CH design and radiators...

[Tim Watts]

Is it correct to assume a radiator dT=40K for a modern condensing gas boiler?

70C flow, 50C return so average 60C , nominal room T=20C

Not sure about the flow/return temps...

[Tim Watts]

Oh - and what's the name of those radiator "shelves" that are curved underneath to flow air into the room?

Couple of locations that have to be under windows, it would be useful to stop half the hot air going the wrong side of the curtains...

Various google search terms have failed me:

radiator (heat) deflector radiator (heat) guide

radiator shelf is all conventional shelves...

[Andrew Gabriel]

I would make this the worse case. If you can size radiators for a smaller dT, even better still. Particularly worth considering with elderly people, where 60C can still burn without being felt in time in some cases (and todlers, but they will feel it).

Note that many radiator data sheets specify the power output at completely unrealistic dT (if you can even find it specified).

The system I put in can maintain the house temperature with a flow/return of 45/35 when just below freezing outside. I didn't actually intend it to be that good (was aiming slightly higher), but I'm pleased it is. It also means I can heat the house from cold very quickly by setting boiler to full power (it can't actually get the radiators to the max rated flow temperature of

82C, because their output exceeds the boiler's max output somewhere below 80C.)

[Tim Watts]

Good point. Thank you. I don not mind twiddling the boiler CH water stat a few times a year to balance it (manual compensation - the WBs do not seem to have a simple weather compensator without using their fancy controllers, which I do not want because I'll probably use an RF system).

I'm looking at the electric heating which is being monitored via ZWave in 4 rooms.

Each of 3 bedrooms (ground floor) and the kitchen/diner have 2kW per room electric oil rads right now (8kW total).

That is just enough to maintain the status quo at around zero outside like it is currently.

But if we return from a few days away, it is a struggle to heat the place from cold - I usually remotely turn all the heaters on about 6 hours in advance.

Kitchen is very space constrained because most of the walls are occupied

- prolly have to have 2 vertical rads, one at each end.

However, I found I can get a really long rad in the hall which will probably reduce the load on the kitchen rads as currently the kitchen heat comes back into the hall plus a lobby by the far rear door (2nd mini hall - that gets a small rad of its own).

Son's room can have a really long thin rad.

Daughter's room is a bit tight - our bedroom is typical.

Although I'm getting the CH fitted, I will be specifying the make/models of everything as it seems to be a little tricky to balance heat vs space limitations.

I noticed! dT=50K - what is this, steam?

Blimey that is amazingly good. dT=20C? Did you have lots of space for large surface area rads?

Which make of rad did you use? Best I can find so far are either Kudox or Stelrad and Kudox do a few in "33" (triple panel) format.

[Chris French]

In message , Tim Watts writes

I put in 3 Kudox rads last autumn.

I was happy with them. Seem well made and finished and well packed in cardboard boxes. Even the bracket fixings were decent (decent sized wall plugs and hex head screws

[Andrew Gabriel]

They are all Ultraheat. Compact 4 is their standard, and Compact 6 has two extra connections into the bottom of the radiator, which is useful if you don't want to lose space at the ends for the valves, and in the case of a triple panel, the TRV fits nicely under the radiator.

Triple panels are good for large rooms where you don't want to lose too much wall space - 4 of mine are triple panel Compact 6's. In one case it's because I could only get a 400mm high radiator under a recessed low window, the others are all in the larger rooms.

The choice of Ultraheat was because they were made just up the road, and a local independant plumbers merchant could get me any size within 3 hours. They had a crap website for years, but it looks slightly better now. I can't see the Compact 6's on it, but it never did have the full range in the past. Sometimes they supply a Compact 6 when you order a Compact 4, which just means you have 2 extra blanking plugs to fit.

These are both triple Compact 6's:

(Ignore the prices - I think I was charged about half list price including VAT, although VAT was less then.)

For singles and doubles, I have more recently used Selco (can't remember what the make is, but they all look very similar), but that was in a different location where I couldn't so easily get the Ultraheat's, and the Selco ones were probably cheaper.

[Tim Watts]

That rings a bell from a good while ago - thank you!

Interesting...

I was strongly considering triples for the areas that don't have a long bit of space. It seems that verticals are not *that* efficient and for some reason they have insane price tags.

Very smart - I see what you mean about the concealed TRV.

Brilliant - a handy reckoner for price.

Many many thanks Andrew - I am compiling a spreadsheet now...

[Andy Burns]

If my rooms were all at 20°C, I could live without central heating :-P

[Uncle Peter]

It's OCD to plan radiators. Just shove a radiator in each room where it's convenient to place it and see what happens. The boiler will come on more or less depending on what size you've selected and what the outside temperature is, you don't have to get it anywhere near correct.

