Hot air or Hot water heating

Z

zambant

Well-Known Member
Joined
25 Jan 2010
Messages
430
Visit site
I have a Moody 345

Cant decide on installing either

1. diesel fuelled hot air heating system (Erber or Webasto )

or

2. diesel fuelled hot water system (Erber / Webasto) feeding radiators / fan blown matrix heaters and possibly heating up the hot water tank.

Anyone done it and could share their views please? I am struggling with the pro’s and con’s
Thanks
John
 
I'd go for blown hot air on a boat of that size, unless you really feel the need for loads of hot water.

A water system adds additional complications and I've only seen them on larger boats and live a boards.

Another vote for Mikuni as an option.
 
Ducted hot air is very simple, and the heat is almost instantaneous. Downside is that the ducting takes up a lot of space, and unless insulated, loses heat into places where you may not want it.
Hot water is slower to react, but the pipes take up much less space. If using fan blown heater matrices, you have to consider the extra electrical demand.
 
Chum of mine was moaning about reliability and costs of fixing his heating....assumed it was warm air.....nope it was the Eber wet system.
 
Hot air. If you go for hot water, there's a considerable extra power requirement for the fan motors in the matrix heaters.
 
pvb said:
Hot air. If you go for hot water, there's a considerable extra power requirement for the fan motors in the matrix heaters.
Click to expand...

However, if you install a water-to-air system with heater battery (HX) very close to the space, there is significantly less duct resistance to overcome and therefore fan losses are not that significant, assuming you don't need long duct runs to duct-in lots of cold fresh-air!

A small one row HB may have a pressure drop as low as 25Pa, which equates to a duct run length of say 15m (normally 1Pa/m but on boats they tend to use smaller size ducts at higher design pressure drops that as a result result in higher velocities and sometimes noise). You will in any case have a pressure drop through the Eber air HX.

So as far as the extra fan energy is concerned, it may be as little as an additional resistance of say 12.5Pa, that's the same amount of energy you need to exert when sucking beer up a straw less than 2mm! So not that much!

However, that being said, if I could not stretch to a reverse cycle heat pump, I would opt for air. Why? It has a lower thermal heat capacity compared to water, so when heat is applied to it, it heats-up more rapidly which is useful on a boat!

Water is best if you have very little room for routing ductwork.
 
I have been an advocate of coolant based systems for some time now and have fitted quite a number and being London based service the things on narrowboats and big barges on an almost daily basis. Like all heating systems it is a case of what is appropriate for the size, seasonal usage and expectations and requirements of the end user.
Coolant based systems. observations. more flexibility in the site of the boiler which makes life a little easier and can reduce noise considerably, no need to consider exhaust runs near the air intakes, coolant carriers easier to run, I use Hep or similar in narrow boats and large boats but with smaller yachts and mobos it is often easier to use heater hose or a mixture of hep and hose. They have the capability of being able to be incorporated into the propulsion engine for free heat whilst cruising, possibly not so much with a yacht obviously. To get the best you really need radiators of the type not suited to most yachts but you can use smaller fan assisted radiators like the Kalori Baikal range, used with a variable fan speed can be very quiet indeed and you can safely turn in with the thing running and turn the fans off for peace. I have found that the usual kind of matrix does not perform so well with them. They need careful planning to make sure the correct unit is chosen and "loaded" properly. All in all they are a superior system to blown air heating but only if appropriate to the vessel and usage. A tip that may help with your decision is to forget about the install except for the rads, if you can find space for them and they add up to enough of a sink to load your chosen heater then you will be happy with it. Should you decide to go for it, then for reliability, ease of service and cost I would choose eithe a Webo Thermo Top 4kw or a Mikuni MX40, anything bigger would not be loaded by the rads that would probably be needed on a 34 footer enough in my view, except possibly a mobo with large glass area. As this is PBO I guess I should say that it will cost you more than a similar air system, though the good news is that the Webo marine kits RRP has just been reduced by a couple of hundred until the end of 2012.
 
Last edited:
John100156 said:
However, if you install a water-to-air system with heater battery (HX) very close to the space, there is significantly less duct resistance to overcome and therefore fan losses are not that significant, assuming you don't need long duct runs to duct-in lots of cold fresh-air!

A small one row HB may have a pressure drop as low as 25Pa, which equates to a duct run length of say 15m (normally 1Pa/m but on boats they tend to use smaller size ducts at higher design pressure drops that as a result result in higher velocities and sometimes noise). You will in any case have a pressure drop through the Eber air HX.

So as far as the extra fan energy is concerned, it may be as little as an additional resistance of say 12.5Pa, that's the same amount of energy you need to exert when sucking beer up a straw less than 2mm! So not that much!
Click to expand...

All great in theory, but you've missed the point. A hot water system uses more power than a hot air system. As an example, an Eberspacher D4 air heater uses 40W. The equivalent Eberspacher Hydronic 4 water heater uses 48W, plus the power needed by the matrix fans.
 
Air or Coolant

Great post!

