How many (low-temperature) radiators are enough?

[Garald]

[Preface: as quite a lot of people here know by now, I am doing a large renovation job on a place I bought in a near suburb of Paris earlier in the year. This is the last moment to make big decisions - work (demolition of some walls) should start this week. The place will be very well-insulated (for renovation standards) - 18cm cellulose on most walls, 11cm of cellulose+reflective insulation on the courtyard wall]

 

So,

(a) I am finally considering seriously installing a low-temperature heat pump, with low-temperature radiators, rather than simply switch over from a gas boiler to a HT heat pump. If I keep the number of radiators the same (14 radiators, for a place that will be about 120m^2 loi Carrez (= inhabitable area you can stand in, not counting staircases) and 180m^2 non-loi Carrez)), the net cost would be about 5800eur, including 800eur in increased work for the contractor and the architect. (Low-temperature heat-pumps are not just better, they are cheaper; however, low-temperature radiators are expensive - 650 eur a piece);

(b) a friend who advises me (N. the Philanthropic Flipper) was telling me: insist on having fewer radiators; the architect finds their number to be right, but N. says architects and contractors always overestimate the number of radiators needed, at least in the Paris area.

(c) the architect is a bit bothered by the possibility of a switch to low-temperature simply because low-temperature radiators are large, and we need wall space for bookshelves (I have about 1500 volumes currently, besides a vinyl collection, and the number of books seems to double every ten years)

 

In short: how many low-temperature radiators are likely to be enough?

 

It's a place with high ceilings on the ground floor and first floor (270cm to 290cm). Only the central part of the attic will be above 180cm.

 

Here are the plans (already showing the insulation and the work that will be done):

 

 

 

 

Presumably I want narrow, tall radiators, so as to use space efficiently (putting books right above a radiator is not necessarily a great idea in the long term, is it?). There are currently radiators under the windows, but it is very doubtful that low-temperature radiators will fit in there.

 

For a climate table for Paris, see https://en.wikipedia.org/wiki/Climate_of_Paris

Attention: the table there gives the average for 1991-2020. The climate is getting noticeably hotter in summer and milder in winter.

[Garald]

PS. Yes, I did do the heat-loss spreadsheet, but I must have input something wrong, as I am getting unrealistically small values. Here it is.

Heat loss calculator - Master (1).xls

[JohnMo]

Quick look.

Floor u value, looks low unless you have 200mm of insulation in the floor

Wall looks too low also based on their value you have talked about.

 

Wall area looks extremely low for a three storey building.

 

[Garald]

I agree I must have made a mistake. Let us try to find it.

20 minutes ago, JohnMo said:

 

Floor u value, looks low unless you have 200mm of insulation in the floor

 

I understood "floor area" to be "area of floor above the ground or unheated space". This is a roughly 8mx12m structure, so 76m^2 should be right.

(I will put some insulation on the ground-floor floor, but not that much - can't raise the floor by much without making incomers trip. The ceiling of the garage and of the co-op's corridor will be insulated, but the spreadsheet doesn't know that.)

 

20 minutes ago, JohnMo said:

Wall looks too low also based on their value you have talked about.

 

Let me see. First-floor inner walls: (12+8+12+8)*2.8 = 112m^2. Ground-floor walls: about (8+5+8+5)*3 = 78m^2 (the garage doesn't count). The attic has just the walls on the sides (the rest is ceiling), which are about 1.2m tall on average; hence (8+8)*1.2 = 19.2m^2. So, a total of about 210m^2, whereas I keyed in 200m^2. Let me put 220m^2.

 

The internal roof area should be sqrt(2.4^2 + 4^2)*12*2 = about 112m^2. Yes, that's what was much too low. New version attached.

 

The total volume should be closer to 500m^3 than to 400m^3.

 

Other than that: am I interpreting things correctly?

 

 

20 minutes ago, JohnMo said:

 

 

 

 

Heat loss calculator - Master (1).xls

Edited September 13, 2022 by Garald

[ReedRichards]

How old are the radiators you have now?  Do they have internal fins to increase the effective surface area?  Could you cope with "fat" radiators that protrude almost 20 cm off the wall?

