Forums, Internal Fixtures and Fittings, Hot air heater ducting

George Isted at 28/10/2014 15:25:28
When fitting a hot blown-air heater (Webasto, Eber, etc) and you want to have heating outlets in the middle and forward cabin do you run the ducting down the port side or the starboard side of the boat?

I’m assuming the heater is fitted in the larger port-side cockpit locker as that makes fuel-in and exhaust-out easy.

If running the ducting down the starboard side I guess it will either run from the heater through the engine bay or around the stern of the boat before going forward.

Running the ducting up the port side would be easier but would require cutting holes in the GRP galley locker/cool box liners and I don’t really want to do that.

Thoughts?

Silver Harmony at 10/11/2014 21:34:39
My Eber is in the port side cockpit locker as you suggest, tucked up inside the cockpit coaming. Nicely out of the way and tricky but not impossible to get in and out. I have a small hatch in the coaming to access the glow plug.

My hot air ducting comes down the port side. There is enough space behind / below the liners for the galley lockers. I have a Y joint in the locker aft of the saloon table and the first outlet is there. The 2nd outlet is at the forward end of the heads cabin, below the sink. The main disadvantage with this routing is that the ducting gets in the way of servicing the heads seacocks.

Combustion air is drawn directly from the cockpit locker. Air for the cabin is drawn from the starboard side cockpit cubbyhole via a duct round the stern inside the lazarette. Having the heating air intake outside makes the heater very effective at drying the boat but is less efficient at actually heating than drawing from the cabin.

My exhaust runs out to the transom via the lazarette. It gets very hot and even with lots of lagging anything plastic that touches it (including fenders and ropes) will melt. Also, reaching the transom skin fitting to get the exhaust pipe on and off is a long and uncomfortable stretch.

I have a love/hate relationship with mine. It’s great when it’s working but it’s somewhat temperamental and replacement parts are very expensive. To be fair it is probably getting on for 30 years old. If I was fitting a new one I would use the finest quality marine grade wiring I could find, and add some waterproof connectors to the loom to make getting the heater unit in and out easier. I would also oversize the main power cables as a lot of the problems with them seem to be down to voltage drop in the wiring. Eberspachers and their mounting fasteners are not stainless so grease the threads if you ever want to get it out again.

If you don’t already have one a carbon monoxide detector is a good idea otherwise if the exhaust leaks or the wind is blowing it back towards the hot air intake the heater can fill the boat up with CO.

Alastair D Pugh at 11/11/2014 09:58:21
And now for the other side …….
Mine is in the stern locker tucked up on the starboard side with the mounting bracket on the bulkhead. Heated air duct goes down below cockpit, through longtitudinal bulkhead, under pilot berth, through the under chart-table bin, Y-branch under saloon berth to outlet and forward through hanging locker to fo’c’sle. Combustion air is from locker, heating air is from a duct laid along the lid of the pilot berth. Fuel is tee’d off the tank sight tube. Getting it in and out is not too difficult once you’ve sussed out the angles for the hose.exhaust clip screws – one tip is to block the gap at the bottom of the bulkhead, it makes picking up dropped washers etc. so much easier. Like Robert’s mine was fitted when I got the boat.

I second the CO detector! I got very ill when the exhaust split on mine – that was before I ducted the air intake forward.

Alastair

George Isted at 11/11/2014 11:08:33
Thanks both for your messages, I already have a CO detector in the boat.

I have now managed to cut ducting holes up the port side, there is space behind both the GRP locker liners in the galley, although I have had to take a corner out of one to bring the ducting down to the under-seat berth at the aft end of the table.

Alastair – good tip to take a Tee off the fuel sight tube as that will save me drilling a hole in the top of the tank – not easy in situ.

I am having a custom sized wiring loom made up with oversized tinned cabling so hopefully that will reduce the likelihood of wiring issues.

I can see why many owners go for the smallest heater from webasto/Ebber as I have the medium sized one (3500w output) that is a bit physically bigger and it’s a very tight fit.

Re the exhaust – how high on the transom, the higher it is the less of a goose-neck bend can be put into the exhaust so I was going to go for a middle to low position on the transom and hope the height of the goose-neck will keep any water away from the heater.

