Installing a Diesel Heater on a Boat: Choosing a Through-Hull Exhaust Fitting
Comfort on board starts with a carefully planned installation.
A diesel heater installation on a boat needs more than a convenient place for the heater. The exhaust route, the hull outlet and the surrounding materials all need careful consideration.
This guide introduces two Sunster through-hull exhaust fitting options: the RP13 angled fitting and the RP12 straight fitting. Explore the differences, see installation illustrations and watch a boat-installation reference video.
A through-hull fitting is one part of the exhaust system, not a complete marine installation kit or a guarantee of a safe installation. Have a qualified marine installer assess your boat and follow the instructions for your specific heater, exhaust components and vessel before drilling or operating the heater.
01 / Start with the Exhaust Route
Before selecting a fitting, plan how the exhaust will travel from the heater to the exterior outlet. The available space, hull construction and hose approach will help determine whether a straight or angled fitting is appropriate.
Do not select an outlet location simply because it is easy to reach. Ask your installer to assess water exposure, the vessel's operating conditions, nearby openings and the risk of exhaust entering occupied areas. Required clearances, routing limits and water-protection arrangements must come from the relevant equipment and vessel instructions.
Illustration: an angled skin fitting and a raised exhaust-hose route. The inset highlights water-ingress considerations; it is not a dimensioned installation specification or a layout suitable for every vessel.
02 / RP13 or RP12: Which Fitting Suits Your Layout?
These are alternative fitting options, not two parts that must always be installed together. Choose the geometry that suits the approved exhaust layout for your boat.
| Feature | RP13 | RP12 |
|---|---|---|
| Fitting shape | Angled / bent | Straight |
| Listed material | 316 stainless steel | Stainless steel |
| Listed connection size | 24mm fitting | For 24mm inner-diameter hose |
| Layout consideration | When the hose approach calls for an angled connection | When a straight connection suits the hose approach |
| Before ordering | Confirm actual mating dimensions, wall thickness, mounting space and suitability for your specific heater and vessel. | |
The RP13 product listing specifies marine-grade 316 stainless steel. The RP12 listing specifies stainless steel without identifying a grade, so do not assume the same material specification for both products.
03 / Understand the Through-Hull Mounting
The supplied illustration shows a flanged fitting mounted through a panel using fasteners and gaskets. This helps explain the general arrangement, but it does not determine the correct hole size, sealing method, tightening torque or thermal protection for your boat.
Illustration: exterior flange and mounting arrangement. Confirm the supplied hardware and follow the component-specific installation instructions.
Have your installer confirm the required fasteners, gasket materials, sealing products, hose supports and protection for adjacent surfaces. Do not assume the supplied gaskets or a metal flange alone provide all the thermal isolation or water sealing your installation requires.
Have the completed installation inspected and commissioned by a qualified marine installer, including exhaust integrity, heat exposure, water-ingress protection and possible exhaust recirculation. Use suitable independent CO alarms and follow the heater and vessel safety instructions. If exhaust fumes or a CO alarm indicate a problem, stop using the heater and follow the emergency instructions for your equipment.
04 / Watch a Boat-Installation Reference
Chinese diesel heater install on Northriver
Video by Bryan Waters.
Use this video as a real-world reference, not a substitute for your equipment manuals or a vessel-specific installation assessment. Its inclusion does not establish that the creator used or endorsed the RP13 or RP12 fittings.
Frequently Asked Questions
Do I need both RP13 and RP12?
No. They are angled and straight fitting options. Select the fitting that matches the exhaust layout assessed for your installation.
Will a 24mm fitting fit every diesel heater?
No. A listed size is only one compatibility check. Confirm actual connection dimensions, the heater's exhaust requirements and the complete installation layout before ordering.
Does the fitting prevent all water ingress?
Do not rely on the fitting alone. Water protection depends on the outlet position, exhaust routing, vessel conditions and the arrangement specified for your equipment.
Can I copy the installation shown in the pictures?
The pictures illustrate fitting placement and mounting concepts. Your boat may require a different arrangement, so have a qualified marine installer determine the appropriate design.
Choose Your Through-Hull Exhaust Fitting
Two shapes for different layouts. Confirm the fit and installation requirements before ordering.
ANGLED OPTION
RP13 / 316 Stainless Steel
A bent 24mm through-hull exhaust fitting with 316 stainless steel specified in the product listing. Consider this shape when an angled connection suits your assessed exhaust route.
Shop RP13 Angled Fitting
STRAIGHT OPTION
RP12 / Straight Connection
A stainless steel through-hull exhaust fitting listed for 24mm inner-diameter hose. Consider this shape where a straight connection suits your assessed installation layout.
Shop RP12 Straight FittingReview product dimensions, package contents and heater compatibility alongside your installer's vessel-specific requirements.
