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If I’m calculating correctly………. One of my rooms has two rads set against requirement of 2,668W. My plan was (reading off the DT50 75/65/20 degC Table) 2x 1,400W Type 22; 450(h) x 1,100(w) = 2,800W (I can’t go taller than 450mm). Factored for DT30; the I’d need the equivalent of 5,202W (reading...

Thank you @endecotp…….. The STELRAD data I’m looking at qualifies the T50 with ‘(75/65/20 deg C)’ . So the T50 is the delta of room temp at 20 deg C to the rad temp 70 deg C (being the mean of 75/65 flow & return). if I understand correctly - there is an opportunity here to make the boiler...

Thank you @Notch7 and @Mister Banks for reply. The boiler has (just) been replaced; ecoFIT pure 825 combi; 25 kW / 85,000 BTU. (Old boiler was Potterton 60e 18Kw). New boiler plumbed with two zones: - Z1 17sqm UFH installed and running now. - Z2 x9 rads; flow/return not yet connected -...

Thanks to advice gratefully received, I’ve generated my radiator shopping list (from U values / areas etc and no Apps). I wanted to check against rads that came out (sensible advice from @oldbuffer) that I’m in the right ball-park. I get the feeling the new rads are a tad larger capacity wise...

I’m in process of moving from vented to combi…… I’d like to put a new towel rail in the airing cupboard where the old HW cylinder was removed from. I’m pondering a low wattage electric element for when the boiler is on summer holiday. The alternative (grateful of thoughts); I have a...

Thanks reply. I was concerned that because it has a high thermal mass (big lump masonry), I would need to assume something like a 10 or even 21 deg temp differential. D

I’m working through my rooms; one by one. The internal wall of two rooms is largely made up of fireplace / double chimney breast. I’ve peered in from loft - it’s a single course of bricks with about 300mm of ‘in fill’ in the void between chimney. Would someone be kind enough to suggest a U...

Thank you for the advice…. - I’ve added a 10% weighting for intermittent heating - I’ve assigned different temperatures based on room type - I’ve included heat losses to adjacent internal rooms - I’ve identified solid / cavity walls (from advice on brick bonds) - I’ve dialled back the U value...

Thank you @endecotp - that’s an interesting idea. D

240mm measured at a Window. D

I’ve had a look at my brick bond on older (200mm) walls of house. The oldest part follows the bond pattern you describe: It then transitions to a newer (still old) bond of 2x long bricks followed by a half brick - would this be solid too ? Thanks D

Thank you @oldbuffer - that’s very helpful and generous of your time. As you suggested…… - I’ll add +10% for intermittent heating. - I’ll dial back the U value on the 1957 walls too. - I’ll have a look at the ‘brick bond’ on the older walls to see if I can get a better read out on the...

I’ve taken onboard the previous comments watched recommended video - thank you @oldbuffer / @Mister Banks. I’d be very appreciative if someone would be kind enough to take a look and confirm I’ve got things correct. Mindful of a previous observation …… I’ve assumed a U value (2.2) for a solid...

Thank you @oldbuffer & @Mister Banks. I will definitely watch recommended video when home. I’m pleased to read that I’m not far off mark. Q: Would you advocate this approach rather than an online tool; it wouldn’t be too difficult to apply this to each room. I did consider the internal walls...

I’ve been having some mixed results with the various on-line radiator sizing tools. Appreciate it’s not an exact science - but they seem a bit inconsistent and a leap of faith. So I thought I’d attempt a manual check to give me a bearing (or even use as an alternative if it works ok). I’d be...

For system context - brand new boiler; ecoFIT pure 825 combi; 25 kW / 85,000 BTU with two zones: - Z1 17sqm UFH / 16mm pipe under LVT (installed) - Z2 x9 rads all being replaced D

Having searched forum for ‘oversized radiator’ threads. There seems to be advice that oversizing of the entire (combi boiler) system can be beneficial. As I’m changing all my rads - I can do this / fit TRVs If I go through my BTU numbers (on-line tools) and err on side of caution……. - Assume...

I’ve since found that the 300mm high STELRADs I’m looking at, increase in length by big increments of 500mm. So I’m either a tad under spec or significantly over spec output wise. Noting earlier chat / advice - how much latitude do I have on being over spec. Thanks D

@endecotp - yes. By coincidence, I’m looking at STELRAD too. So that diagram very useful - thanks. 450+150=600 cill height, so I’m on limit. I might have to put wooden batten spacers behind brackets as the cill might make access to hang on bracket tricky (as I won’t have a gap). D

Thank you - sounds like 450mm should be okay under a 600mm cill. D