Radiator BTU and placement

[applecrumble]

Hi,

I'm replacing my whole central heating and boiler system as the current system is unreliable and inadequate. There's a lot to decide so was just wondering if anyone had any thoughts on my current plan.

Here's a sketch of the layout of my house where !!!! are windows and @@@@ is where I think I should put a radiator:

[code:1]
...|--!!!--|
...|..@@@..|
...|.......|
...|.lounge|
...|.......|
|---..|....|
|.....|....|
@.|-----..--
|.|..@|kitc|
|..wc.|hen.|
|.----------
|.|........|
|...bedroom|
|.|........|
@.|..@@@@..|
|.|--!!!!--|
[/code:1]

I'm going with double radiators under each window, two single radiators in the hallway (spreads the heat better than just one big one) and a towel warmer (just to get some heat into the bathroom). I've got single glazing at the moment but will probably get double glazing in the next few months. Does this radiator placement look OK? It seems to give a decent distribution of heat, maximises wall space and prevent cold window drafts.

Also, how accurate are these BTU calculators? Should I get, say, 20% above the BTU they suggest just in case? I was wondering if there are any efficiency concern if the radiators are too powerful.

Similarly, I'm not sure what capacity combi to get. I've seen some decent deals for 35C combis and they're only a little more expensive than some 25C combis. Is it worth getting one slightly more powerful just in case?

Any feedback greatly appreciated. Thanks!

 

[bengasman]

Radiators under windows is a rather outdated way of doing things, and also the least cost efficient. When you close the curtains early in winter when you need the most heat, the heat gets trapped. The rads will give you wonderfully warm windows, and either a cold room or an enormous gasbill.

Modern boilers work more efficiently with few large rads, than with many small rads. If you oversize the rads in the rooms, you can happily leave out the ones in halls and on landings, and will have a faster response time.

I have been doing it this way for a long time, and invariably my clients are very impressed with the results, and I have never had anybody complain about any room not being quite warm enough even in the coldest weather. But some people don't like the idea because we have always done it the other way.

 

[applecrumble]

Radiators under windows is a rather outdated way of doing things, and also the least cost efficient. When you close the curtains early in winter when you need the most heat, the heat gets trapped. The rads will give you wonderfully warm windows, and either a cold room or an enormous gasbill.

I don't have curtains at the moment. I could see the benefit in getting some heavy curtains but my house doesn't get that much light and I don't really have room for them. I wouldn't have the curtains covering radiators anyway. I was planning to get some shelves above the radiators and some blinds. The house isn't that big so radiators by the windows = more wall space.

Do you not agree with the reasoning that putting the radiators away from the window causes convention currents to form where cold air is pulled across the room? I find it hard to disagree with that.

Modern boilers work more efficiently with few large rads, than with many small rads. If you oversize the rads in the rooms, you can happily leave out the ones in halls and on landings, and will have a faster response time.

Any reason why they're more efficient when there are fewer and larger radiators? My partner likes the idea of having more radiators space to try clothes on; I think one radiator in the hallway is fine myself.

I have been doing it this way for a long time, and invariably my clients are very impressed with the results, and I have never had anybody complain about any room not being quite warm enough even in the coldest weather. But some people don't like the idea because we have always done it the other way.

One of my problems with this area is that everyone has different ideas about what's best but no hard figures. It would be nice if people could settle matters like this with some scientific tests. I will happily do whatever the evidence points to being best.

Thanks for your advice.

 

[bengasman]

Every house and every situation is different, so scientific tests go out the window. The next best thing is to find 10 people who have rads away from windows and ask them if they would like to move them back under the windows.
It is no good asking people if they would like to change to something new, sticking to the old, familiar way is common. The only people who can give an informed opinion are those that have had both ways.

If you and our girlfriend like small rads more than big rads, that is personal preference.

Rads in front of windows is not the most space efficient way either. The most space efficient is to stick them there where you are guaranteed not put any furniture in the future.

No, I don't think the theories about hot rads under cold windows cut any ice, and more importantly, my work has confirmed that. Theories and ideas are great, but nothing beats empirical data.

Drying clothes on rads is a very bad idea, makes the place cold and wet, and often causes mildew.