[Andy Burns]

I bought several from Mr Central Heating last year, all doubles, some with double fin, others single fin. Delivered from their own vehicle rather than chucked about by some random courier.

Give them a look for prices ...

[Tim Watts]

Valid point - when we are at 20C we will only be balancing the heat loss.

Starting temp back from a holiday might be

[Tim Watts]

Thank you sir! - Bookmarked...

[Tim Watts]

They certainly seem to have almost every permutation of height, width and panel/fin count.

The efficiencies seem good too.

Unfortunately their website, which does actually list all the CF models and their data (in helpful units like watts and not "BTU" (BTU/h?) as one of their competitors does!) has just died mid way through my calcs.

#AnotherPHPWebsiteBitesTheDust

[Andrew Gabriel]

If you can get to mamufacturers rather than stockists, that is often the case. Hence, using a small plumbers merchant which didn't stock anything that didn't fit in a tiny shop unit, but could get anything in hours direct from the manufacturer, can be a good thing - much bigger choice.

It always was s**te, sadly. Might do better to phone and ask for a pricelist, which has all the details (and you could check if they still do the Compact 6's is they are of interest to you).

I've had mine installed for 13 years now. A couple of comments (which probably apply to all such radiators)... I haven't painted any of mine - I like the enamel finish, which has lasted fine on them all, except the one in the bathroom. This is starting to show some signs of rust along the bottom although not visible on the front, which I suspect is due to surface condensation during the summer when the room gets steamy during a shower. Might be an idea to paint a bathroom one, at least along the bottom. The second point applies to all makes in the last 20 years which have blanking plugs - the O-ring seals in blanking plugs don't seal for anything like as long as proper tapered plugs. Having said that, the Ultraheat are doing better than a B&Q and a Selco which are much newer, and the surface for the O-ring to seal against was rough as hell - I had to pack the thread with PTFE to make it seal there, which is not ideal as the O-ring plug thread is rather short and parallel, although it's working now. I much preferred tapered plugs, and I might replace the blanking plugs with nickel tapered plugs sometime (a bit more tricky for the one with the bleed valve).

[John Rumm]

A 20 ish degree drop is fair. The actual flow temp you would probably assume a maximum of 70 - 75 (the boiler will go higher, but you will lose much of the gains from the capture of the latent heat of vapourisation that is the whole raison d'etre of a condensing boiler)

[John Rumm]

IIRC, I used a few Kudox ones on my most recent rad juggling exercise. They seem equally well made as any of the better known brands, but were somewhat cheaper.

(note their figures specify the Tdelata as the difference between flow temperatur and ambient - rather than between flow and return)

[John Rumm]

Although if the heating is doing its job, that is the room temp (give or take a bit) they will be trying to maintain hopefully ;-)

[John Rumm]

You should be a plumber... or "heating engineer". You know, the kind of folks that explain why we DIY.

[Tim Watts]

Thanks John,

That's what I assumed - as deltaT-Flow/Return is only useful if you also know the flow rate, which noone does :)

I have been looking at my ZWave power measurements. Quite interesting...

To sustain at 20-21C with 2-3C outside, averager power over a day, no heating at night:

Our bedroom 1.5kW (contributes to hall, 2 outside walls, bay window) Daughter's bedroom - 400W (one short outside wall) Son's bedroom - 600W (2 outside walls, smaller windows) Kitchen 1.5kw (contributes to hall and rear lobby) - Also fire running in the kitchen, say 2kW more.

Total load about 6kW inc fire on an exceptionally cold day.

Conservatory - took a 2kW heater there plus power meter and temp sensor.

Started at 9C, 2kW flat out took it to 16C after 3 hours where it plateaued. Turned heater off - it fell like a stone, 13C in one hour.

So far I've managed to spec rads with a total output of 12.4kW at deltaT=30C (ambient 20C) so I guess 55/45C ?

At deltaT=40C the total output would be 17kW and according to your figures that is still running in condensing mode.

The conservatory would have UFH specced at about 2kW but in winter we'd use it just to keep the edge off the cold - say 12C and have a Myson fan convector for rapid boost - these seem rather good - their bigger wall model can shove out 3.8kW in Boost mode at deltaT=40C

Now, these are using the biggest radiators I can comfortably fit in - Kitchen is awkward as I only have 2 500mm long spaces, but triple panel rads seem to be better than verticals.

[Tim Watts]

Uncle Peter is being a wally.

CH installations is one of the biggest expenses so if you don't plan, you're a fool.

Although I'm subbing this out I don't trust any plumbers with the design so I'm specifying stuff :)