 

I ask because some of my new "low temperature" radiators occupy less area than the old ones they replaced.  The old ones were were just double panel (c 1980) and my new ones are mostly double panel double fins with a couple of "fat" triple panel tripe convector types.

Edited September 13, 2022 by ReedRichards

[JohnMo]

All u values look too good.  Your min temp in Jan is only +3.2, so no frosts ever?

Edited September 13, 2022 by JohnMo
Missed word

[Garald]

Just now, JohnMo said:

All u values look too good.  Your min temp in Jan is only +3.2, so frosts ever?

There are years without snow. -5C is normal for a particularly cold winter night, but temperatures under -10C are a rarity - I'm not sure that has happened in the last 10 years. December 2009/January 2010 was cold (record: -13.3C, the Internet tells me).

[Garald]

23 minutes ago, ReedRichards said:

How old are the radiators you have now? 

 

Old, I take. Hopefully not from the 1930s, but old.

> Do they have internal fins to increase the effective surface area? 

 

Uh... see pictures.

 

 

 

(I'm not currently there - otherwise I could take close-ups.)

 

>Could you cope with "fat" radiators that protrude almost 20 cm off the wall?

 

Why not? Would fit nicely between bookshelves!

 

>I ask because some of my new "low temperature" radiators occupy less area than the old ones they replaced.  The old ones were were just double panel (c 1980) and my new >ones are mostly double panel double fins with a couple of "fat" triple panel tripe convector types.

 

Sounds like a good idea. The architect made it sound like low-temperature radiators that fit under my (low) window-sills would be extremely expensive - is that really the case? Of course they don't have to fit there - tall, fat and narrow would also be very good.

Edited September 13, 2022 by Garald

[Garald]

Tried to edit to show only a close-up, but for some reason I can't edit my previous post.

 

[MJNewton]

Having read a few of your threads (but evidently not one where you describe your place in detail!) I had this image in my mind of a dusty old farmhouse for some reason. Looks really nice!

 

(And on the topic of triple panel radiators you've effectively got them already dimensions wise so I think they'd be a good idea if required)

[SteamyTea]

You could look at plinth heaters (small, fan assisted radiators) for some areas, possibly kitchen, bathroom and hall ways.

If, depending on your layout, those areas are warmed in a controlled manner, you may be able to reduce the area/size of some other radiators.

Putting radiators under windows is a rather old fashion idea. Goes back to when windows leaked air and energy.

More normal to put them into internal walls now.

Radiators can be boxed in, though there is usually a hit in their performance. 

As you have a piano, and like to tinkle the ivories, how are you going to control temperature and humidity in the music room.

Our old family piano (from 1936) did not survive the introduction of central heating.

[Garald]

I think it started out as a very basic brick-and-masonry place in what was then (1930) the working-class outskirts (and still sort of is, though it would be "outskirts" only in the pedantic Parisian sense of being just outside the Périphérique - 10 min walking). Then successive owners have improved it, while neglecting to do anything about insulation, and leaving a gas heater that you run by sacrificing infants to Putin, a bit like in Salammbô. It's not every attractive on the outside - I'll do a bit of work so that it reaches "nicely inconspicuous" levels. Most of the ground floor is occupied by a GP.

>(And on the topic of triple panel radiators you've effectively got them already dimensions wise so I think they'd be a good idea if required)

 

You mean they are fat?

 

Here are some more pictures of existing radiators, with views of the greengrocer in front:

 

 

 

And here are our plans for what the library  (aka the one important room) will look like (though my girlfriend would prefer lighter wood):

 

 

 

Ignore the James-Bond-villain furniture, which was the architect's idea and won't become reality. (We'll put some of that money into good shutters and awnings instead, to avoid heat gain.) BTW, the architect is a bit anxious about losing wall space in the library. Maybe the radiators can be put on the lighter, IKEA-hack side that you don't see here.

 

 

At any rate, any help on how to choose new radiators for efficiency, size, shape, etc., and price are welcome, as is advice on whether 14 radiators is too many.

 

 

[Garald]

5 minutes ago, SteamyTea said:

Putting radiators under windows is a rather old fashion idea. Goes back to when windows leaked air and energy.

