New radiators - totally baffled!

A1ps

This is a picture of the inside of the rad. To me it looks like a double panel, single fin (2:1).

A1ps

I'm going to be changing carpets so want to make sure I get it right first time, otherwise, if I need to change the piping at a later date because the rads are too small or too big, that'll be the death of me, and a possible prison sentence for me wife 

Albermarle

A1ps said:

FreeBear said:

A1ps said:

FreeBear said:

I'll often recommend the Stelrad heat loss calculator - It often suggests a higher rated radiator than many of the other sites you might come across. I had a recommendation for a ~900W radiator for my bedroom(s), but I fitted some rated at ~1350W at a flow temperature of 70°C (Delta T 50°C). This means I can run at a lower flow temperature and still heat the room effectively. This is important with a condensing boiler, as the lower the return temperature, the higher the efficiency. And having a low flow temperature means less work involved when a heat pump is fitted.

Suggestion - If the recommendation is for a 600x900 T21, go for a 600x1000 T21 - No real increase in price, but you get a little bit more heat out (just 150W or so). As long as you fit TRVs and balance the system properly, you won't increase the gas consumption. If anything, you'll be able to turn down the flow temperature and gain a little on efficiency. Even better if you can oversize all the radiators by 30-50%. But to get the best from low flow temperatures, you need decent size pipes. 22mm or even 28mm for flow & return, with short runs of 15mm to feed each radiator (micro-bore doesn't hack it).

I forgot to mention in my first post that I'm running a mega-flow for my water, and a system boiler for the heat.

@F@FreeBear , Stalrad calculations are stating I need a 2824 BTU (827w) radiator. Would going for a 4597 BTU (1347w) radiator be within the oversized suggestion you mentioned above? Or is that over kill?

The 600 x 900 radiator comes in 4137 (1212w). I'm wondering whether a larger rad by the extra 100 would make a difference?

How you generate hot water has no effect on central heating - The zone valves effectively make it two separate systems sharing the same heat source.

Going from an 827W  to a 1347W radiator is some 60% oversized. A bit over the top depending on flow temperature - A 600x700 T21 would be sufficient with a flow temp of 70°C.. With a flow temperature of 55°C, you need to be increasing the size of the radiator to get 827W out by about 63% (unless you had run the Stelrad calculator with a Delta T of 35°C).

Thank you. Would I then be better of sticking to a 600 x 900 which is 1212 watts and bTU 4137 (no need to move piping also)?

Likewise, stick to 600 x 900 for my loft room, which is 8m x 5m and has 2 rads either side of the room?

In your OP, you say you have a 20 m2 bedroom ( quite large for a bedroom) and the current 600 X 900 radiator is inadequate to heat the room properly. Now following all the varied comments, you are proposing to put in a new radiator of exactly the same size?
Just looking at the picture of the radiator under the window it looks smaller than 600 x 900. Are you sure it is that size ?

A1ps

Albermarle said:

A1ps said:

FreeBear said:

A1ps said:

FreeBear said:

I'll often recommend the Stelrad heat loss calculator - It often suggests a higher rated radiator than many of the other sites you might come across. I had a recommendation for a ~900W radiator for my bedroom(s), but I fitted some rated at ~1350W at a flow temperature of 70°C (Delta T 50°C). This means I can run at a lower flow temperature and still heat the room effectively. This is important with a condensing boiler, as the lower the return temperature, the higher the efficiency. And having a low flow temperature means less work involved when a heat pump is fitted.

Suggestion - If the recommendation is for a 600x900 T21, go for a 600x1000 T21 - No real increase in price, but you get a little bit more heat out (just 150W or so). As long as you fit TRVs and balance the system properly, you won't increase the gas consumption. If anything, you'll be able to turn down the flow temperature and gain a little on efficiency. Even better if you can oversize all the radiators by 30-50%. But to get the best from low flow temperatures, you need decent size pipes. 22mm or even 28mm for flow & return, with short runs of 15mm to feed each radiator (micro-bore doesn't hack it).

I forgot to mention in my first post that I'm running a mega-flow for my water, and a system boiler for the heat.