Cheers

George

waratah912 at 11/11/2014 18:47:42
A survey of Lymington Contessas by rowing dinghy showed most were low on the transom, so that’s where I fitted mine. This gives you a longer gooseneck which I would imagine reduces the possibility of water ingress. Water doesn’t much like flowing up narrow pipes!

Silver Harmony at 11/11/2014 19:11:29
I agree a lower exhaust outlet makes sense. The inside end of the skin fitting angles up too so if the fitting is too high the exhaust hose will hit the deck. The spiral wound flexible pipe doesn’t like sharp bends. Pick a site you can reach from inside because the flexible exhaust hose doesn’t last forever. You can also get elbows for the heater end that have a drain point which are maybe worth considering.

Good luck with the install. The muted roar of ignition followed by the blast of hot air at your feet will make all the time spent jammed in the cockpit locker feel worthwhile!

George Isted at 11/11/2014 19:18:50
Thanks gents, having done a trawl of online pictures of Co32 transoms I have concluded that low and central-ish on the transom is the best location, allowing more height inside.

Cheers

waratah912 at 11/11/2014 19:37:36
For those cold night watches you could also consider a vent in the cockpit, for a modern take on the hurricane lantern between your feet and sailbag over your knees :)
Yes, I’m from the East Coast!

waratah912 at 11/11/2014 20:46:38
Another consideration, oil soaked lagging is a major source of fire in refineries, so I sleeved mine in flexible aluminium ducting over the top of the lagging and sealed the ends with aluminium foil tape. You need bigger holes if you’ve got to go through a bulkhead, but it reduces the chance of fire significantly and of chloride induced stress cracking if you get seawater on the lagging, neither if which are ever going to happen – right???

Silver Harmony at 11/11/2014 21:09:32
I used ExoWrap on mine. ASAP supplies sell it. It’s basically lagging with an aluminium foil backing, specifically intended for “high temperature surfaces in vessel engine rooms.”
http://www.marinetapes.com/index.php/marine-division/14-exowrap%C2%AE-insulation-system.html
http://www.asap-supplies.com/search/exowrap

I wouldn’t worry about stress corrosion cracking though. I’ve replaced my Eber exhaust twice and both times it was plain old corrosion that caused it to fail. Maybe next time I’ll try and source a titanium pipe.

George Isted at 12/11/2014 09:38:04
Good tip on the lagging, the exhaust will run past the back of the gas locker (that obviously doesn’t want to get hot!) so I will look up Exowrap.

Keny at 17/11/2014 13:13:54
Hello George
Mine is actually under the floor in the wet locker where it can warm up the clothing. Minimal ducting, easy to get at and very high gooseneck. Exhaust is through the hull and it works well if a little noisy.
Inlet/outlets are in the middle of the boat and one in foreward berth.
keny

waratah912 at 18/11/2014 22:13:22
For fuel supply, if you have a separate primary fuel filter, typically the CAV 296, it has a second filtered outlet and you can feed your heater with clean fuel. Just one less thing to go wrong if you ever get dirty fuel or diesel bug.

Richard Ritchie at 18/11/2014 23:27:42
Ideally have a separate stop cock in the fuel line to heater, since this tends to be snaking round locker edges so vulnerable. Otherwise could loose engine through damage to this pipe. On Mikumi heater this can be done with a solenoid so off unless heater in use.

George Isted at 20/11/2014 10:38:49
[QUOTE=waratah912] For fuel supply, if you have a separate primary fuel filter, typically the CAV 296, it has a second filtered outlet and you can feed your heater with clean fuel. Just one less thing to go wrong if you ever get dirty fuel or diesel bug.

Thanks, not possible with my filter and I’m not convinced this is a 100% good idea as an air-leak in the supply to the heater could result in air being drawn into the main engine filter if there was any restriction (slight blockage in tank outlet) in the supply feed, unlikely but possible. In the short term I’m putting a Tee into the bottom of the tank sight tube and will run off that.

Alan Dixon at 14/03/2016 14:10:54
I am seriously considering fitting an heater and read with interest the various strategies for mounting and leading the ducting.
I favour the ducting on the Starboard side as being slightly easier, keeps heat away from the bins where I store food, and a little heat loss in the wet locker would not be a bad thing.
Has anyone used the area above the quarter berth to house a heater, it would give reasonable access to the stern for the exhaust, combustion air could be drawn from the side cubby hole.
any input / disadvantages dangers gratefully received
Alan

George Isted at 14/03/2016 14:24:01
If you ever plan to use the quarter berth for sleeping I wouldn’t put the heater above it. It’s not that noisy but would be intrusive if sleeping.

