Heat requirement per room - calculator

[RJEThorpe]

If you need to calculate what number and size of radiators you need for a room, this online calculator is really useful

http://www.theradiatorcompany.co.uk/heatoutput/

Found it while planning installation of GSH in old house. Just drop in room sizes and it tells you the BTUS and WATT requirement.

 

[MdB]

I would take those calculations as a very very rough guide only. They don't take into account the amount of insulation you have in the floors / walls / roof. In our house before renovation, the figures are about half what is required. In our house after the renovation, the figures are about double what is required. The difference being the amount of insulation we have put in.

 

[FamilyWiggs]

Some suggested variable factors quantified on this page:

http://www.castrads.co.uk/html/technical_data.htm

 

[chuckey]

Unless I am missing something, both these calculators neglect to neglect internal walls!, so the heat calculated is at about twice that which is necessary?.
Frank

 

[plumbers mate]

Don't forget toi count passages and corridors as the heat will migrate from your rooms into those spaces. The high half landing here is almost as big as a friend'sliving room stood on end so heating in that area has to be included a a room.

 

[plumbers mate]

plogies for typos as it's dark and I can't really see thekeuboard - the contents of each room are having to migrate to one side so the men can put central heating in starting next week... The bookks are all in one corner and the weight must be enormous - one floorboard has already "sprung " near the door....

 

[Lime]

In a great many houses it all hinges on the area of wall available to place a radiator.
While some larger houses have plenty of space but necessarily in the right place many other houses do not.
Then it is a case of buying the biggest radiator with the largest heat output to fit the space available.
The calculations for required heat output are meaningless when the radiator of "required" size does not fit in!

 

[Edwardia]

Neither of those websites mentioned something which we have found useful. Rooms with radiators under windows, (even double glazed windows) are colder than rooms with radiators positioned away from windows. I'm told that windows are sited under windows to equal heat loss ???? and also that windows are put under windows to maximise wallspace by the builders (more likely). So in our Edwardian house (which didn't have central heating originally) we have had modern "rads" with TRVs and "rad cabs" fitted away from windows so that we can have floor length lined curtains and cease heating the garden

 

[MdB]

The theory for putting rads under windows is that it sets up a convection current which gives an evenish heat throughout the room. With a radiator away from the window, the heat can go straight to the ceiling and stay there leaving it cold at floor level.

I've no idea if this it true or not in practice though.

(Underfloor heating should give an even heat throughout the room as long as you route and space the pipes correctly. Seems to work in our house.)

 

[plumbers mate]

A friend in a newly converted warehouse complains of the cold as all the heating is in the middle of the house - the half of each room which is away from the central walls is very cold. He has electric radiators to heat those parts of the room. It is a double glazed home too.

 

[Edwardia]

Heat rises, so I guess anything which forces the heat out into the room helps. Does anyone have any experience with ceiling fans ? Some reverse so would force warm air down ?

 

[ljn]

Putting radiators under windows does help the warm air circulate in the room. It also prevents condensation problems with the windows.

Radiators can perform well against a solid internal wall, as the thermal mass will store the heat and radiate it over time, but the room would probably be cold on the window side due to drafts and cold-bridging through the glass.

If you have wood panels and a well ventilated gap behind, a lot of heat could disappear.

 

[Craig]

I liked this one from Hudevad http://www.hudevad.dk/uk/cms/content/heatloss.asp

 

[plumbers mate]

Putting radiators under windows does help the warm air circulate in the room. It also prevents condensation problems with the windows.

Yipee - there's been a lot of that since the windows were draught proofed...

If you have wood panels and a well ventilated gap behind, a lot of heat could disappear.

Boo - below every window is a wooden panel with a gap and then brick between the rad and the outside world.

 

[ljn]

Booo, indeed! that's what I have too. Wood panel below every window a very draughty void and then a single course of bricks.

I don't know how big an issue is . There are people here who know about thermodynamics that could probably give a more informed opinion.

A sheet of reflective material placed behind the rad. http://doverprojects.blogspot.com/ would reflect the heat back into the room,
But there's no way I'm sticking that on georgian panels. I prefer wearing a hat and gloves.
Maybe there are more sophisticated ways of reflecting the heat. Putting insulation behind the panel (hoping not to mess up the ventilation of the building and cause damp or something)

I'm still putting the radiators below the windows. It still makes sense as the coldest part of the room, circulates the hot air and prevents condensation on the windows.

As Lime says, where the radiators go also depends also on the available space. Putting them in front of windows, avoids making new areas where you can't put furniture. When you count out the door, the windows, the fireplace and radiators, there might not be much free wall space for a bed, a wardrobe or a book case.

 

[Aidan]

They're usually below the windows because the glass cools the air; without the radiator you get a descending cold draught dropping down the window and flowing across the floor.

If you then put the radiator on the opposite internal wall, it generates an ascending warm draught and this accelerates the air current. The cold draught and discomfort that this arrangement can generate is extraordinary. It's much the same way that the gulf stream/atlantic conveyor works; high level warm ocean current goes north, deep level cold ocean current goes south.

It's less critical with good insulation and double glazing. Houses with solid ground floor often have the radiators on the internal walls.

Heat doesn't rise; warm air rises. Ceiling fans are useful with high ceilings; there have been several ducted systems marketed to shift warm high level air to low level. If the ceilings are high enough to give a measurable air temperature difference, it may be worth getting one.

Heat emitters work by both convection and radiation, and the proportion of heat emitted by convection affects the temperature gradient.