Garald

So, two narrow, tall radiators at about 500W, each close to one of the two ends of the long inside wall? And another one in the long corridor, since it will be used as library space (and so that it does not count as unheated space)? Does that sound best?

I've kept U=0.22 and reduced the wall space to 36.56 (since two of the walls are internal). I get 847W, which is really low. Even if I set the wall space to 48.30 (because a short wall adjoins the kitchen, which won't be insulated - doing so would require ripping it apart) I get a total heat loss of 916W.

(What scientists and math people say of engineers is that they do rather precise computations, with the necessarily imperfect data and models that they have, and then multiply everything by 2. I don't know whether this is an idealization or a slur.)

OK. But what is the margin of error here? Perhaps I should aim at a maximum of 1500W, to be safe?

Wait, is this an argument for or against overcalculating?

It's prudent to size it to -7 degrees (in that it's still fairly common, in that (I think) it happens most or nearly all years; no bougainvillias in Paris, though that may be changing). Anything less than -10 degrees is Eurostar-stopping, highway-closing. airport-disaster-movie weather. I certainly don't think I need to size the system for *less* than -10 degrees. If that ever happens again (not certain because of global warming), I can just use the chimney.

That's really not very much. That's one very tall radiator (a bit over 1000W at low temperature). Maybe I should put two radiators like that, on opposite sides of the long inside wall. Does that make sense?

OK, here's the outcome. So, what's the verdict? Surely not 868W? That's way too low. Heat loss calculator - Master (1).xls

And I should use 0 doors, simce there is only 1 door, leading to a corridor thst will probably be heated? What U value for the floor?

Ah, sorry, found them.

But I don't see any white cells for U or R.

LL? The (part-wooden) ceiling is below my (heated) attic, and the floor is mostly above a GP's (but his hours are short and he seems to be often on vacation), except for the part above my bikeshed (unheated, but will insulate the ceiling). 0 roof, 50% floor?

Do you mean the heat loss calculator? That seems designed for a house, not a room, and doesn't let me input U values.

Also, I guess this means I can take an old radiator that is now insufficient for the library or the main bathroom, say, and put it in a smaller space that needs to be heated (such as a WC), if there is room for it?

So, what power do I need to heat a 3.75x9.75m library to 20-21C when it's -7 C outside? (Assume it is well insulated: R of insulation at least 3.8, closer to 4.5 counting the brick wall and an air layer; I'm changing the double glazing, whose thermal perfornace is already high, by better double-glazing.) About 3 kW perhaps, so three of these radiators? Maybe put a fourth radiator in the broad corridor leading to it, since it will also be part of the library? (Put a cushy bench in front of that fourth radiator, especially for those who like to get toasted while reading?) (Anything significantly below -7C in Paris is basically Eurostar-stopping weather. If shove comes to push, well, you can see a working fireplace in the pictures.)

That would be a conversion factor of 0.2, not of 0.41, as given by https://www.clyderadiators.co.uk/delta-t-conversion , no?

Ah, it can't, says the architect - but it can fit in a closet in the entryway. In any event, I will have so much space in the garage, that, if my calculations are right, one will be able to fit a Citroën 2CV in it! That won't happen in practice, though - it will be a bike shed and storage space (since I do not have and cannot have a basement). But, who knows, perhaps a Microlino some day...

And I should compute at Delta 45-20 = 25 or so?

So, if I understand correctly, there's never any harm in leaving a radiator where it is; it's just that it may not be enough. So, say, if I have no use for the space under the window in the bathroom, I could in principle leave the little radiator there - I would just need a big, tall radiator elsewhere (maybe one from which I can hang towels). (OK, I wouldn't be literally "leaving it there" in that I have to move it to put in insulation; still, you get the idea.) Please confirm that I am getting the right idea. In general, I nee a bit more guidance, especially if I am to look at radiators that are not specifically labelled "low-temperature". Take this one: https://www.radiator-outlet.nl/eca-geribbelde-verticale-radiator-200x60-cm-wit-ra.html It would fit nicely between IKEA bookcases and it is within budget, even at the 60x200 size. But how should I interpret "3252 Watt", given that it does not specify a temperature at which that power is achieved? (Should I assume a default, and, if so, what default?) How much power do I need to heat a 9.30 x 3.85m well-insulated library to 20 or 21C on a frosty week (cold enough to mess with Eurostar, say: -5 C to -10C)? (And is that too long a space to be heated reasonably evenly with one radiator?) Where do I find models with blades? What brands have good quality/price ratios?

That makes sense - the ceiling separating half of the library from part of the attic is wood.

She's American, actually! The 200L tank isn't just cheaper - it can come in monobloc with the heatpump. Floor space gained counts for something, even in the bike shed.

Also, doesn't the architect's figure of 650eur per new radiator sound a bit excessive? Or is it about right? She said that the kind that could fit under the windows (not that that's a good idea...) would be much more (presumably because they are built with magic).

How do I measure the heat output of an existing radiator? Notice the ones under the windows are quite short (< 50cm) - these are large windows. Maybe the one in the entrance is large enough, and does not need to be moved?

... but we were thinking of putting reading nooks on the windowsills (see pictures): 20cm insulation + 25cm bookshelf depth = a nice, 45cm-deep reading nook. (We are putting 45 cm-deep panels on the sides of the bookshelves, to dissimulate the insulation.) Also notice that the library risks feeling a bit narrow, what with the insulation and bookshelves (we are taking care of using shallow bookcases), and double-depth bookshelves would compound that problem.

Interesting - I have seen them in La Casa del Libro in Madrid, but never for sale. (Links?) I wonder about cost - and mechanical wear. We'll have the bookshelves you see (but not the other ones) made to order in a factory, but at least they are competing with the price of ready-made bookshelves on sale everywhere.