Ducted heating systems

[Neil2]

I wonder if any members of the forum have experience of ducted/blown air heating systems on narrowboats.

 

I presume they are not as popular as "wet" systems because of the difficulty of maintaining heat over long pipe runs, but are there other disadvantages?

 

 

[Alan de Enfield]

We have a 'blown air' eberspacher on our GRP cruiser. and also in the horse trailer.

 

The problem tends to be the electrical consumption. The one on the boat is a CONTINUOUS 10 amps, is 8Kw output and has 6 vents.

 

The horse trailer one is much smaller (1.9Kw) with a single 'vent'

[NMEA]

I have fitted dozens, but only a handful on narrowboats where wet systems are more popular and could say exactly the opposite if we were talking seagoing boats. Advantages: rapid warm up, drying fresh air capability and can be used for ventilation in summer. Disadvantages: No water heating capability, slight amount of noise from the vents, difficulty in installation due to the duct size. The duct length can also be a bit of an issue, heat loss can be largely negated by using Thermoduct insulation. Modern ones are as frugal on power as the ubiquitous Thermo Top.

[MtB]

We have a 'blown air' eberspacher on our GRP cruiser. and also in the horse trailer.

 

The problem tends to be the electrical consumption. The one on the boat is a CONTINUOUS 10 amps, is 8Kw output and has 6 vents.

 

The horse trailer one is much smaller (1.9Kw) with a single 'vent'

 

 

I have an ancient Webasto warm air blower in my boat and it works very well (apart from the appalling racket the exhaust makes outside).

 

It draws about 15A during the initial ignition phase, but drops to something quite managable like 2 or 3A once running in 'slow' mode having warmed up the bote.

[mross]

What size duct would you use on a 'newbuild' narrowboat, ideally?

Edited October 1, 2016 by mross

[MtB]

I'd like to find a way to quietne the exhaust if anyone has any bright ideas. The exhaust tube is flexible stainless tube abot 30mm in diameter, so a silencer from a modern Webasto is about 6mm too small in diameter.

[mross]

I wonder if you could fit a wet exhaust but with the outlet above the waterline, ie with a trap.

[MtB]

What size duct would you use on a 'newbuild' narrowboat, ideally?

 

Mine uses duct about 4" in diameter, but I suggest downloading the installation manual for whichever heater you fancy using for guidance on what to use for your boat.

 

The hard bit will be calculating the heat loss of your boat in order to size the heater.

I wonder if you could fit a wet exhaust but with the outlet above the waterline, ie with a trap.

 

 

No. It would feck up the airflow and combustion.

 

Silencers are available for the modern ducted air heaters.

[Tiggs]

I think the issue with ducts in narrowboats is that they take up space, and that is one thing we have very little of. Certainly any need for ducts 4"x2" say, would put me off if I could use 2 15mm pipes instead.

[MtB]

I think the issue with ducts in narrowboats is that they take up space, and that is one thing we have very little of. Certainly any need for ducts 4"x2" say, would put me off if I could use 2 15mm pipes instead.

 

 

Except that Nick recently pointed out wet systems require 22mm pipes. More than twice the space of 15mm!

[mross]

I think a 2x4 ducted system under the gunwhale would take less space than radiators. My boat has skirting radiators which are a good compromise. Has anyone got under floor heating (plumbed)?

[Robbo]

I think a 2x4 ducted system under the gunwhale would take less space than radiators. My boat has skirting radiators which are a good compromise. Has anyone got under floor heating (plumbed)?

. You get around 100watt per square metre for UFH, on its own it won't be enough especially on a narrowboat.

[NMEA]

I'd like to find a way to quietne the exhaust if anyone has any bright ideas. The exhaust tube is flexible stainless tube abot 30mm in diameter, so a silencer from a modern Webasto is about 6mm too small in diameter.

That's a pretty old beast mike, maybe a HL model which will be 28mm, if so then I reckon something in the Mikuni silencer range may well suit it. http://www.mikuniheating.com/Details.cfm?ProdID=106

What size duct would you use on a 'newbuild' narrowboat, ideally?

80mm or 90mm for the size of heater that would be required + duct insulation so allow around 110mm

Edited October 1, 2016 by NMEA

[MtB]

That's a pretty old beast mike, maybe a HL model which will be 28mm, if so then I reckon something in the Mikuni silencer range may well suit it. http://www.mikuniheating.com/Details.cfm?ProdID=106

 

 

Thanks!

 

Yes 'tis an HL32, works brilliant!

 

Exhaust outlet spigot is 29.9mm diameter, I've just measured it. Stainless flexi is prolly 30mm ID.

 

That exhaust you link to looks great but 2mm smaller at least, and that's too small when it comes to connecting to a 29.9mm stub outlet!

[Alan de Enfield]

 

 

I have an ancient Webasto warm air blower in my boat and it works very well (apart from the appalling racket the exhaust makes outside).

 

It draws about 15A during the initial ignition phase, but drops to something quite managable like 2 or 3A once running in 'slow' mode having warmed up the bote.

 

My Eber D8LC is 115w continuous and 330w at start up.

 

 

[Neil2]

I think the issue with ducts in narrowboats is that they take up space, and that is one thing we have very little of. Certainly any need for ducts 4"x2" say, would put me off if I could use 2 15mm pipes instead.

 

It depends on the design of the boat - what got me thinking about this is the near impossibility of siting rads where they are needed on our boat. OTOH I can see how easy it would be to install ducting with the amount of dead space under furniture etc.

[Tiggs]

 

 

Except that Nick recently pointed out wet systems require 22mm pipes. More than twice the space of 15mm!

