Sizing diesel heater

[Ceirwan]

I'm looking to add a diesel (hot water) hydronic style heater to my boat, it's currently got a 4kw Eber blown air, & while its a nice enough system, it only heats the aft end of the boat, and due to layout & design of the boat, its basically impossible to get the hot air piped to the forecabin without either having the heating duct visible in the main cabin, or cutting holes in the hull frames. Neither of which is an option.
An added advantage will be hot water from the system as well.

My question is purely about sizing, Eber & Webasto offer some rule of thumb guides, but I was hoping for some 'real world' experience.
The boat is 36 feet, fairly average volume in side, fibreglass, sailing boat, heating is for the UK winter.

The options seem to be 5KW or 9KW water heaters, the current air one is 4KW, but I'll be heating water as well & also the forecabin, I'm not sure that bigger is always better as I don't want to coke up the heater by not running it hard enough. The smaller heaters are cheaper as well, but that's not the main consideration for me.
Does anyone have some real world experience they can offer?

 

[B27]

The problem tends to be the radiators or matrices.
Getting even 4kW out of the circuit into the air may be quite a challenge when retrofitting a boat.
Also the matrices start using a lot of amps at full blower.

A useful comparison is a mains 2kW fan heater. I ran one on those in a 28ft boat in January a while back, it takes a while to warm the whole boat from cold, but keeps it fairly warm steady state.
But if you start opening hatches to dry stuff the sky's the limit.
The heater in a small car is a few kW, a boat is much bigger than a car. But you rarely use full power.
The 4kW units are popular for limo's in sub zero climates.

 

[Ceirwan]

I've seen some people using computer fans to reduce the current draw of the heater matrices.
Good idea with the fan heaters, using that analogy, I probably would need about 5kw on a cold day to heat the whole boat, unfortunately its a bit too warm to do a test.

 

[PaulRainbow]

I've seen some people using computer fans to reduce the current draw of the heater matrices.
Good idea with the fan heaters, using that analogy, I probably would need about 5kw on a cold day to heat the whole boat, unfortunately its a bit too warm to do a test.

I would not fit any fans, i'd put radiators in. I've worked on boats with matrices and they never seem to work particularly well.

 

[B27]

I would not fit any fans, i'd put radiators in. I've worked on boats with matrices and they never seem to work particularly well.

Yes, radiators are great, when you can fit them in, which is easier on narrow boats, power boats and very big boats!

But 4kW of rads is a lot of metal at 80degC or something. Look at the wattages of domestic rads.

I'm told the matrices are better than 10 years ago, DYOR.

In reality, I think ebers get by running on a fairly low duty cycle, provided you can avoid short cycle times. The calorifier and possibly engine, can act as a heat store to slow the cycle time.


Before Chinaspachers came along, wet ebers using secondhand units from car breakers were a well trodden path, so there should be knowledge if you trawl back through this forum and others?

 

[PaulRainbow]

A thread here about this subject, note the posts about the power consumptions of systems with matrices : Planar or even Chinese ! Diesel hot water /heaters

 

[PaulRainbow]

I'm looking to add a diesel (hot water) hydronic style heater to my boat, it's currently got a 4kw Eber blown air, & while its a nice enough system, it only heats the aft end of the boat, and due to layout & design of the boat, its basically impossible to get the hot air piped to the forecabin without either having the heating duct visible in the main cabin, or cutting holes in the hull frames. Neither of which is an option.
An added advantage will be hot water from the system as well.

My question is purely about sizing, Eber & Webasto offer some rule of thumb guides, but I was hoping for some 'real world' experience.
The boat is 36 feet, fairly average volume in side, fibreglass, sailing boat, heating is for the UK winter.

The options seem to be 5KW or 9KW water heaters, the current air one is 4KW, but I'll be heating water as well & also the forecabin, I'm not sure that bigger is always better as I don't want to coke up the heater by not running it hard enough. The smaller heaters are cheaper as well, but that's not the main consideration for me.
Does anyone have some real world experience they can offer?

Also look at the Planar hyrdonic units, lot less money than Eber and Webasto

 

[mrangry]

I have a hot air heater fitted just now on a 44ft yacht but only have an outlet in the main saloon, to have further outlets would be a major pain due to ducting diameters. I have bought a hydronic heater and a couple of 12v plinth heaters which I bought unused as a job lot from someone and hope to fit it this winter. Whilst I cannot comment on its efficiency as I have still to fit it, the plinth heaters are stated to consume 5 watts per hour and the system will be piped with 19mm auto heater hose.