The how and why of radiator size and boiler efficiency has to do with the condensing aspect of boilers. To make a long story short, the lower the temperature of the water coming back to the boiler, the more efficient the boiler works. Small rads have a smaller temperature reduction in the real world.

What kind of heating do you have at the moment? Could well be that a smallish adjustment would give you years of comfort for little money.

 

[applecrumble]

Every house and every situation is different, so scientific tests go out the window. The next best thing is to find 10 people who have rads away from windows and ask them if they would like to move them back under the windows.

A properly conducted experiment is much more likely to lead you to the truth than 10 biased anecdotes. Physics works the same in all houses so if one radiator strategy was always best, you could easily show this in tests.

Rads in front of windows is not the most space efficient way either. The most space efficient is to stick them there where you are guaranteed not put any furniture in the future.

For the rooms we have, the window placement actually does seem to be space efficient for us coincidentally.

Drying clothes on rads is a very bad idea, makes the place cold and wet, and often causes mildew.

Agreed! I've bought a dehumidifier for drying clothes in winter.

The how and why of radiator size and boiler efficiency has to do with the condensing aspect of boilers. To make a long story short, the lower the temperature of the water coming back to the boiler, the more efficient the boiler works. Small rads have a smaller temperature reduction in the real world.

Ah, OK. I'll go read about this. I was just going either 1 radiator with a certain BTU or 2 rads that sum to same BTU. My thoughts on getting two was that one near the front door creates a heat barrier and also gives some more warmth to the bedroom.

What kind of heating do you have at the moment? Could well be that a smallish adjustment would give you years of comfort for little money.

I don't think what I have can be rescued. The boiler and pump needs repairs and the radiators all have rust! All rooms have single radiators with about half the recommended BTU; the bedroom one is tiny. The boiler is located in the corner of the bedroom. I was going to move the new one into a small wall cabinet to save space. The water tanks also take up a sizeable 1m x 1m cupboard so a combi would free up that space too e.g. I could make it into a shower room. The lounge and bedroom radiator placement also wastes wall space.

 

[bengasman]

A properly conducted experiment is much more likely to lead you to the truth than 10 biased anecdotes. Physics works the same in all houses so if one radiator strategy was always best, you could easily show this in tests.

You would have to find a sufficient number of houses, built exactly the same as yours, with the same heating use, same (lack of) insulation and draft, same boiler, and with half of them having rads under windows, and the other half not under windows.
Failing to find that option, you would have to conduct the experiment for all combinations of walls, floors, roofs, insulation, windows, sizes and proportions, and still have to make sure they have the same boiler, and same hours of on and off, and the same temperature per room.
Due to the human factor, it is not viable to conduct an experiment that comes anywhere near a qualification of scientific.

Even if you could, it would still have a big problem. Have you ever had a car that was really getting the mileage the book said it had? My car should do something like 11 miles on a litre of juice; I get about 8

 

[applecrumble]

You would have to find a sufficient number of houses, built exactly the same as yours, with the same heating use, same (lack of) insulation and draft, same boiler, and with half of them having rads under windows, and the other half not under windows.
Failing to find that option, you would have to conduct the experiment for all combinations of walls, floors, roofs, insulation, windows, sizes and proportions, and still have to make sure they have the same boiler, and same hours of on and off, and the same temperature per room.
Due to the human factor, it is not viable to conduct an experiment that comes anywhere near a qualification of scientific.

Researchers conduct successful studies into things much more complex that room heating all the time. With your reasoning above, all medical experiments, for example, are worthless in your view.

I'm confounded why you need to experiment with every single possible variable you've mentioned; surely if radiator placement is as significant as you say, radiators away from windows would consistently beat radiators under windows given the same test house. Simple repeat the experiment with different houses until you're convinced enough by the results. It's not that hard.

Even if you could, it would still have a big problem. Have you ever had a car that was really getting the mileage the book said it had? My car should do something like 11 miles on a litre of juice; I get about 8

The devil's in the details. You'd probably get 11 miles if you drove your car under the exact same ideal conditions in the experiment that was conducted. Either way, it's much more reliable than asking 10 car owners how many miles they get per litre (unless it was a controlled test and things were measured properly).