@F@FreeBear , Stalrad calculations are stating I need a 2824 BTU (827w) radiator. Would going for a 4597 BTU (1347w) radiator be within the oversized suggestion you mentioned above? Or is that over kill?

The 600 x 900 radiator comes in 4137 (1212w). I'm wondering whether a larger rad by the extra 100 would make a difference?

How you generate hot water has no effect on central heating - The zone valves effectively make it two separate systems sharing the same heat source.

Going from an 827W  to a 1347W radiator is some 60% oversized. A bit over the top depending on flow temperature - A 600x700 T21 would be sufficient with a flow temp of 70°C.. With a flow temperature of 55°C, you need to be increasing the size of the radiator to get 827W out by about 63% (unless you had run the Stelrad calculator with a Delta T of 35°C).

Thank you. Would I then be better of sticking to a 600 x 900 which is 1212 watts and bTU 4137 (no need to move piping also)?

Likewise, stick to 600 x 900 for my loft room, which is 8m x 5m and has 2 rads either side of the room?

In your OP, you say you have a 20 m2 bedroom ( quite large for a bedroom) and the current 600 X 900 radiator is inadequate to heat the room properly. Now following all the varied comments, you are proposing to put in a new radiator of exactly the same size?
Just looking at the picture of the radiator under the window it looks smaller than 600 x 900. Are you sure it is that size ?

Numbers have never been my thing. Failed maths at GCSE level - twice 

The bedroom is 5m x 4m. 

The loft room is 8m x 5m. That's where the confusion may lie. 

And the radiator is definitely D 600 x W 900 in the bedroom. And 600 x 900 x 2 in the loft room. 

The reason I was proposing the same size was simply due to one of the comments above stating the BTU figure for the larger rads might be too much of a jump from what the Stelrad website suggested.

Stelrad suggest 2824 BTU / 827W. Their 600 x 900 radiator figure is 4137 BTU / 1212W. That's why I thought this could be right. That's 1313 extra BTU. And 385 more watts.

The other guys have also suggested going larger. If so, I'd go up to 600 x 1000, which would give a output of 4597 BTU / 1347W. That's 1773 extra BTU. And 520 more watts.

I really am so confused. So sorry if I'm being really silly here. 

FreeBear

A1ps said: The reason I was proposing the same size was simply due to one of the comments above stating the BTU figure for the larger rads might be too much of a jump from what the Stelrad website suggested.

Don't forget that as you drop the flow temperature, the actual heat output from the radiator also decreases. When shopping for radiators, the heat output is normally based on a ΔT 50°C (or a flow temperature of 70°C). Turning the flow temperature down means you need to fit larger radiators to compensate if you want to maintain the time it takes to heat the space. This page gives a bit more info - https://www.clyderadiators.co.uk/delta-t-conversion

The alternative to increasing the size of the radiators is to either turn up the flow temperature (and burn more gas) or reduce the heat loss by insulating, insulating, and then insulating some more.

You've already said several times that the rooms are cold - The simple and least costly solution is to install larger radiators. If you go to someone like City Plumbing, they may well be able to reduce the price if you are buying several radiators of the same size (they'll also do free delivery). One reason i went for 600x1000 rads was 'cos I got a reduced price (and free delivery)

ThisIsWeird

A1ps said:

This is a picture of the inside of the rad. To me it looks like a double panel, single fin (2:1).

Yes, commonly referred to as a 'Type 21'. '2' = panels, and '1' = fins.

That type and size on SF https://www.screwfix.com/p/flomasta-type-21-double-panel-plus-single-convector-radiator-600mm-x-900mm-white-4104btu/559xp says it outputs around 4,100 btu, or 1200 watts.

I'm going to use tried and tested scientific principles to determine the best size you should go for. That wee rad looks very silly under your window, so I'd go for one that goes pretty much the whole window width. Sorted.

Say, 1600x600 - https://www.screwfix.com/p/flomasta-type-21-double-panel-plus-single-convector-radiator-600mm-x-1600mm-white-7295btu/648tg Yes, it costs a lot more, but there's no way around this - your current rad is not outputting enough. So you either live with a cool room, or you upsize.

