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blackrose

Radiators for a Webasto thermotop C

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I have one of those reconditioned Webastos (5kW) that I'm going to install to an existing central heating system consisting of 4 x 800mm x 600mm single convector rads which I assume amount to about 10,000 btu or about 3kW in total +  a 60 litre calorifier. 

 

Should I change the 4 rads to double convector types which would total about 5.6 kW + the calorifier or leave it as it is before installing the heater?

 

Thanks

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I think you need to work these heaters hard for long life. For that reason, higher output rads are desirable and if you're gonna do it, now would be the time whilst the system is drained down anyway. Yours is a fat boat too, isn't it? So the extra output will be useful to warm you up more quickly. 

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So it's ok to overload the heater? If I change the rads to double convectors I'll probably end up with 8kW of rads & calorifier?

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3 hours ago, blackrose said:

So it's ok to overload the heater?

Yes, it’s best to overload them to stop them switching to low power. 

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5 hours ago, blackrose said:

So it's ok to overload the heater? If I change the rads to double convectors I'll probably end up with 8kW of rads & calorifier?

You don’t ‘overload’ the heater, you just over cool the circulating water which means the temp of the water going into the boiler will be a bit low, hence water temp coming out will therefore be on the cool side, the downside of this is the hot water in the calorifier will be a bit cool.  So you will need to fiddle with the rad valves to get the temps you want whilst not over restricting the flow and causing the boiler to cycle.

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2 hours ago, Chewbacka said:

You don’t ‘overload’ the heater, you just over cool the circulating water which means the temp of the water going into the boiler will be a bit low, hence water temp coming out will therefore be on the cool side, the downside of this is the hot water in the calorifier will be a bit cool.  So you will need to fiddle with the rad valves to get the temps you want whilst not over restricting the flow and causing the boiler to cycle.

Ok, if I leave the rads as they are I'll have about 3kW of rads +  a 60 litre calorifier. I'm not sure what that is in total, but with all the pipes I doubt it would be much under 5kW so wondering if it's better to leave it as it is rather than install bigger rads and then have to turn them down because the calorifier isn't getting hot?  

 

Or perhaps I should just change 2 or 3 of the rads to double convector which would give me about 4.3kW or 5.2kW of rads respectively + calorifier?

 

 

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6 minutes ago, blackrose said:

Ok, if I leave the rads as they are I'll have about 3kW of rads +  a 60 litre calorifier. I'm not sure what that is in total, but with all the pipes I doubt it would be much under 5kW so wondering if it's better to leave it as it is rather than install bigger rads and then have to turn them down because the calorifier isn't getting hot?  

 

Or perhaps I should just change 2 or 3 of the rads to double convector which would give me about 4.3kW or 5.2kW of rads respectively + calorifier?

 

 

I have one of those and run a large cauliflower, four double rads of different sizes, a dozen or so finrads and about 200 feet of 22 mil pipe. My rads get very hot and my system never cycles. This is all just for info I dont pretend to know all about heating :)

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5 minutes ago, mrsmelly said:

I have one of those and run a large cauliflower, four double rads of different sizes, a dozen or so finrads and about 200 feet of 22 mil pipe. My rads get very hot and my system never cycles. This is all just for info I dont pretend to know all about heating :)

Ok thanks, maybe changing all 4 rads is the way to go then.

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Remember when the calorifier is up to temperature it provides no load to the webasto, when mine is cold webasto runs flat out for an hour, when already hot webasto cycles down after 40 mins after it has heated the calorifier.

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I still haven't done this job but I have found more accurate figures for the radiator outputs.

 

My current single panel rads are about 821w each so about 3.28 kW in total.

The double panel/single convector rads I'm looking at are 1111w each so 4.4 kW in total.

Double panel/double convector rads are too deep and would be a major hassle to fit to the existing pipework so not an option.

