Fitting a heater in a Sun Kiss 47

[Sea Change]

We're heading up to Nova Scotia this summer and I'd like to install a blown air diesel heater. I'm familiar enough with these units and have installed two on previous boats, and helped a friend install his.
I'm aware of the limitations on ducting length, exhaust length, and I'm aware of how hot the exhaust can get.

In an ideal world I'd fit the heater in the engine room or in a stern locker, and run the ducts forward. However my boat's layout doesn't lend itself to that. In typical 80s French fashion, the aft heads/shower is under the bridge deck, between the aft cabins. The aft cabin berths both have tanks underneath them.
So there's no obvious way to get a 70/90mm insulated duct run from the engine room past these obstacles, without building some sort of trunking, which would be a bit of a pain.
I could run the ducting higher up along the side of one aft cabin, possibly sacrificing the storage shelf to do so.

The other idea I had was to abandon the transom mounted exhaust, and run the exhaust up to a metal mushroom vent on deck. But then I started thinking about the downsides of that... you'd have to watch you didn't melt any halyard tails, you'd need to shut it if you expected any water over the deck, and of course open it again if using the heater.

Any thoughts? Any other ways of approaching this?

 

[Minerva]

Could you exit the exhaust on the hull side? Our old CC moody has her heater exhaust just outside the cockpit locker, around 2/3rds of the way back from the bow. Never had an issue with water / wave ingress.

Also at 47ft, are you perhaps at a point where having two, smaller systems, might work? One for the aft cabins and one for the saloon / v berth?

 

[Minerva]

Of course the Gucci option is small blown air heaters for over night in the sleeping cabins and a drip heater fire in the main saloon…

 

[Sea Change]

All valid points, but this needs to be a cheap and cheerful solution, possibly a temporary one.
One of the aft cabins is full of Victron gear so I don't want to heat that space.
A long term, more effective, solution would depend on whether we decide to do a few years of Scandinavian cruising in the future.

 

[AngusMcDoon]

A hydronic one may be more appropriate for that size of boat, especially now that Chinaspatcher have started making them. Bigger burner, but much easier pipes to run, and longer lengths possible allowing you to get heat all the way from the engine room to the front cabin. Forced air radiator units or passive radiators needed which is more of a faff than just a hot air outlet. Another advantage is it's separate way to heat domestic water with a twin coil tank. A summer valve can direct heat just to the domestic water if it's hot weather.

 

[Sea Change]

A hydronic one may be more appropriate for that size of boat, especially now that Chinaspatcher have started making them. Bigger burner, but much easier pipes to run, and longer lengths possible allowing you to get heat all the way from the engine room to the front cabin. Forced air radiator units or passive radiators needed which is more of a faff than just a hot air outlet. Another advantage is a it's separate way to heat domestic water with a twin coil tank. A summer valve can direct heat just to the domestic water if it's hot weather.

That's a compelling argument. We don't have hot water either, and whilst like to fit it. But it's no longer a ~£150 job that can be done in a weekend...

 

[AngusMcDoon]

That's a compelling argument. We don't have hot water either, and whilst like to fit it. But it's no longer a ~£150 job that can be done in a weekend...

You could do it in stages. You can always add more forced air matrix outlets and a dual coil tank later. The system is easy to extend once the boiler is in. The kits come with some circuit pipe and a circulation pump, but no outlets. Here's a 4kW outlet...

Siroco Water Heater Matrix Tenere 2 (Grill) Low Noise 3 Speed Blower 12v 4.2kw Black, Night Heater Kits, Eberspacher, Webasto, Mikuni, Durite

Fitting the boiler and a single matrix output should be doable in a weekend if access is ok. Once the boiler is in the circuit pipes are easy as they are flexible rubber things with Jubilee clip joints. They are pretty bendy so can be poked around and behind things - easier than an air duct. A simple small header tank at the high point is needed like an engine coolant tank.

You can also get single matrix multiple output units that are fitted to trucks where you attach ducts to the outlets to pipe to different areas.

 

[geem]

We have a Webasto hydronic heater. I swapped our old tired calorifier for a nice new highly insulated one with twin coils.
Its great for hot water but the heating side of it was a bit of a let down. The fan coil units are noisy and demand quite a bit of fan power if you are running 4 of them like me. Also, there is a lot of pipework, tees, hose clamps, elbows, wiring, control panel to fit. Its not a cheap job. The old Eberspacher fan blow heater was far quieter and pretty adequate. It just didn't do hot water. The ductwork was a pain to route and insulate and my ducts rotted out after a few years. I had lovely hot bilges but not so much in the cabin.
No option is ideal but the water based system might be easier to fit. Just make sure you over size the fan coil units or install ore of them