Good afternoon all, sorry if this seems like a stupid question but I am looking for advice. We recently had our bathroom done and were advised a Radox RXPS-1800400-CH would be man enough to heat the room. It isn’t, having done a bit of homework I think I’m going to go down the route of a convector radiator, the rest of the rads are convector rads. Is this the way forward?
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I'm not a plumber (well I DIY some) but I did design my heating system 
The best thing to do is look at the quoted output of the radiator or towel rail in watts. This will usually be quoted at a "delta T 50C" (delta may be written as the greek letter, a triangle).
So the bigger this number, the more heat you'll get out. Towel rails are poor - you'll be looking at 100-200W for a typical size. A finned single panel radiator of the same size will beat it by a significant factor.
My rule of thumb: if you have some idea how much heat it takes to keep the room warm, look for a radiator quoting 1.5 times as many watts at Delta-T 50C. If you want a cold room to heat up fast, add another 50% or more.
Cheers, Tim
Now - if you want to do actual calculations: (I apologise if this is egg-suckage, but if you're not aware)
"Delta-T 50C" means that when the average radiator temperature will be 50C above the room temperature, the heat output will be X watts.
No one designs to Delta-T 50C any more as the boiler will be running beyond its efficient point for a modern condensing type (where it wants the return to be less than about 55C - a little cooler is even safer/better)
A modern condensing boiler will more likely be running at roughly 60-flow/50-return or 65/55 at best, so your radiator temperature will be average of those, so 55C to 60C. If you're interested in heat output to maintain the room at 20C, that's a Delta-T or difference of 35C to 40C.
Delta-T 40C gives about 75% of the heat output compared to Delta-T 50C. Delta-T 35C is about 65% (some numbers I found online once).
So if you have some idea how much heat it takes to do the job, look for a radiator quoting 1.5 times as much at Delta-T 50C.
The best thing to do is look at the quoted output of the radiator or towel rail in watts. This will usually be quoted at a "delta T 50C" (delta may be written as the greek letter, a triangle).
So the bigger this number, the more heat you'll get out. Towel rails are poor - you'll be looking at 100-200W for a typical size. A finned single panel radiator of the same size will beat it by a significant factor.
My rule of thumb: if you have some idea how much heat it takes to keep the room warm, look for a radiator quoting 1.5 times as many watts at Delta-T 50C. If you want a cold room to heat up fast, add another 50% or more.
Cheers, Tim
Now - if you want to do actual calculations: (I apologise if this is egg-suckage, but if you're not aware)
"Delta-T 50C" means that when the average radiator temperature will be 50C above the room temperature, the heat output will be X watts.
No one designs to Delta-T 50C any more as the boiler will be running beyond its efficient point for a modern condensing type (where it wants the return to be less than about 55C - a little cooler is even safer/better)
A modern condensing boiler will more likely be running at roughly 60-flow/50-return or 65/55 at best, so your radiator temperature will be average of those, so 55C to 60C. If you're interested in heat output to maintain the room at 20C, that's a Delta-T or difference of 35C to 40C.
Delta-T 40C gives about 75% of the heat output compared to Delta-T 50C. Delta-T 35C is about 65% (some numbers I found online once).
So if you have some idea how much heat it takes to do the job, look for a radiator quoting 1.5 times as much at Delta-T 50C.
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Bain of my life these things , its a “ towel rail” not a radiator.
No one can really answer this without knowing heat loss and usage patterns for your bathroom.
600-800W (which is what your model seems to promise) should be enough to heat a typical medium-sized bathroom. Of course if you insulate it by covering it with towels it may struggle. I like one heated and one unheated towel rail in each bathroom for this reason. I also like heated towel rails to be dual fuel, on a CH loop that is not shut off by zone valves and controlled by a TRV. The electric heater is on a four-hour countdown timer that is just outside the door to help in the autumn/spring when the CH is not on for much of the time and the bathroom needs a boost. Use the heated rail to dry the towels after bathing but move them to the unheated rail so the rail can act as a heater.
3400mm X 2120mm, there are two external walls, one window and a tiled floor.
Yep. You can just about get away with a typical towel rail for heating with an tiny islanded bathroom right in the centre of the house like I have (and assuming the ceiling is warm or insulated, not onto a cold roof space). Anything else would be unlikely to work well unless you have other heating as well.
Edit: that's not to say you couldn't find a massive towel rail with a decent output of course - just thinking the typical type here...
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No chance pal , have you room for a rad and a towel rail?
at a pretty hot water flow temp (dT-50C/dT-60C) - if the OP runs his system at condensing temperatures, could be more like 400W
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As above if towels are going on it then you need a second rad / underfloor elec heating
If I was to get rid of the towel rail and replace it with a radiator would I be looking for a convector radiator as the rest of the ones in the house are or could I go for a a more contemporary designer? Bearing in mind I am looking for an 1800mm vertical by about 400-500.
We haven’t been putting any towels on it as it simply isn’t throwing enough heat out to warm the room.
I have a few of these: Ultraheat - Tilbrook - they have decent heat outputs for the size (one of the best I could find). There are other styles too from that manufacturer. Expensive mind...
Are all radiators convectors? If not, what are the benefits/drawbacks?
Yes - in that they *mostly* lose heat by convection. Technically they do radiate heat too, but this is relatively small amount (10-20%)
What BTU rating at T50 would you suggest?
W
Welder
Bain of my life too Town.
Some information. Chrome plated or polished stainless warmers put out less heat than white. These are not designed to heat the space. They, unsurprisingly, are designed to warm towels.
Just look at the difference in design of a radiator and a warmer. The surface area of a radiator is what makes it an effective heat source and that's orders of magnitude more than a warmer.
If you have a cold bathroom you will need suplementary heating in the form of underfloor heating or a proper (separate) radiator.
Some information. Chrome plated or polished stainless warmers put out less heat than white. These are not designed to heat the space. They, unsurprisingly, are designed to warm towels.
Just look at the difference in design of a radiator and a warmer. The surface area of a radiator is what makes it an effective heat source and that's orders of magnitude more than a warmer.
If you have a cold bathroom you will need suplementary heating in the form of underfloor heating or a proper (separate) radiator.
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Rob Foster
Esteemed
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There are combined towel rad and convector rad available
Rob Foster aka centralheatking
Sorry - don't do BTUs
But in watts...At a room size of 3x2m, 2 external walls (cavity with blown fibre insulation), double glazed, ground floor so warm ceiling, I reckon 1.5kW to 2kW of real power. So 1.5 times that for a dT-50C figure.
That's based on real life measurements (I used to heat my house with electric oil filled rads, so have a very good idea of power required).
Your mileage may vary depending on building type, insulation, windows and so on.
But with radiators, you cannot every have "too big" - so the biggest that you can get in the space is a good guide, without going completely OTT.
Beware, radiator outputs per unit area vary a lot. Double panel double finned are pretty decent. Triple panel tend to be humongous lumps.
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