Plumbing Central heating radiator position

[Steve4Physics]

TL;DR Summary

Best position for central heating radiator

Hi.

The general advice for positioning a central heating radiator seems to be to mount it under a window. The reason being that windows are cold spots and the falling cooler air from the window and the rising warmer air from the radiator help the formation of a convection current around the room; this assists heating-up the room quickly and uniformly.

But surely this increases heat-losses - because the hottest air is nearest to the coldest region (the window and the external wall on which the radiator is mounted).

My instinct would be, if practical, to put the radiator on an internal wall opposite a window. There should still be a convection current created but losses through the window/external wall would be reduced.

Any views/experience with this?

 

[Lnewqban]

My instinct would be, if practical, to put the radiator on an internal wall opposite a window. There should still be a convection current created but losses through the window/external wall would be reduced.

The problem I see with that is that cold air leaking through the windows will travel horizontally along the rooms toward the heater.
That creates discomfort due to a cold draft.

 

[jrmichler]

An old technology uninsulated house with single pane windows has wall R-value about 2 to 3 and window R-value about 1.0. Those old single pane windows were poorly air sealed, and leaked a lot of cold air. The outside walls are cold, and the windows even colder. Positioning heating units under the windows where they directly counteract cold drafts is best for comfort.

My own house is insulated better than code minimum with R30 walls, R3 windows, and air sealed to 0.85 ACH50. I had the heating registers installed toward the middle of the house in order to minimize duct runs. There are no cold spots or cold drafts. The entire house is at an even temperature, even at -30 deg F outside with the wind blowing.

 

[Steve4Physics]

The problem I see with that is that cold air leaking through the windows will travel horizontally along the rooms toward the heater.
That creates discomfort due to a cold draft.

The windows are double-glazed which don't leak but would still be a source of colder air. So I think you are right - there is the potential for a cold draft along the floor unless the radiator is under a window

 

[Steve4Physics]

An old technology uninsulated house with single pane windows has wall R-value about 2 to 3 and window R-value about 1.0. Those old single pane windows were poorly air sealed, and leaked a lot of cold air. The outside walls are cold, and the windows even colder. Positioning heating units under the windows where they directly counteract cold drafts is best for comfort.

My own house is insulated better than code minimum with R30 walls, R3 windows, and air sealed to 0.85 ACH50. I had the heating registers installed toward the middle of the house in order to minimize duct runs. There are no cold spots or cold drafts. The entire house is at an even temperature, even at -30 deg F outside with the wind blowing.

Thanks. I've modern double glazed windows but the walls aren't well insulated (1880s brick house) so you have a great advantage! On the other hand, the temperature here (Devon, England) doesn't drop to -30^oF (-34^oC)!

 

[Lnewqban]

The windows are double-glazed which don't leak but would still be a source of colder air. So I think you are right - there is the potential for a cold draft along the floor unless the radiator is under a window

When wind is strongly blowing, or when mechanical exhaust induces negative pressure inside the house, undesired air draft from exterior envelope can still occur.

Please, see:
https://www.energy.gov/energysaver/detecting-air-leaks

https://garlandinsulating.com/2018/12/most-common-sources-for-air-leakage/

This is for Australia construction, but it has good points to consider:
https://www.yourhome.gov.au/passive-design/ventilation-airtightness

 

[Tom.G]

I had the heating registers installed toward the middle of the house in order to minimize duct runs. There are no cold spots or cold drafts.

Ahh, forced air heat, that makes a Big difference in placement options, especially in the colder climates and/or uninsulated walls & roof; not so much if it never gets down to freezing.

@Steve4Physics, it might be a good idea to consult an architect, or a good, well established heating contractor, . Also the local permitting authority may have some knowledge beyond the enforced requirements.

Your major heat loss will be thru an uninsulated ceiling. I highly recommend you get as much insulation on that as you can. While you are at it, see if there is acces to the space between the interior and exterior walls. If so, you can pour or blow insulation into the space.

Additionally, make sure there are no air leaks where the window frames meet the wall; caulk any gaps. An easy way to check for air leaks is with either a burning candle or some rolled up newspaper. Roll the newspaper tightly, set one end on fire, then blow out the flame. The newspaper will smolder for quite some time, emitting smoke so you can spot air leaks/movement. Of course it works best on a windy day.

Cheers,
Tom

 

[Ivan Nikiforov]

Radiators are installed under the windows also because it allows you to efficiently use the space in the room. If the radiator is installed on the wall in some other place, it will no longer be possible to install a wardrobe, bed or table in this place. Large furniture is not installed in front of the windows, so radiators are the best place there. You can recall the days when stove heating was used in houses and then, of course, there were no heaters under the windows. Therefore, the installation of radiators under the windows is most likely justified by the goal of creating a heat curtain in front of the window and saving space for furniture installation.