Heating: Water or Forced Air?

SailBobSquarePants

SailBobSquarePants

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Following up on the thread on diesel heaters (OK, I now know what MAKE to go buy!) started by Scotty, I was wondering if people had views or insights as to water/radiators versus forced air installations? What are the pros and cons of each that you have seen? Price wise, it looks that water is a bit more expensive (for the radiators themselves), but the benefit is you get a source of hot water that does not require running the engine inefficiently to heat the calorifier.

Would love to get people's opinions...
 
the water ones, take an age to heat up, 30mins of the air heater being on, the boat is nice and toasty, 30mins of the water one, the radiators are only just starting to get warm.
 
mattnj said:
the water ones, take an age to heat up, 30mins of the air heater being on, the boat is nice and toasty, 30mins of the water one, the radiators are only just starting to get warm.
Click to expand...

This is true, more so with the type with passive radiators, than the type which has fan-coils.

Hydronic (water) heaters have other advantages:

1. Heat is distributed in small water pipes rather than large air ducts, so possible to distribute far and to many points. Quite important in larger boats.

2. Produces domestic hot water besides heat -- a big advantage.

3. Quieter than air heaters, especially the ones with passive radiators. Fan coils still quieter than air-based heaters.

Hydronic heaters have a few disadvantages:

1. Cost

2. Complexity -- pumps, valves, etc.

3. An ethylene glycol water mix to futz around with -- can leak, wants topping up or changing sometimes.

4. As mentioned above, slower to heat up from cold, especially the passive radiator type.
 
We have an Eber D4 to heat a 13m steel yacht. There are two outlets, one in the saloon under the steps and one in the aft cabin. The aft cabin heats up very quickly and the saloon just a little longer. Because the D4 gives a good blast of air, the saloon outlet heats the fore cabin which has saved running the hose under the flooring. Also, even during the winter months 'T' shirts are the order of the day--in fact we have to turn the thermostat down. A D2 was considered but advice from Eber said it would be struggling to heat the whole interior.

We did think about radiators but where would they be fitted? Certainly we have the space but the actual radiators would be in the way. I was on a yacht once which had radiators around the saloon seating, ie just below knee height and I found it uncomfortable with the heat going onto the backs of my legs. Not for us. Blown air helps dry out a boat more quickly and if the heater is maintained, which ours is, then there should be no problems.

dansar
 
dansar said:
We have an Eber D4 to heat a 13m steel yacht. There are two outlets, one in the saloon under the steps and one in the aft cabin. The aft cabin heats up very quickly and the saloon just a little longer. Because the D4 gives a good blast of air, the saloon outlet heats the fore cabin which has saved running the hose under the flooring. Also, even during the winter months 'T' shirts are the order of the day--in fact we have to turn the thermostat down. A D2 was considered but advice from Eber said it would be struggling to heat the whole interior.

We did think about radiators but where would they be fitted? Certainly we have the space but the actual radiators would be in the way. I was on a yacht once which had radiators around the saloon seating, ie just below knee height and I found it uncomfortable with the heat going onto the backs of my legs. Not for us. Blown air helps dry out a boat more quickly and if the heater is maintained, which ours is, then there should be no problems.

dansar
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Remember that hydronic heaters can use fan coils instead of radiators. These are easier to locate than radiators and do circulate air with the benefits you mention, at the cost however of some noise.
 
Dockhead said:
Remember that hydronic heaters can use fan coils instead of radiators. These are easier to locate than radiators and do circulate air with the benefits you mention, at the cost however of some noise.
Click to expand...

Another important consideration for many boatowners is that fan-assisted radiators use a considerable current, making the installation much more power-hungry than forced air systems.
 
Was just reading...

Was just googling this earlier today, and on a narrowboat forum they said that the primary advantage of the water heating kind is that you will USE it during the summer months (for hot water), which helps ensure that it works better - it seems these things don't like to sit idle for long periods.

On my old, narrow beam boat running the air hoses will undoubtedly be a problem, and the water pipes would be a lot easier.

