Diesel heater thru hull for exhaust.

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Cigatoo

Cigatoo

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Joined
Sep 9, 2016
Messages
1,905
Location
Narragansett Bay
Vessel Name
Cigatoo
Vessel Make
Grand Banks 36 Classic #715
36 Grand Banks
I have an unused 3/4 inch thru hull about 2 inches above the water line. (Was previously used for refrigeration water outlet). I would like to install a diesel heater. The heater will be mounted about 2 feet above the water line / un-used thru hull. Was wondering if I could use the same thru hull hole for the diesel heater exhaust. Obviously new exhaust thru hull and pipe will be (good quality) stainless. Was thinking of welding a piece of solid stainless pipe onto the new exhaust thru hull with upward slope for a few inches / feet in place of the flexible stainless exhaust pipe.
Pros
Will provide for a good downhill slope to drain condensation.
No additional holes in the hull. (Hull is solid glass)
Cons
Very close to waterline.
Forcing hot exhaust down could be a problem?

Thoughts appreciated
 
Last edited:
I would think that the outlet being deeply submerged in a big wave would cause a back pressure issue on the exhaust that would make the heater run bad, or possibly be dangerous? If you have engine heat when under way it might be fine, but still seems sketchy to me. I would do a fiberglass repair on the existing hole to make it disappear, and put the exhaust in an optimal location.
 
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The installation instructions I have seen for diesel heaters would prohibit such an installation. It would not take much or a roll or a wake slap to drive water up two feet above the WL.
 
My first concern would be that a 3/4" thru hull is likely way too narrow - so highly recommend checking the heater specs for minimum diameter of exhaust hose (e.g. the Webasto 20xx DBW series heaters require a min diameter ranging from 1.5" to 3.2"). While I haven't measured it, my thru hull appears to be a 3".

I echo Snapdragon's concern w.r.t. the location being too close to the waterline. Mine exhaust port is about 2.5 - 3' above the waterline.
 
What a diesel heater exhaust looks like. It has a space around the exhaust pipe to limit heat transferred to the hull. On ebay.com Straight or angled about $20
Heater Exhaust Thru Hull.jpg
 
Bad location. Normally mounted much higher , or on the stern. If anything restricts the flow it will shut down. The heater exhaust intake has specific requirements. Refer to the manual.
 
We had our Hurricane heater professionally installed to replace the original Hurricane heater and the installer was concerned about the height of the original exhaust outlet which is about 18 inches above the water line due to wave exposure.
 
Coincidental timing. I’m in the process of installing a diesel heater today.
Instructions call for exhaust outlet to be a minimum of 300mm above water line and the hole drilled for the above pictures fitting was 1.5” hole saw.
These exhausts throw a lot of heat so you need the correct fitting.
 
Agree the existing hole is too low and that the through-hull needs to be special purpose for a heater and insulated, per Lepke above. Also be sure to put a loop in the exhaust run so water can't easily get to the heater's boiler.
 
I mounted mine up high just below the gunwale. Four year now and no problems and the diesel heater is remarkable. Such nice dry warm heat verses a propane heater.
 
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