Yes 22mm (or more) for gravity systems, 15mm ok if its pumped. Depends on if you have power to pump with.

 

 

I think a 2x4 ducted system under the gunwhale would take less space than radiators.

 

Yes, the advantage is you don't need radiators at all and leaks shouldn't cause damage.

 

Come to think of it why don't narrowboat owners have more ducted systems?

 

Maybe it's because they tend to dry the air and affect breathing?

[Neil2]

Yes 22mm (or more) for gravity systems, 15mm ok if its pumped. Depends on if you have power to pump with.

 

 

 

Yes, the advantage is you don't need radiators at all and leaks shouldn't cause damage.

 

Come to think of it why don't narrowboat owners have more ducted systems?

 

Maybe it's because they tend to dry the air and affect breathing?

 

I've heard folk say it's a "dry heat", but surely that would be a Good Thing on a boat? Somewhere else I read a post suggesting damp was more of a problem than cold in the winter.

[MtB]

Yes 22mm (or more) for gravity systems, 15mm ok if its pumped. Depends on if you have power to pump with.

 

Excellent. I learn more and more stuff on here every day!

[NMEA]

 

Excellent. I learn more and more stuff on here every day!

I would certainly unlearn that one Mike, at least when dealing with evaporator heaters such as Webasto and Eber, they require 22mm feed and return, using 15mm on a new system could easily lead to a warranty rejection, factory training seminars and the Marine install manual are very clear on that point.

 

It depends on the design of the boat - what got me thinking about this is the near impossibility of siting rads where they are needed on our boat. OTOH I can see how easy it would be to install ducting with the amount of dead space under furniture etc.

I would agree if it were possible to get ducting of the right shape, cross section and temperature rating which could run down one side of a narrowboat but unfortunately most ducting of that shape simply will not cope with the temperatures.

[ditchcrawler]

I would certainly unlearn that one Mike, at least when dealing with evaporator heaters such as Webasto and Eber, they require 22mm feed and return, using 15mm on a new system could easily lead to a warranty rejection, factory training seminars and the Marine install manual are very clear on that point.

I would agree if it were possible to get ducting of the right shape, cross section and temperature rating which could run down one side of a narrowboat but unfortunately most ducting of that shape simply will not cope with the temperatures.

I thought we had done that one this week already, or did I dream it. Was it using plastic pipe?

[Richard10002]

I've got a Truma Gas Warm Air and Water Heater. The ducts run along the floor on one side of the boat with a couple of openings in bedroom and lounge, and one each in the kitchen and bathroom. Fairly unobtrusive. On my previous seagoing boat I had an ebespacher Diesel warm air heater, which was equally unobtrusive - the ducts ran behind furniture and in voids. It only heats enough water to wash the posts, or have a good wash - not enough for a shower - I have a Rinnai for that.

 

The Truma is really only powerful enough to take the chill off, (which is what I use it for), and I think it uses a lot of gas - I have a Boatman stove for proper heating.

 

The eberspacher was good enough and frugal enough to keep me warm when the marina at Glasson Dock was iced over in the depths of winter. Like Mike, the exhaust was noisy for the neighbours, but I didnt notice it down below, even though I slept in an aft bunk, over the heater, and close to where the exhaust exited the stern.

[NMEA]

 

 

Thanks!

 

Yes 'tis an HL32, works brilliant!

 

Exhaust outlet spigot is 29.9mm diameter, I've just measured it. Stainless flexi is prolly 30mm ID.

 

That exhaust you link to looks great but 2mm smaller at least, and that's too small when it comes to connecting to a 29.9mm stub outlet!

Even earlier than I thought then, in that case one of these would suit http://www.melloronline.co.uk/Heater_Installation_Accessories_/5240/Marine_Exhaust_System_2.25m_with_Integrated_Silencer_30mm.html By the way, I have a good selection of new old stock hard to get service parts for the HL range if you ever have the need need.

[Neil2]

I've got a Truma Gas Warm Air and Water Heater. The ducts run along the floor on one side of the boat with a couple of openings in bedroom and lounge, and one each in the kitchen and bathroom. Fairly unobtrusive. On my previous seagoing boat I had an ebespacher Diesel warm air heater, which was equally unobtrusive - the ducts ran behind furniture and in voids. It only heats enough water to wash the posts, or have a good wash - not enough for a shower - I have a Rinnai for that.

 

The Truma is really only powerful enough to take the chill off, (which is what I use it for), and I think it uses a lot of gas - I have a Boatman stove for proper heating.

 

The eberspacher was good enough and frugal enough to keep me warm when the marina at Glasson Dock was iced over in the depths of winter. Like Mike, the exhaust was noisy for the neighbours, but I didnt notice it down below, even though I slept in an aft bunk, over the heater, and close to where the exhaust exited the stern.

 

That's an interesting insight, I had wondered about those Truma combi things which seem very popular with the caravan/motorhome trade.

[MtB]

 

That's an interesting insight, I had wondered about those Truma combi things which seem very popular with the caravan/motorhome trade.

 

A boat is a lot bigger inside than yer average caravan or motorhome for which they are designed.

I would certainly unlearn that one Mike, at least when dealing with evaporator heaters such as Webasto and Eber, they require 22mm feed and return, using 15mm on a new system could easily lead to a warranty rejection, factory training seminars and the Marine install manual are very clear on that point.

 

I had already unlearned it and posted much the same as you in post 10.

 

I was being fascetious with that nice Mr Tiggs as he obviously didn't read the thread before posting wrong information.