 

So my question is, is it really worth changing the rads to double panel/single convector just for the additional 1.12 kW? Or should I change the 4 rads and also try to fit another small radiator somewhere to get the output even higher to match/exceed the 5 kW output of the heater?  

Edited by blackrose

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One other question: will the existing valves and fittings be ok for the new rads or do I need to buy new ones specifically for the new rads?

 

IMG_20200329_113334_104.jpg

IMG_20200329_113319_824.jpg

Edited by blackrose

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41 minutes ago, blackrose said:

One other question: will the existing valves and fittings be ok for the new rads or do I need to buy new ones specifically for the new rads?

 

IMG_20200329_113334_104.jpg

IMG_20200329_113319_824.jpg

 

In my experience making these boilers work hard is much better than the opposite - I don't like T/static valves on boats but don't really know why 

 

I agree with all that has been said so far - and I have been a user/ DIY installer - just re the aggro involved its far easier/better to do it now!!

 

BUT I'm not a heating engineer!

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39 minutes ago, blackrose said:

One other question: will the existing valves and fittings be ok for the new rads or do I need to buy new ones specifically for the new rads?

 

IMG_20200329_113334_104.jpg

IMG_20200329_113319_824.jpg

Given the known propensity of small pressure jet boilers to clog up if short cycled on high output I would change the rads, and add a new one if practicable.

The existing valves and fittings should be fine.  The radiator tails will also need to be changed over. I assume fitting  the webobasta will not change the direction of flow throuhh the rads.  If it does you will need to check the TRV's are OK with a different flow  direction. Most but not all are.

Don't forget to rebalance the system after the changes.  You may be able to do that at the TRV's, which makes taking one rad out for painting or whatever a bit  easier.

 

N

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Is there any point in TRVs on a system that should be flat out or off? Is there any point in rad valves at all? It can save drain down I suppose... I have none but my system is simple in that it has no cauliflower.

Edited by system 4-50

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27 minutes ago, BEngo said:

Given the known propensity of small pressure jet boilers to clog up if short cycled on high output I would change the rads, and add a new one if practicable.

The existing valves and fittings should be fine.  The radiator tails will also need to be changed over. I assume fitting  the webobasta will not change the direction of flow throuhh the rads.  If it does you will need to check the TRV's are OK with a different flow  direction. Most but not all are.

Don't forget to rebalance the system after the changes.  You may be able to do that at the TRV's, which makes taking one rad out for painting or whatever a bit  easier.

 

N

Thanks (and thanks to Halsey). I should be able to plumb flow and return in either direction at the boiler so that shouldn't be a problem. I'll just need to figure out which pipe is which in the engine room where the boiler will be located. I assume flow goes to the TRV? Why do I need to change the radiator tails? Can't I use the tails that come out of the existing rads?

 

These are the rads I'm getting. https://www.screwfix.com/p/kudox-premium-type-21-double-panel-plus-single-convector-radiator-600-x-800mm-white/98296 

6 minutes ago, system 4-50 said:

Is there any point in TRVs on a system that should be flat out or off? Is there any point in rad valves at all? It can save drain down I suppose... I have none but my system is simple in that it has no cauliflower.

So yours are plumbed straight in with 90 degree elbows into the radiator tails?

Edited by blackrose

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43 minutes ago, blackrose said:

So yours are plumbed straight in with 90 degree elbows into the radiator tails?

rad BSP straight to 15mm cu then 90degree rubber hose preformed bend from Car Builder Solutions (very expensive) down to 15mm cu to 22/15/22 cu Tee (Tectite Sprint (non-removable!!)) double pipe main, on both sides of the rad.  Tectite recommended by NMEA in an old post. Hoses for maximum flexibility since the main is 14M straight.  Can't get to the boat to take pics unfortunately.  Rads sized to fit local space ie smaller in bedroom.  Happy so far but not heavily tested.

