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I'm thinking about repositioning the heating vent from the front wall of the windows sill to the top of the sill. Under the sill, I have hot water radiators to provide the heat.

How will this affect the heating flow and the overall room temperature?

Should I expect less, the same amount or even a better flow since the flow may be going more directly into the room?

heating comes from the front of windows sills wall example of heating from the top of windows sills wall TO-BE scenario

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  • Have you remove any vents to see what's behind there? With what's blocking them noe, I have to believe you'd have better flow from the top. – JACK Jul 17 '20 at 1:55
  • A better explanation of the whole project is needed to give an accurate answer to your question such as what type of heating do you have at the present time. ( air, steam or hot water, and is it forced or convected). Is this a home or a business? How large is the space? What will the space be used for? – d.george Jul 17 '20 at 11:10
  • More details: the heat is generated by a heating radiator. hot water pipes are connected to the radiator. This is a home project (living room). The room is 13 ft x 19 ft. I removed the vents at some point: the radiator is close to the floor, as wide as the vents. There is an internal metal cabinet/duct that lead the heat to the vents. The top of the window sill is also metal, however it is not the top of the metal duct. The duct top is ~2 inches lower than the sill top (in line with the opening of the vent). – Fabrizio Jul 17 '20 at 14:16
  • @Fabrizio I've edited your hot water radiator information into the post itself. That's really the way to do it - not everyone reads all the comments, so things can get lost down here. Additionally, comments are sometimes deleted by a moderator when there are a lot of them and this info could end up getting permanently lost. Please take the tour and browse the help center to learn more about how things work around here. – FreeMan Jul 17 '20 at 15:03
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You only use heating when it is cold. When it is cold, the windows will be cold. Running the heat up along the cold windows will allow the windows to suck the heat out of the heated air and to the outside. As you have it now, the air is being pushed out into the room to circulate and mix with the other room air, warming the space, not the windows. Eventually the warm air gets back to the windows and gets chilled against them, but it is not circulating as fast. Doing what you propose will likely accelerate that process. I would not do it, your heating bills will likely go up.

What is your reasoning behind this?

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  • Thanks JRaef, the project is mostly to improve the aesthetic but also I was wondering if it could bring energy benefits. – Fabrizio Jul 17 '20 at 14:21
  • I can't say I agree with this. In my cold state, floor vents are often placed below windows to reduce frost and condensation and improve comfort. – isherwood Jul 17 '20 at 14:56
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It use to be necessary to have vents in the top of heating units and have those heating units located under windows when the heating units were hot water or steam units and heated rooms through convection. Condensation was very important to control because most windows were single pane and “sweat” a lot.

Now with thermal pane windows and forced air units, the location of the heating unit (or in your case the direction of the grille) is not so important, because air is pushed around the room and does not rely on convection for heating. (Often heating air grilles are located in the ceiling.)

We now size heating units based on the number of air changes required per hour. Mixing air creates a more uniform temperature throughout the room...no “hot spots”.

Changing the direction of the grille will not significantly make the heating unit more or less efficient. However, modifying the heating unit to discharge upwards rather than horizontally can effective the efficiency of the unit and possibly void the warranty.

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