 

[ChromeDome]

To avoid ducting mayhem I installed two heaters. A 2 kW Webasto for below (heads and cabins, struggling when cold) and a Hcalory 5 kW for the main cabin & pantry.
The 5 kW, app managed and with automatic performance setting, going low when approaching set temperature, is a true master.

Air only as we've use shore power for room and water heating in the marinas, and engine heating while under way.

 

[B27]

anyone considered adding one of those air-water heat exchangers to an air heater, and running a matrix from that?

Might it be enough to heat the front of the boat, while the air does the back?

 

[Ceirwan]

I would not fit any fans, i'd put radiators in. I've worked on boats with matrices and they never seem to work particularly well.

I'll bench test one before I commit to fitting it, mads from sail life put a large computer fan on his in the forecabin IIRC, and apparently it was pretty much inaudible while still heating almost as well.
Its a sailing boat, so I don't have that much room for radiators apart from maybe a towel radiator in the heads.

Cheers for the headsup on Planar, I thought they only did air.

@mrangry those plinth heaters look quite good actually. about 0.4 amps and they reckon 1.4kw. That would do the forecabin.

 

[Refueler]

Its not diesel system ... its LPG fired hot water to radiators that are mounted along main cabin bunks. You can see the wood surrounds and just make out the radiator fins ...

The boat is 38ft ... as to what power the heater itself is - have no idea as its not in use.... supposed to have been disconnected by previous owner ... which TBH - I am having doubts. There's no gas ballon on board - so there's no risk at present.

Intention is to remove radiators / heater and replace with a Vevor Diesel fired air system. Hot water would be nice - but TBH .. not a big deal for me ..
We have considered trying the LPG system .. but we cannot find any manual for it ... (I have Gas Detectors ready to install !!)

 

[Ceirwan]

The boat is 38ft ... as to what power the heater itself is - have no idea as its not in use.... supposed to have been disconnected by previous owner ... which TBH - I am having doubts. There's no gas ballon on board - so there's no risk at present.

Intention is to remove radiators / heater and replace with a Vevor Diesel fired air system. Hot water would be nice - but TBH .. not a big deal for me ..
We have considered trying the LPG system .. but we cannot find any manual for it ... (I have Gas Detectors ready to install !!)

Hmm, those radiators would stick out like a sore thumb on my boat,, unless I can find a really good way to hide them, I'd probably need matrices in the saloon.
Ideally I'd stick with blown air as its what I already have, but its basically impossible to get the heating ducting past the aft end of the settee. The designer did very clever job of maximising all the space, but unfortunately that means that with water tanks & other stuff, there is room at most for a couple of water pipes to sneak past.

 

[Refueler]

Hmm, those radiators would stick out like a sore thumb on my boat,, unless I can find a really good way to hide them, I'd probably need matrices in the saloon.
Ideally I'd stick with blown air as its what I already have, but its basically impossible to get the heating ducting past the aft end of the settee. The designer did very clever job of maximising all the space, but unfortunately that means that with water tanks & other stuff, there is room at most for a couple of water pipes to sneak past.

You would think they detract from cabin space ... especially that the boat is 3m wide ... slim for her 38ft LOA ... but designed has been clever with internal space - so the cabin actually equals a 3.2m or more boat ..
Of course if you were ADD such to a boat - then you would 'feel' the small reduction

I thought about removing them - but then it would mean sanding / cleaning up the bunk wood to look good after so many years behind the radiators.

 

[stone beach]

I have some small domestic rads driven from a 5kw Eber Hydronic in a 38ft power boat. (Plus 2x matrices which I hardly ever turn on as they make too much noise and I wouldn't bother with them). Don't think it would be enough to be toasty in winter but it is plenty to be comfortable in Spring / Autumn UK. A simple electric fan heater gets all warm to kick off, without that it takes max 2 hours in cold weather.

Maybe you can hide a rad under a bunk or under a stairway? I have one boxed in with a manually controlled computer fan wafting over it, works fine. You could also put one in a hanging locker , its not like blocking off an electric heater it wont come to any harm, vent slots in the door, leave the door open to kick off.......

Forget about towel rails, use a small rad and leave the toilet door open.

Hydronic unit controls itself on water temp, I took the calorifier off the engine cooling system and put it into the heating circuit to provide some inertia, works fine.

I would pipe all the rads in series , no valves on any of them, using 3/4 heater hose and have a parallel loop for the calorifier with some simple gate valves to balance it out for summer and winter modes. If you need to fix something it is simple to drain the lot and refill, no valves = much less leakage points.

Domestic rads wont survive forever but they don't cost much from Screwfix etc, all in all it is quite a practical alternative.

If you are really going to use the boat in full winter then go up a size