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1 minute ago, system 4-50 said:

rad BSP straight to 15mm cu then 90degree rubber hose preformed bend from Car Builder Solutions (very expensive) down to 15mm cu to 22/15/22 cu Tee (Tectite Sprint (non-removable!!)) double pipe main, on both sides of the rad.  Tectite recommended by NMEA in an old post. Hoses for maximum flexibility since the main is 14M straight.  Can't get to the boat to take pics unfortunately.  Rads sized to fit local space ie smaller in bedroom.  Happy so far but not heavily tested.

Blimey, it sounds more complicated than just using a TRV!

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11 minutes ago, blackrose said:

Blimey, it sounds more complicated than just using a TRV!

I've used non valve solutions but with a push fit piped system and you can get rad fittings - some say balancing is important but you can achieve that with "hidden gate valves as I did and I never turned them down!. 

Edited by Halsey

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1 hour ago, blackrose said:

Thanks (and thanks to Halsey). I should be able to plumb flow and return in either direction at the boiler so that shouldn't be a problem. I'll just need to figure out which pipe is which in the engine room where the boiler will be located. I assume flow goes to the TRV? Why do I need to change the radiator tails? Can't I use the tails that come out of the existing rads?

When I said the tails needed to be changed over I meant take them out of the old rads and put them in the new🙂  People have been known to take the old rads out and ditch them ( to make space usually)  before removing the tails.....

The direction of flow is normally marked by an arrow on the side of the metal bit of the TRV.  Usually the flow is in through the TRV but if there are no markings you will have to consult the web to see what the makers says.

 

I don't think TRV are much of a benefit in a boat, though no experience of widebeams, but valves generally are the simplest connection solution and do allow you to take one rad out and still use the others.

N

 

 

 

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If you do have TRVs on all the rads then presumably you should have a PRV between the main flow and return pipes in case someone makes the mistake of shutting all the TRVs and then later switches the heater on without realising?

 

Two pipe radiator system

 

 

I think I'll just label mine "Do not leave shut"

Edited by blackrose

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I got my new rads yesterday which will total 4.4 kW. So I'm still under the 5 kW of the Webasto.

 

I was thinking of getting one of these for the bathroom as I can't fit anything taller, but it's expensive and a hassle to fit. It would give me approx 0.5 kW but is it really worth buying or will all the pipework and calorifier take care of the deficit?

 

Gallery

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23 minutes ago, blackrose said:

I got my new rads yesterday which will total 4.4 kW. So I'm still under the 5 kW of the Webasto.

 

I was thinking of getting one of these for the bathroom as I can't fit anything taller, but it's expensive and a hassle to fit. It would give me approx 0.5 kW but is it really worth buying or will all the pipework and calorifier take care of the deficit?

 

 

Yes.  By quite a long way.

 

Have you done the calculation for your pipework?  My pipework dumps more heat than the largest radiator does, admittedly by design (28mm copper pipe thermosyphon).

 

You need length of pipe, diameter of pipe, material of pipe and expected delta-T.

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Main 

1 hour ago, TheBiscuits said:

 

 

Have you done the calculation for your pipework?  My pipework dumps more heat than the largest radiator does, admittedly by design (28mm copper pipe thermosyphon).

 

You need length of pipe, diameter of pipe, material of pipe and expected delta-T.

The main run is about 26m flow and return all in 22mm plastic (uninsulated). 

 

delta-T? I guess the water temp will be 80C coming out of the boiler and ambient temperature is roughly... ambient!

Edited by blackrose

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3 hours ago, blackrose said:

Main 

The main run is about 26m flow and return all in 22mm plastic (uninsulated). 

 

delta-T? I guess the water temp will be 80C coming out of the boiler and ambient temperature is roughly... ambient!

I was told the Webasto evo throttles back about 75c, so I would use 72c as output, by which point the boat is probably becoming unpleasantly hot, say 25c giving a deltaT of 47.  But it is all a bit academic as you will have probably turned it off as the boat is hot and diesel is expensive. 

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