 

Right, I was wondering about that.

 

6 minutes ago, SteamyTea said:

As you have a piano, and like to tinkle the ivories, how are you going to control temperature and humidity in the music room.

Our old family piano (from 1936) did not survive the introduction of central heating.

 

Excellent question. My tiny Grotrian-Steinweg upright has a Dampp-Chaser system installed.

[SteamyTea]

6 minutes ago, Garald said:

And here are our plans for what the library  (aka the one important room) will look like (though my girlfriend would prefer lighter wood):

I am with her on that. Looks like my French relatives place.

Have you thought of double depth sliding bookshelves, get at least 50‰ more area.

Slide them across the windows and you get curtains.

 

I have a problem with books. If I have a shelf, I fill them.

Reality is that my Kindle is my main reading devise, so only really need to keep my favourite, sentimental value, ones.

I have a copy of Earth from the Air. It is terrific. But not opened it in 15 years.

[Garald]

24 minutes ago, SteamyTea said:

Have you thought of double depth sliding bookshelves, get at least 50‰ more area.

Slide them across the windows and you get curtains.

 

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.

[Garald]

... 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.

[SteamyTea]

1 hour ago, Garald said:

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.

Depends how wide the books are.

 

[ReedRichards]

Don't get it into your head that there is such a thing as a "low temperature radiator".  All you need is an ordinary radiator with a large surface area.  The radiators you already have probably have quite a high output (and some of the more modern styles would look wholly out of place in your apartment).  The one in your style that I Iooked-up appears to have an output of about 2 kW per square metre at delta T = 50 C which would be about 400 W per square metre at delta T = 25 C.  Maybe you can move some of your existing radiators around so you don't need a complete new set?  Or perhaps some of them are so over-specified that you can use the ones you have?     

[Garald]

41 minutes ago, ReedRichards said:

Don't get it into your head that there is such a thing as a "low temperature radiator".  All you need is an ordinary radiator with a large surface area.  The radiators you already have probably have quite a high output (and some of the more modern styles would look wholly out of place in your apartment).  The one in your style that I Iooked-up appears to have an output of about 2 kW per square metre at delta T = 50 C which would be about 400 W per square metre at delta T = 25 C.  Maybe you can move some of your existing radiators around so you don't need a complete new set?  Or perhaps some of them are so over-specified that you can use the ones you have?     

 

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?

 

[Garald]

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).

[Garald]

2 hours ago, ReedRichards said:

Don't get it into your head that there is such a thing as a "low temperature radiator".  All you need is an ordinary radiator with a large surface area.

 

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?

[SteamyTea]

Bit about radiators and temperature here.

I think most radiator output is at Delta 50.

 

https://www.clyderadiators.co.uk/delta-t-conversion

Edited September 13, 2022 by SteamyTea

[Garald]

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

[Garald]

4 hours ago, ReedRichards said:

The one in your style that I Iooked-up appears to have an output of about 2 kW per square metre at delta T = 50 C which would be about 400 W per square metre at delta T = 25 C. 

 

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?

[ReedRichards]

5 hours ago, Garald said:

Also, doesn't the architect's figure of 650eur per new radiator sound a bit excessive? Or is it about right?

 You can buy steel radiators much more cheaply than 650 euro but if you want them to be the same style as your existing radiators I don't know; I'm sure those will be more expensive. 

 

3 hours ago, Garald said:

 

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.

 

 Yes, that's exactly the right idea.  In my case I had a towel rail in my bathroom already but added an extra radiator to make the room warm enough.

 

3 hours ago, Garald said:

But how should I interpret "3252 Watt", given that it does not specify a temperature at which that power is achieved? (

 Yes it does.  You need to click to view the full specifications:

 

Quote

 

Vermogen 90/70/20°C

3252 Watt

Vermogen 75/65/20°C

2561 watt

 

That's 2561 Watts at delta T = 50 C and, as you correctly observe, 0.41 times this, 1050 Watts for delta T = 25 C (sorry about the error in my earlier comment). 

Edited September 13, 2022 by ReedRichards