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Author Topic: Pex & hot water question  (Read 3582 times)
rayshound
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« on: June 22, 2007, 06:50:20 PM »

I am installing my webasto plumbing now. I'm using pex for the baseboard radiators & for & engine warmer. I had put a red dot front dash a/c & heat out of an airport shuttle bus in my mci.  My question is do I hook the dash heat to the webasto or to the engine. I had removed the old lines for bus heat. Could I use pex to hook dash heat to engine? Pex rated at 180 degrees f @ 80 psi.  Engine psi <15 psi.  I appreciate some thoughts on the idea.  Thanks Ray
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Jerry Liebler
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« Reply #1 on: June 22, 2007, 06:58:47 PM »

If you are using pex for a hot water heating system it's strongly advised that you use the type that has an oxygen barrier in it.  The reason for the barrier is to reduce corosion of iron and steel portions of the hot water heating system, this is not a concern with domestic water systems.  I kept the defroster on the engine coolant system thinking I'll need it many times when I don't need the Webasto and don't want to wait for the Webasto's coolant to heat up.
Regards
Jerry 4107 1120
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Nick Badame Refrig/ACC
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« Reply #2 on: June 22, 2007, 08:12:31 PM »

Hi Ray,  How are you?

Jerry has a point about the OB Pex. Question, if you are parked, will you be able to run the dash fan inconjunction with the Wabasto without draining your start batts?

If thats a concern, then I would keep the dash system seprate and let the engine heat it.

Good Luck
Nick-
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rayshound
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« Reply #3 on: June 22, 2007, 09:05:13 PM »

Thanks that makes sense. Would using pex from engine to dash heat be o.k. or to hot?  Thanks Ray
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Don4107
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« Reply #4 on: June 23, 2007, 12:02:21 AM »

I have not finalized the plan yet but I want dash heat from both the engine and Webasto.  Why, all that glass.  It lets in a lot of heat when hot out and looses a lot of heat when it's cold.  It may be more complicated than useful, but I have been working on the design anyway.
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Don 4107 Eastern Washington
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« Reply #5 on: June 23, 2007, 01:51:54 AM »

Whatever you choose…make sure your heated water supply flow is great enough to get the BTU you need in the worse condition. At least 1” ID hose or pipe or tubing from engine and then reduce to fit exchanger unit..

Suggest to always connect to engine as well diesel heater in series with return line from dash heater to inlet and 2 way valve to by-pass front dash exchanger. Its primary purpose is to heat engine and/or interiors. If want to heat potable water…get a marine heat exchanger build into electric water heater. Another word a marine heater with 2 inlets & 2 outlets.

FWIW

Sojourn for Christ, Jerry
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Nick Badame Refrig/ACC
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« Reply #6 on: June 23, 2007, 03:48:58 AM »

Thanks that makes sense. Would using pex from engine to dash heat be o.k. or to hot?  Thanks Ray

Ray,

One thing you would have to concider, if you were to have an overheating problem, you can get as hot as 210 deg's before your engine
would cut out, and then at that point it could go another 10 deg's up before cooling down.
Heat PEX would be a better choice in my book. My Oxygen barrier PEX is rated at 250 deg's.
Nick-
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Gary '79 5C
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« Reply #7 on: June 23, 2007, 04:01:30 AM »

I would like to re-ask the point Sojourner made about installing the Webasto piping to route hot water thru the cabin heaters, and the engine block,( hot water heat exchanger).
Are there any problems/ downsides to doing this. I see one obvious problem and that is there is many additional hoses & connections any of which could leak and shut down the engine with loss of coolant.
Other than that I am fine with it, This set up has served me well. I do see that Dick Wright sells ( and reccomends) a SS heat exchanger to "separate" the engine coolant system, but still share the heat.
This system is great upon waking up in freezing temps outside, I and my engine are warm and cozy.

Enjoy your weekend folks,
Gary
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edroelle
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« Reply #8 on: June 23, 2007, 05:45:47 AM »

Jerry is right.  Use large piping.

Heat exchangers between the Webasto and the bus engine are usually recommended.  I did not do it that way.  I did not see a problem in eliminating this component other than the failure mode - if a line ruptures and you lose your coolant.

I used the original bus lines and tied-in my Webasto in the front.  I valved the lines so that I could bypass the engine, or the living area heat exchangers.  Thus, the Webasto, or the bus engine, could heat the living area and/or the heat exhanger in the hot water heater.  This also allowed for the Webasto to preheat the engine.

When I shut-off the valve to the engine, I just shut the one valve at the right rear, to prevent flow.   (The valve in the center of the bus engine compartment is also hard to access.)  By leaving one of the two valves open, allows for coolant expansion such that an additional Webasto coolant tank was not necessary.

Design your system on paper so that the coolant flow makes sense.

Ed Roelle
Flint, MI
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rayshound
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« Reply #9 on: June 23, 2007, 08:04:45 AM »

Thanks everyone great info, now let me really push the envelope with this question. If I use say the 1" hot pex to run from the engine to the dash heater in my mci-8 the old floor a/c duct I had removed and added unistrut and had run several conduits from front to rear. The duct isn't covered yet & plenty of room but when I lay down the plywood access is gone. could I use 1&1/4" or 1&1/2" conduit with the long radius bends to run the 1" pex in and use as a "chase" ?  That way any future problems I could pull the pex out to replace. Would the conduit get to hot? Do you think it would sweat? Would it be better to run the pex in plastic water pipe. I would not have the long radius 90 degrees. Thanks Ray
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Nick Badame Refrig/ACC
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« Reply #10 on: June 23, 2007, 08:38:58 AM »

Ray,

When you said you removed all the orrigianal heat lines in your first post, I guess you don't still have them?

Nick-
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edroelle
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« Reply #11 on: June 23, 2007, 09:52:30 AM »

Conduit is OK.  I used inexpensive black flexible polyethylene (Home Depot water pipe) as conduit in that tunnel area - front to back, and to systems bay.

Ed Roelle
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rayshound
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« Reply #12 on: June 23, 2007, 10:59:41 AM »

Nick, yes I cut all the a/c & heat lines. Over kill I guess but I really cleaned out the chase. I removed floor, removed plywood in a/c duct floor & steam cleaned the tubings, and removed all the above mentioned. I had to cut into sections to get out. I por15 everything, used pour foam on the 4 wheel well areas and am presently running new a/c & heat lines in the a/c tray using two layers of unistrut & several plastic conduits from engine area to the nose wheel well. I know the lines could have been reused but they were so very large & went to condenser bay & to dash. I would rather run new & correct size. I'm also rerunning new fuel lines (copper) with & extra just for a purge line to the fuel processor.
                                        Thanks again any more suggestions welcomed as now is the time soon the new floor will br liquid nails & screws.   Ray
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rayshound
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« Reply #13 on: June 23, 2007, 11:04:59 AM »

Ed. thanks for the reply. When you said you used the black plastic lines in the tunnel, did you run pex inside of it? Thats my thoughts on this is to use the grey plastic conduit with the long radius bend & run the hot pex inside of it to protect the pex and have a way to mount the pex & replace the pex at a later date if needed. I'm thinking 1&1/2" conduit to run the 1" hot pex in would have plenty of room. Thanks again. Ray
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edroelle
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« Reply #14 on: June 23, 2007, 06:13:43 PM »

I did not run Pex.  I ran the polyethylene for wiring and 4 aught battery cables and grounds. 

I see no reason that you could not do the same for Pex.

Ed Roelle
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