I have a Webasto 3500ST fitted with two outlets. Maybe I’m getting soft but I would not want to have a boat without a heater now. Toasty :-)

waratah912 at 14/03/2016 16:57:45
I wouldn’t mount it above a berth, slight exhaust leak and you’ll be sleeping forever.
Not sure there’s a good answer – they are all a compromise, I mounted mine (D5W – wet) behind the engine, which makes it an absolute pig to maintain from the quarter berth, but keeps all of the hot stuff, fuel consumers and exhausts in one compartment.
I didn’t want it in the cockpit locker as :
a) at that time the gas bottle was in there too
b) there’s always the possibility of damage to the fuel pipe or damage from the exhaust / fire risk if the lagging becomes damaged and unseen.

Don’t be tempted by the silencers for sale on eBay – they are only suitable for external use, the seems are only spot welded and leak exhaust gases.

caramorsimon at 21/04/2016 22:37:11
caramor has heater ducting on the starboard side.
the ducting runs across the floor by the cockpit seacocks, through the engine bay and under the quarter berth.
A corner taken out of the stbd engine access panel gets it under the quarter berth from where it runs forward.
I could have planned a false floor in the outboard bin under the chart table, but I took it high over that space, forward behind the saloon seat back & then down into the underseat lockers. It meant reshaping one corner of the berth cushion & taking the corner out of the locker lid but I didn’t want to lose space in the locker under the chart table.
I have a pair of outlets (each end of the stbd saloon berth) before it goes through the wet locker to the forepeak.
toasty boat.
I remain paranoid about anything touching the hot exhaust hose though – even lagged its pretty hot..

Alastair D Pugh at 22/04/2016 09:25:03
My D2 exhaust is lagged and hidden inside a length of 60mm ducting. It gets warm but not enough to melt plastic. I replaced my exhaust again this winter. It looked a bit corroded but ok until slight flexing caused it to break.
My exhaust outlet is about 9" below the top of the transom and I now plug it when I leave the boat ‘cos I found it full of salt water. Calmac in their wisdom now run smaller ferries on the Gourock/Dunoon run which kick up a very high short pitched wash that can actually wash up over the transom if the boat is lying stern to and obviously my swan neck isn’t enough.

caramorsimon at 22/04/2016 21:51:08
alistair – I have the usual exhaust hose/wrap/outer metal wrap – have you added further lagging & if so what materials did you use?

Alastair D Pugh at 23/04/2016 14:10:56
My lagging is nothing fancy. Just an asbestos-like woven tube (eBay – Eberspacher Exhaust Lagging) over the stainless flexible pipe all covered with an offcut of 60mm aluminium ducting left over from fitting.

moongirl at 13/02/2017 22:25:40
Some food for thought! My boat has the remains of a heater fixed to the ‘wall’ between the cockpit and large locker – easy to get to I guess but I would have to take of stowage ie no melting type objects in touch – lazerette could get quite full causing problems with trim! The boat came with a new and as yet unfitted Airtronic D4 which will come in handy on those colder nights (Christmas Rally?) it seems that the ducts run down the starboard side so I will stick with that arrangement I think. The ducting is not very good and needs replacing – as part of my job I design MHRV ventilation systems for Houses using some robust 75mm semi flexible ducting that doesn’t crush and has a reasonable bending radius – prefabricated bends are available as well although I note that the Instructions say ‘keep’ bends to a minimum.
I will have a good look at the boat next month and give some more thought to it.
On Muscadet de Havelet (the boat I race on) the heater is tucked right up under the deck over the port locker – another option maybe. I haven’t checked to see if there is a site tube on my tank if not then I will have to wait until the boat is back in the UK maybe this Winter coming if I have had enough of cruising Norwegian and Swedish waters!

moongirl at 13/02/2017 22:29:31
Following my previous post I think the Installation Instruction say no gravity feed. This implies that the heater must be higher than the top of a fuel pipe tee into the engine feed. Again measurements needed next month!

moongirl at 13/02/2017 22:30:37
It’s late! I think I meant above the tank full level

moongirl at 13/02/2017 22:33:18
It must be bed time – after a very busy day! The existing heater is in fact in the lazerette!