Can you include the heat loss from the plant in the calculations, as these may help you meet the heat loss for the room? A DHW tank can lose (emit) 100W per hour, and a volumiser 50W, not to mention uninsulated pipework.

Posted by: @adamk

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having a big renovation of the house so getting a heat pump in at the same time, but ive got a problem room. weve created a new bath/util room with a dedicated plant room within it for the HW tank etc. the ceiling is insulated the floor is insulated the walls on both sides are insulated. the other 2 walls are thermal type blocks. whole room is dot and dabbed. tiny double glazed window 400x800. heat loss for the whole area is 593W for just the actual area that is the bath/util its about 492W. im struggling to find a stainless steel towel rad that will fit in the 550Wx2300H wall that can manage much more than 250W at the 40c design flow. dont want to use underfloor and floors tiled now anyway. dont want to use normal rads if possible as they tend to rust. the main flow and return 28mm's to the house are running in the ceiling void so might help with some heat into the room?

ideas?

I persuaded my installer that heat loss from the adjacent hallway plus steam when you actually take a bath/shower was sufficient (in order that we didn't have to replace an existing towel rail).  In practice its true!

@adamk  I'm sure I recently answered a similar question but here you go:Nordic Omega Aluminium

This is what I put in my bathroom to give me high output at low flow temperature in a small space and it had to look good. 

I took a punt on it initially and it has very much exceeded my expectations. The finish absolutely shrugs off any moisture in the air, the technical design is unlike anything I've ever seen with vertical convection fins and it packs out the heat. They come in multiple sizes. 

If you are not in a hurry they will produce almost any RAL colour finish that you want. 

Posted by: @lucia

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@adamk  I'm sure I recently answered a similar question but here you go:Nordic Omega Aluminium

This is what I put in my bathroom to give me high output at low flow temperature in a small space and it had to look good. 

I took a punt on it initially and it has very much exceeded my expectations. The finish absolutely shrugs off any moisture in the air, the technical design is unlike anything I've ever seen with vertical convection fins and it packs out the heat. They come in multiple sizes. 

If you are not in a hurry they will produce almost any RAL colour finish that you want. 

what about galvanic corrosion as i have copper pipes and other steel rads.

@adamk Truthfully, I'd never heard of such things. Google (from sensible sources) says there needs to be an electrical contact with both metals. Not in my bathroom, thanks. 🙂

Seriously, Aluminium is highly rated for radiators and 100% recyclable. They're also a joy to hang because of being much lighter than steel. I'm very pleased with mine. 

Posted by: @lucia

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Google (from sensible sources) says there needs to be an electrical contact with both metals.   No in my bathroom, thanks. 🙂

Except that water is a conductor. 

Galvanic corrosion is a well known process problem with steel narrowboats, with the conductor being the  water, so I wouldn't rule it out.

@jamespa What I know about radiators you could write on the back of a postage stamp. And most of that you guys taught me when I was buying a heat pump. 😁

But isn't corrosion the reason why we put inhibitor in radiators? Certainly my plumbers do. Whatever they're made of.

The radiator I linked to is a beautifully (Italian) made piece of metal with a 15 year guarantee. I'm fine with that. My last lot of rads lasted about 40 years (although to be fair, they weren't ally)

I'll save my stress for Gaza and madmen with nukes in the Whitehouse.  However, if all else fails, the scrap value of Aluminium is pretty good and pretty constant. 😉

Posted by: @lucia

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But isn't corrosion the reason why we put inhibitor in radiators? Certainly my plumbers do. Whatever they're made of.

Yes it is.  

Steel narrowboats have zinc anodes for the same reason, but the steel still rusts, just less slowly.  

I have not personally heard of galvanic corrosion being a problem in central heating systems nor have I seen warnings from radiator manufacturers about mixing materials so I'm guessing it's not actually much of a risk.  It might be worth asking the question though to see what the reaction is.

@jamespa I see that boats in saltwater are now being suggested to use aluminium anodes which I believe also work in fresh water, whereas zinc is passivated in fresh water.  Don't some hot water tanks have an anode? Thankfully we don't use seawater in our heating systems! 😀