Radiators under windows

[madnessIsay]

Me again, as part of redecorating Im going to replace one radiator (on the wall). There is another short long radiator that runs under the windows that’s ugly. Do I replace or just remove. It it draughty if you sit near the windows (big sash ones - single glazed) but I have shutters & was debating about curtains.

I want to know about this too. We have a long living room with a window and radiator under it at each end so the curtains only cover the window, not go to the floor so don't look very nice.

I was thinking about moving the radiators and getting floor length curtains but not sure where to put the radiators.

But I do know that radiators come in BTU sizes and you can find calculators on the internet where if you put in your room size, it will tell you what BTU of radiator(s) you need.

I read somewhere that underneath a window is the most effective place for a radiator, not sure why. We have blinds not curtains so don't have this problem however in our old house I used to tuck the curtains behind the radiator 😂 Not the most Instagram worthy living room to be fair.

I think that radiators should be placed under windows in older houses with single glazed windows. Something to do with the heat from the radiator rising and creating a more even flow of temperature throughout the room. Less important in newer super insulated houses. I can't explain the physics though.

yes i’ve heard they should be by radiators but was unsure if I had to do it if I had a super high BTU radiator in the room & installed. curtains.

by windows!

I'm a HVAC engineer so can give you some tips.

Radiators are meant to be placed in the coldest point of the room. Historically that would be under a window or on an outside wall. However thanks to double glazing and modern built homes having better thermal performance associated with better building materials there is sometimes no cold spot. This is good because it then means you can place the radiator on any wall you like.

You next need to determine the heat load necessary to heat the total room and then convert that to BTU. You are correct about the internet having lots of helpful calculators. If you can't find one I can let you know how to do it manually (it's very simple!).

If you find a radiator that can meet the duty of the BTU you require and it's dimensions fit in the space you have available then you can do away with the one under the window that you don't like and just have the new one. You may find the window draft gets worse with it gone though so you will need curtains or similar to help minimise it. Or you may find you need one radiator so big that having two smaller sizes to make up the duty would look nicer. The bigger the heat load/ BTU requirement the bigger the radiator (typically).

Also consider where your new pipework will need to go if you do put a radiator in a new location.

With any radiator don't cover it up as it can't function properly and therefore won't heat your room. Essentially if hot air can't rise away from it it also can't drag cooler air into the bottom of it to create necessary air movement.

Sorry for the long post!

thank you Annajohnsdottir much appreciated! Can I ask your view on vertical radiators as I was going to replace the one currently behind the door with one of these. Same footprint but I can get higher BTUs.

I would appreciate your calculation too please.

Even with the radiator under the windows on, it’s pretty draughty so I think curtains are a necessity. It’s only because I have a chair by the window, if you sit in the other sofas it’s fine.

You're welcome OP!

I think vertical radiators are great and they perform just as well as conventional radiators. I put one in my living room extension and it out performs my existing, old school radiator at the other end of the room. I will get around to replacing that one day too! They've come about to make the most of vertical wall space and also add to the overall aesthetic of a room. They're normally constructed in basically the same way as a horizontal one so perform the same as long as you haven't undersized it for your room.

Just so I give you the correct figures, what kind of room is the radiator going in please? Is it a living room or similar?

👍🏼 for vertical radiators. Yep living room with high ceilings (georgian property).

Under windows and tuck curtains behind them (for warmest and most efficient, not necessarily most stylish!)

To calculate BTU you take the area of your room (in metres) and multiply that by a set value to factor in double or single glazed windows and doors.

Room Width x Length x Height x 135 = the BTU total for a living room with a single glazed window.

E.g. 2.5m wide x 4m long x 2.4m high x 135 (single glazed living room value) = 3240 BTU. So you would require 1 radiator with at least this output to heat the whole room.

The set value changes by room because different rooms are recommended to reach different temperature to be comfortable to occupy.

One thing to note is there is no industry standard for calculating this and it's all done by rule of thumb. So you may find a slight variance between different calculators if you use them for comparison. The bottom line is never go below the minimum BTU and everything should be fine.

Thank you!

Sorry one last thing. Try to avoid placing a radiator opposite your drafty window. It will create a thermal circulation that will eventually stabilise so that the top of the room is warm and the bottom is cold, but while it is stabilising the air movement also creates a draught. Not pleasant!

I didn’t know that, but it’s going on the left side.

I’ve just read all this with interest despite my house having a slightly odd design and all the windows (bar the bathrooms) go all the way to the floor! (Stupid design in bedrooms if you ask me)

I did think under the window was the worst place so it’s been interesting learning about the physics of it all. Everyday a school day!

We also have a Georgian property. In our sitting room, the radiators are under the windows but I have full length curtains in there; I just shut the shutters at night and never pull the curtains which works fine.

In other rooms - depending on size, use, etc - I've removed one of the two useless single radiators and replaced with a Type 22 in a suitable position which keeps us comfortable.