I'm fitting out a small steel boat. I lived on a small fibreglass boat for a couple of years and I won't be going for the blown air on this fit out! I know about the energy difference, the possible weight and inconvenience/complication. However, blown air is very 'dry' heat, noisy and on the liveaboard, despite moving the intake and exhaust positions, impossible to get totally 'clean' air. I know LOTS of people don't have these problems but I won't be going back to blown air. After a long period of time all my clothes stank of exhaust fumes. Not nice. I was however, warm.

I don't like the look of the 'heater matrix' fan options offered but I don't see why a different radiator option could not be fitted - under floor boxes for instance.

Very interested in experiences of non matrix radiator installations.
 
So less than 15ah over a 24hr period (less on an 24v system and assuming full chat) a small price to pay for the many advantages, assuming the system is the correct option and will perform and provide the users needs better than forced air an extra battery in the system is hardly the end of the world, except that you have to buy it I suppose. There is often no need for any extra fan consumption on many installs if properly planned.
 
pvb said:
All great in theory, but you've missed the point. A hot water system uses more power than a hot air system. As an example, an Eberspacher D4 air heater uses 40W. The equivalent Eberspacher Hydronic 4 water heater uses 48W, plus the power needed by the matrix fans.
Click to expand...

However, for 5KW the current drain on a 12V system is heavily in favour of the hydronic system

Eber D5 airtronic on high - 6.3A

Eber D5 hydronic on high - 4.2A.

Obviously if radiators and towel rails are used there is no further battery power required on the wet system.

If fan matrix units are used the Eber Helios units are very frugal on amps

Helios 2000 on high (2KW) - 0.9A
Helios 4000 on high (4KW) - 1.8A.

It should also be noted that the cost of a D5 airtronic 4 outlet system is approx £2,200 while the cost of a narrowboat hydronic kit (£1,180) plus 3 fan matrix units (not Helios which are pricey) and some hose and plumbing bits is approx £1,700.
 
:)
This is what we use for our heating. Trumatic E 2400 gas heater.
You just set it to the temperature that you need by the thermostat and you have immediate heat its cheap and has low Power consumption at 12 V 0.6 A Plus economical gas consumption (approx. 95% efficiency) reliable whilst on the move or in extreme wind conditions and has thermostat-controlled shutdown and re-ignition.
 
machone said:
However, blown air is very 'dry' heat, noisy and on the liveaboard, despite moving the intake and exhaust positions, impossible to get totally 'clean' air.
Click to expand...

If a process air silencer is used in the air ducting, blown air systems can be virtually silent. Similarly, by routing intake air from outside the boat, there are no smells (unless your fresh air is smelly!).
 
I was rather concerned by the poster who said his boat smelled of exhaust! With a blown air heater the combustion airflow and heated airflow should be isolated from each other and IMHO ideally the heating intake taken from inside the cabin whilst the combustion air intake and exhaust should be external.

Funnily enough I am wondering about a Hydronic unit in a 27ft boat as narrow bore water hoses can be routed to where I want the heat, whereas air ducting is larger than the voids available, so I would have to make my own ducts to fit.

Rob.
 
PVB - I think your point regarding energy has been answered. If we had some more info/images from the OP, we can consider all options and select the best system.

An effective air silencer is usually quite large and it may be difficult to find space for it. As an alternative, you could use acoustic flexible ducting, which will, over a reasonable length provide excellent attenuation and insulation, both solutions will increase duct resistance slightly hence fan power.

If you want a quiet system, its best to size your ducts to provide around 3m/s air velocity. If you can achieve that and use acoustic flexible ducting, you will not hear any duct born air noise.

However, often its the grille noise which is the issue. On boats they often size and fit them where they can, which is often not where they should be! A badly designed grille will cause draughts as higher air velocities impinge the occupied zone and will create noise as it dissipates energy at the outlet!

With regard to recirculating warm air heaters drying the air, that often amuses me. ANY heater dries the air, it expands it in volume and hence its RH reduces! It matters not whether its a 2kW air or a 2kW radiator, psychrometrically the result is the same.....

None of us are really in dissagreement, just attacking it from different angles and giving the reader(s) enough (I hope) to make an informed choice for their specific application!
 
I did spend a very cold winter in Fiumicino with a Swedish Lloyds Register inspector who'd fitted his own hot-water system (with an Eberspacher boiler).
He reckoned the capital cost was about x250% of an hot-air system, most were appallingly badly fitted and the owners didn't get the best result.
Diesel usage was higher than for blown-air system, reliability much greater, electric-usage lower (the matrix fans were thermostatically controlled) and general temperature distribution considerably better - certainly his boat was the most comfortable I've been in.
For him the greatest benefit was constant hot water.

Me I just use a fan heater and avoid cold winters in the boat.
 
I think there are more and better fan matrices on the market than when I installed my system 6 years ago.
It depends on whether it is possible to duct air around the boat adequately, I don't think there was a good way of getting warm air to my forecabin, but hot water was easy to do.

The bonus of hot water for showers and cleaning is worth a lot IMHO.

But the instant hot draught of an airtronic is very nice to have on an autumn sail.

A work colleague has a Land Rover which he drove to Scandinavia. It has both air and water systems, one eber, one webasto. Might not be all that silly on some yachts? But once you get much above 40ft, a generator and fan heaters starts to make sense, with a radiator in the generator cooling system.
 
You must log in or register to reply here.

Share this page

Top