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Engine bay heaters

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Just moved the boat from Broadsedge to Richos. Had to de-winterise so at least know the boat wintered well (so far). Having leccy hook-up at the new mooring I thought that rather than winterising again I would put a greenhouse heater in the engine bay of my Aquafibre 33. Most people seem to use a tube heater and if I use one of these what size would be ok - I have read somewhere that 80 watts is sufficient? That said, I do have a fan assisted greenhouse heater available and wonder if this would do the job?

Advice appreciated.

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I am happy to take the chance on shore power staying up as there seems to be a high degree of reliability at Richos. Also as we move towards spring the really bad cold nights "should" be a thing of the past (famous last words those ;) ). Also I only live 10 mins from the boat. If it were November I would cetainly do a full antifreeze job. So against all that - would a greenhousee fan heater serve as well as a tube heater?

Many thanks

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I have to say I'm not keen on non encapsulated heating elements in engine spaces and if the fan assisted heater is of that type then I would not like it in there. I'm certain it would do the job though, just that it would worry me a bit, unless of course it was a petrol engine in which case it would worry me a lot.

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I agree with Antaries, it's much safer to use encapsulated tube heaters.

My boat has got a petrol outdrive with raw water cooling, so I have to take a lot more care than most people. I understand that the recent cold snap has resulted in a great many cracked blocks in raw water cooled boats, even where people have relied on heating, where it has either tripped out or been of insufficient wattage for these extremes.

I've had an 85 watt tube heater in my engine bay for some time, but the max/min showed that over Christmas it still fell to -5c , so it wasn't sufficient this Winter.

I've therefore added a second one, controlled by the same thermostat, so I now have 170 watts.

As my boat is petrol, I have an electronic thermostat in the cabin, with a remote sensor in the engine bay, to remove the chance of any sparks.

I've also fitted brass drain cocks, so that I can also drain down the block and manifolds very quickly and easily. (and they were completely drained down during that last spell !)

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I have two tube heaters on dedicated frost stats set at 5c and I also close 75% of the engine air vents. I have an alarm that texts me if the power should fail and I can turn on the eberspacher remotely. Should I fail to do this the eberspacher will turn on at 2c regardless. Well you cant be to careful :lol:

Jonathan :Stinky

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Tube heaters and thermostat it is then. Next question, where is the best place to buy the kit? I am in the Potter Heigham are of Norfolk.


I scoured the Planet for the cheapest prices ( :naughty: ), and bought them via ebay for about £25, then found I could have got them from Wroxham at almost the same price !

http://www.norfolkmarine.co.uk/shop-onl ... -4597.html

The thermostat was somewhat trickier for me though, being a petrol boat I had to have a remote sensor elctronic stat, and that I could only find on the Internet for a reasonable price.

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Heater and thermostat duly obtained - from Norfolk Marine (B&Q did not have any in stock). Big question how do I wire the thermostat in? I have looked at the diagram but it seems odd - it is a shunt arrangement with Live, Neutral, Earth and Load connections. Load seems to be a continuation of Neutral but when the thermostat switches on it becomes Live. Presumably Load goes to the heater. I have done a lot of thio stuff so what am I missing :?

Diagram attached


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Live = live from mains, load = live to load (heater) that is to say the thermostat interupts the live feed from the mains until the contacts close at a pre set temperature.

It's a lot simpler just to buy a plug in "piggy back" thermostat that has a 13a outlet, but since you have already bought a hard wired one........

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I would have just run the live from the feed to terminal 3 and continues it from terminal 1 to the heater. I would have left Negative and Earth as direct feeds to the plug/power source.

From the wiring diag. that's what I would have read too and done precisely that, if you are in any doubt have it wierd up by a qualified electrician.

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That is what I thought Antares but what is that N wire? I would have just run the live from the feed to terminal 3 and continues it from terminal 1 to the heater. I would have left Negative and Earth as direct feeds to the plug/power source.

Those thermostats are a simple single pole on/off switch, so contacts 1 and 3 on the diagram act as the switch for the live feed to the heater.

So you connect the live incoming brown (live) wire to terminal 3, and the outgoing brown (live) wire to the heater to terminal 1.

You then connect BOTH blue "N" (Neutral) wires to terminal 4 and both green and yellow (earth) wires to the un-numbered earth terminal on the stat.

As Antaries has said though, if you feel at all confused about it, then it would be safest to leave it to an electrician.


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It does sound a bit extreme, but I don't doubt it.

I've seen a few outboard powered cruisers with an Eberspacher installed in the cockpit very close to the (plastic) petrol tank. :shocked

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