That 1600mm jobbie has a 7200btu or 2.1kW output. That should, I think, be enough to warm that room easily with your current water supply temp, and 'adequately' with a lowered water temp.

If it turns out it's too powerful - ie it heats up that bedroom faster than other rooms heat up - you just turn the lockshield down to make it a 'smaller' radiator - one that heats up more slowly, and releases less heat. You can even make that 1600mm rad the same 'size' as your current 900mm rad if you want to.

You can do room calculations until the cows come home, and you'll likely end up in the same ballpark. I often use the 'electric heater' method personally; if I need to choose a water rad size, I ask myself, "What size of electric heater would heat this room? One bar? Two? More? So, how many 'bars' will your bedroom need?! If the answer is more than two, then even that 1600mm jobbie ain't big enough, so go larger!

On a different note, that boiler you mentioned is coming up as a 'combi' type and not 'system', but you say you have a hot water cylinder? When you run a hot tap, does your boiler fire up?

Either way, it's a beast, and has plenty of output.

Albermarle

I'm going to use tried and tested scientific principles to determine the best size you should go for. That wee rad looks very silly under your window, so I'd go for one that goes pretty much the whole window width. Sorted.

Say, 1600x600 - https://www.screwfix.com/p/flomasta-type-21-double-panel-plus-single-convector-radiator-600mm-x-1600mm-white-7295btu/648tg Yes, it costs a lot more, but there's no way around this - your current rad is not outputting enough. So you either live with a cool room, or you upsize.

Our loft room has 20m2 usable space ( about 25 m2 overall) and has a radiator approx the size you suggest. It heats the room up OK. Probably would be OK with something a little smaller as the room is well insulated, but for the OP it seems like a safe suggestion.

FreeBear

ThisIsWeird said: I'm going to use tried and tested scientific principles to determine the best size you should go for. That wee rad looks very silly under your window, so I'd go for one that goes pretty much the whole window width. Sorted.

Say, 1600x600 - https://www.screwfix.com/p/flomasta-type-21-double-panel-plus-single-convector-radiator-600mm-x-1600mm-white-7295btu/648tg Yes, it costs a lot more, but there's no way around this - your current rad is not outputting enough. So you either live with a cool room, or you upsize.

That 1600mm jobbie has a 7200btu or 2.1kW output. That should, I think, be enough to warm that room easily with your current water supply temp, and 'adequately' with a lowered water temp.

Don't forget, with a flow temperature of 55°C (ΔT 35°C), output of a 600x1600 radiator is going to be ~1350W. There is also a big jump in price when you go above 1200mm (just in case there are any budgetary constraints).

A1ps

Thanks guys again for absolutely invaluable information and help. I sincerely appreciate it. 

I just checked my flow temperature on the boiler - it is in fact 65 degrees NOT 55 as I guessed before.

@ThisIsWeird thanks for the link. I'm going to measure the window width tonight to make sure this size fits the width. If not, will look at ones that do fit. 

Are there any negatives for going for FloMasta over the Stelrad? Price isn't an issue as I want to make sure I get it right first time round, regardless of cost.

@Albermarle would you mind me asking the width and depth of your loft room please? I want to make sure I get the correct rads for that room too, and for the kids and mum's room, and the hallway. 

Can I be cheeky please, and ask for recommendations on these rooms too please?

Kids room - W 4 x L 3 x H 2.3 Window Area 2.4m2 Radiator would have to be 600 x 900 due to space

Mum's room - W 4 x L 2 x H 2.3 Window Area 2.4m2 Radiator would have to be 600 x 600 due to space

Loft - W 8 x L 5 x H 2.3 Window Area 2 m2

Hallway - W 6.2 x L 2 x H 2.3 Window Area No windows  Radiator would have to be 600 x 900 due to space

A massive thanks again 

BarelySentientAI

Some people say that Flomasta are lower quality and more prone to springing leaks.

Then again, you will always find some bad reviews of any product.