2007, 08:18:41 AM »

Hi Nick,
When I needed some high temperature sealant recently, I went to the automotive section of the hardware store and got some Permatex Sensor-Safe Blue RTV Silicone Gasket Maker, NO. 6BR. It is rated for 500 degrees, that was high enough for my need. There is also Permatex Ultra Copper Maximum Temperature RTV Silicone Gasket Maker, NO. 101BR, rated for 700 degrees. See www.permatex.com. In the event that you ever need a high temperature sealant, they are available.
Thanks, Sam 4106
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« Reply #20 on: September 27, 2007, 08:15:27 PM »

I did just what you are talking about, I can heat my coach, pre heat the eng. and my domestic hot water. I have a precision temp lp unite. Or I can do all the same from the eng while traveling.
Inquiring minds want to know how you did it! What did you do? And please by all means please post pics and details! Ron has cut up everythink in th shop waiting to here how this was done, and I'm afraid the shop is next! FWIW Grin  BK  Grin
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« Reply #21 on: September 27, 2007, 09:12:40 PM »

Ron,

I have one of those that I got a couple of years ago...

They need 2 to 3 gallons per minute to activate and keep running...

They also require a high flow gas regulator rated for 100,000 btu.. Or simply to say
enough flow to cause a 30 lb propane tank to frost up in about 10 minutes.

The conversion process is very very involved since there are rows of tiny nozzles
in the injector bank. each must either be replaced or resized for less flow.

LP Gas has a higher BTU content than Natural Gas.. So they use larger orifice/nozzles for NG.
( If you don't change them you will burn black soot out the stack...)

The fuel regulator valve is also slightly different, it has a different part number in the manual.

You may find that space, fuel and venting requirements will haunt you.. The exhaust temps can peel paint off if the heat blows back onto the surface of the bus.

There is a specific demand LP water heater made for RV's.. It's just expensive.. It also totally vents everything outside.

The Bosch will get everything in the bay very hot because it wasn't designed for confined spaces and those open flames in the burner area may not be the wisest to have. They also won't work if there is a breeze.. The burners blow out easily....BOOOM....

Dave... Undecided
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captain ron
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« Reply #22 on: September 28, 2007, 09:49:00 AM »

Thanks guys for crushing my dreams, Back to the drawing board. Huh
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« Reply #23 on: September 28, 2007, 10:18:10 AM »

Ron,

I have one of those that I got a couple of years ago...

They need 2 to 3 gallons per minute to activate and keep running...

They also require a high flow gas regulator rated for 100,000 btu.. Or simply to say
enough flow to cause a 30 lb propane tank to frost up in about 10 minutes.

The conversion process is very very involved since there are rows of tiny nozzles
in the injector bank. each must either be replaced or resized for less flow.

LP Gas has a higher BTU content than Natural Gas.. So they use larger orifice/nozzles for NG.
( If you don't change them you will burn black soot out the stack...)

The fuel regulator valve is also slightly different, it has a different part number in the manual.

You may find that space, fuel and venting requirements will haunt you.. The exhaust temps can peel paint off if the heat blows back onto the surface of the bus.

There is a specific demand LP water heater made for RV's.. It's just expensive.. It also totally vents everything outside.

The Bosch will get everything in the bay very hot because it wasn't designed for confined spaces and those open flames in the burner area may not be the wisest to have. They also won't work if there is a breeze.. The burners blow out easily....BOOOM....

Dave... Undecided

With all the options, it's $1000 and worth every penny!

Jay
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« Reply #24 on: September 28, 2007, 10:28:01 AM »

Ron,

I have a SW12DE that is a 12 gallon, propane or electric 110vac water heater.

http://www.folandsales.com/catalog.asp?prodid=489489&showprevnext=1

I bought this as an almost new takeout from a wrecked RV for 325.00/579.00 new.

I have only used the 110 side and it works great, has an electric start for the propane.

I am switching to an electric only as it fits my usage and setup better.

If you would be interested in buying it(275.00), let me know and I will bring it to the rally at the cove.

Cliff



 

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captain ron
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« Reply #25 on: September 30, 2007, 08:33:42 PM »

Cliff, the web sight won't load. Can you send pictures and specs please?
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« Reply #26 on: October 01, 2007, 04:48:16 AM »

Ron, it loads on my puter, come on over and you can check it out.  Cat
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« Reply #27 on: October 01, 2007, 06:45:21 PM »

Ron, if you have enough propane capacity, you may want to consider this unit.  http://precisiontemp.com/pt_rvmd_twintemp2.html The TwinTemp2.
Like a Webasto or AquaHot, it will meet your hot water, and hydronic needs using fuel or electricty, but uses propane instead of diesel.
My propane is $1.85/gal delivered, has been within 10 cents of that price for over 3 years, and I feel is quite the bargain.

Jay
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captain ron
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« Reply #28 on: October 01, 2007, 10:18:29 PM »

At over $4,000.00 I don't think so  Huh
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« Reply #29 on: October 01, 2007, 10:38:09 PM »

At over $4,000.00 I don't think so  Huh

Seems like the JR is around half that amount...or was when I first asked about it.

Jay
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captain ron
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« Reply #30 on: October 01, 2007, 10:41:21 PM »

That is still more than I want to or would spend. I like trying to build my own. Thats why we do these things anyhow, Right?
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« Reply #31 on: October 02, 2007, 08:51:15 PM »

I have a Bosch LP installed at the driver rear underneath the radiator vented out on the outside of the radiator.  Of my MCI seven right now I'm just using it for hot water.  And it is working great.  I believe it is a 125.  It is a 3.7 gpm I will have to dig out the pictures.  It was a tight squeeze.  As for the water lines freezing.  I'm staying in the South, Houston and Tucson.

But I didn't have a rope light underneath it for winter temperatures of about 32° and had no problem.  I would recommend a good heat tape or colder areas.  If you get calculations on how to use for heat in the living area.  Please keep me informed.

I know this unit uses a Hydro switch.  I believe it is a turban, rotating inside the tube as water passes by and generates a spark.  This one uses no electricity, from an outside source.

Good luck, Ron
John
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