Does anyone know how the fan-assisted radiators for water cooling work with heaters that are under programmable control? How does it know to turn itself on - does it have a sensor for water temperature or flow? Or do I need to manually turn them on when the heater comes on?
 
Dockhead said:
Quieter than air heaters, especially the ones with passive radiators. Fan coils still quieter than air-based heaters.
Click to expand...

I'd disagree with this. Forced air heaters don't have to be noisy. There are silencers available - both for the heated air and the intake air. Carefully installed, noise in the cabin is almost zero. My Eberspacher has a silencer on the heated air duct and it's hard to tell when it's switched on.
 
From a theoretical point of view it would appear that the advantage of the heated air type was the drying action of the heated air passing through and out of the boat.
 
guernseyman said:
From a theoretical point of view it would appear that the advantage of the heated air type was the drying action of the heated air passing through and out of the boat.
Click to expand...

Depends how it's installed. Mine draws in fresh air and heats it, so there is a flow of air in and out. But many people draw the intake air from inside the cabin, so they're just recirculating the same air.
 
I have a mikuni wet system, and am lucky enough to have space for small domestic radiators.
The water pipes were much easier to install and lag that air ducting would have been. It is controlled by a 7 day timer/thermostat with additional thermostats on each radiator.
The radiators get hot within 10 minutes and the system is silent - but I agree that a hot air system may initially heat the cabin quicker.
As I have ordinary radiators, there is no additional electrical load than the small water pump. For me the advantage of having hot water without running the engine far outweighs any advantage an air system could provide.
 
guernseyman said:
From a theoretical point of view it would appear that the advantage of the heated air type was the drying action of the heated air passing through and out of the boat.
Click to expand...

Most are rigged to recirculate air which is already inside the boat. Same with the fan coils used with the water type.

But still, it seems to me that the circulation of warmed air inside the boat definitely does dry it out. The circulation of air by itself gets rid of condensation and dries wet surfaces. I am guessing that water is picked up like this and does actually leave the boat as part of the natural circulation of air (we have dorade vents).

This would be an advantage of not only an air-based system, but also of a wet system with fan coils, compared to a wet system with radiators which does not circulate any air.

Maybe some systems actually draw air from outside the boat. That would be even better from the point of view of drying the boat out. But at the expense of a lot of calories of heat.
 
BGW said:
For me the advantage of having hot water without running the engine far outweighs any advantage an air system could provide.
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+1

This is a really big advantage. Also, a wet heating system not only heats domestic water independently of shore power or running the engine, it heats it a lot faster. Abundant hot water on board is a nice thing.
 
Can I ask people with water-filled systems how easy they are to drain down during winter layup? Or do you fill them with antifreeze?
 
SailBobSquarePants said:
Was just googling this earlier today, and on a narrowboat forum they said that the primary advantage of the water heating kind is that you will USE it during the summer months (for hot water), which helps ensure that it works better - it seems these things don't like to sit idle for long periods.

On my old, narrow beam boat running the air hoses will undoubtedly be a problem, and the water pipes would be a lot easier.

Does anyone know how the fan-assisted radiators for water cooling work with heaters that are under programmable control? How does it know to turn itself on - does it have a sensor for water temperature or flow? Or do I need to manually turn them on when the heater comes on?
Click to expand...

We have a Refleks Diesel stove http://www.lockgate-stoves.co.uk/products/marinestoves/nonvisibleflame/refleks/ which has an internal coil for heating the hot water and Rads. The water is circulated by a small 12v pump which has a temp sensor so only kicks in when the water is upto temp.

For what its worth, There are many complaints on the Canal Forums of the wet version of ebers and webasto's failing.

They are also nicknamed Eardrumbashers & Weblastos

The advantage of the Refleks is its simple, no eletrickery apart from the 12v pump and gives off loads of heat even without the hot water version
 
alan_d said:
Can I ask people with water-filled systems how easy they are to drain down during winter layup? Or do you fill them with antifreeze?
Click to expand...

You run them on antifreeze - it also prevents corrosion of the system.
You can make it very easy to drain down for maintenance by putting a gate valve (or two) in the low points of the pipe work.

Oh - and the point of heating is that you don't have to lay up the boat for winter :-)
 
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