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Old 01-24-2018, 10:13 AM   #1
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City: New Bern, NC
Country: US
Vessel Name: Miss Deb
Vessel Model: Nordic Tug 37
Join Date: Sep 2014
Posts: 63
Diesel Heater Exhaust Hose Connections

Kind of a long story so be patient.

We are living aboard in New Bern, NC and have experienced record cold weather for this area. We have (2) reverse cycle units but were counting on the Webasto diesel heater as the water temps dropped. We've tested the Webasto heater several times since purchasing the boat 2.5 years ago but since we were not living aboard at the time we never had to rely on it.

Just before the worst of the cold was predicted to hit I decided to make sure that it functioned okay. The unit started but produced copious amounts of smoke and after running and producing heat for a few minutes it shut off. Repeated process, same result the second time.

Ultimately traced the problem to a blockage in the exhaust hose that put back pressure on the unit. As I removed the hose to clear the blockage (appeared to be a chunk of carbon or soot) I found that the hose clamps were rusted and almost fell off in my hands. Turns out that when this unit was installed all Webasto had were steel clamps. These are not standard band clamps because the hose is corrugated SS to withstand the exhaust temps and you need higher compression to crush the hose against the fittings. The hose is covered with an insulating sock and the clamps are not normally visible.

Moral of the story - if you have a diesel heater check your hose clamps periodically. There was real potential for the exhaust hose to come off the fitting and allow CO into the boat. Hopefully the multiple CO alarms would have caught the problem before it became dangerous but CO is not something to take chances with.


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Old 01-30-2018, 09:24 PM   #2
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I was inspired to check mine: a standard hose clamp was installed instead of the exhaust hose i'm off to the chandlery to find a suitable clamp...

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Old 02-07-2018, 06:56 AM   #3
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If the exhaust is insulated , be sure to check the temperature of the exhaust thru the hull fitting .

These heaters were designed as truck and bus heaters and steel does not catch fire easily , GRP does.
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Old 02-07-2018, 10:33 AM   #4
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City: New Bern, NC
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Vessel Name: Miss Deb
Vessel Model: Nordic Tug 37
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Posts: 63
FF - the thru-hull fitting is double walled so there is an air gap between the inner pipe that the exhaust gas actually flow through and the outer pipe that contacts the fiberglass.

Once everything is reinstalled and I will be sure to verify that is keeping temps at the hull under control.

On a related note - there is a small fuel filter in the diesel supply line to the heater. The filter is by Delavan and they offer repair kits with new filter elements rated for 25 and 90 micron. There was no indication in the Webasto literature on which rating I needed so I called them. They said 25 to 30 micron but that they only recommended their filter, using any other filter could lead to problems.

HOWEVER - their filter has a plastic body. Fortunately I was also talking to Sure Marine and they pointed out that the plastic body would not meet ABYC requirements for flame resistance. Like you, they commented that the Webasto Air Top units were originally designed for trucks and different standards apply. Sure sells the repair kit and I have it on the way from them.


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Old 02-07-2018, 12:18 PM   #5
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City: Port Townsend, WA
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Thank you for sharing your experience!
Port Townsend, WA
m/v Traveler - '79 Cheoy Lee 46 LRC
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