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Author Topic: On Demand Hot Water  (Read 3768 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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Busted Knuckle
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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.

craig
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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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Christyhicks
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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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