When should we have a Heater exhaust swan neck?

[RogerJolly]

Do we always want a swan neck in our exhaust, even if we have to lower the skin fitting to make room for it?

Or do we only want a swan neck when we can lead the exhaust hose to a higher point than where the skin fitting can be installed?

Can’t see the point of the first one, unless it’s because the swan neck will take time to fill, so the height in the neck will lag the wave height, giving time for wave to pass before flooding starts. Otherwise it’s surely disadvantageous - even if the neck isn’t overtopped, you still have a blockage until the wave passes, where it wouldn’t even reach the higher outlet point if there was no swan neck.

 

[rogerthebodger]

This is generally how Vetus recommend the exhaust layout is

 

[RogerJolly]

Just seeing a red cross mr Bodger. Would that be engine exhaust though, not heater?

 

[Stemar]

Working backwards, exhaust on my boats, heater and engine, have always gone up from the outlet to as high as I can get them, then back down towards the water trap or heater, the idea being that any water that gets in can flow straight back out. ISTM that that's a good idea, even if it does mean the outlet is a bit lower than it might otherwise be. You're never going to prevent water going in from time to time; it won't be a huge amount from a wave slapping the transom, but it's more than you want wandering around your heater.

Any installation that allows the outlet to go below water level when the boat is heeled seems to be a seriously bad idea, but if there were really no alternative, the pipe would need to run uphill to well above the heeled waterline before dropping to the heater.

 

[Plum]

Do we always want a swan neck in our exhaust, even if we have to lower the skin fitting to make room for it?

Or do we only want a swan neck when we can lead the exhaust hose to a higher point than where the skin fitting can be installed?

Can’t see the point of the first one, unless it’s because the swan neck will take time to fill, so the height in the neck will lag the wave height, giving time for wave to pass before flooding starts. Otherwise it’s surely disadvantageous - even if the neck isn’t overtopped, you still have a blockage until the wave passes, where it wouldn’t even reach the higher outlet point if there was no swan neck.

What does the supplier/manufacturer of your heater recommend? What heater do you have? If it's an Eberspacher their instructions for a marine installation say:-

 

[RogerJolly]

Good info, thanks chaps.

Swan neck making more sense now - was over focussed on wave green water, but guess without a swan neck you're in danger from any source of water ingress - splashes, blown in rain, hosepipes etc.

Thinking of installing Autoterm as a reasonable middle of the price range option.

 

[LittleSister]

Yes, swan neck is valuable.

Below is the relevant bit from the commendably clear and detailed Autoterm installation instructions relating to boats (this is additional to the general (vehicle orientated) details about exhausts, which provide info on e.g. silencer placement etc.).

Note that while I've heard some say that you need to have a drain hole in the exhaust pipe if this doesn't have a continuous fall from the heater to the opening to the atmosphere (unlikely to be achievable in most boats), the Autoterm instructions don't require this. Autoterm do say drill a condensate drain hole in the silencer if this is not mounted vertically as recommended (so that condensate can drain down the pipe).