My home has a hydronic heating system, with fully enclosed floor radiators. In one room, there is a radiator that runs the length of the room, on the outside wall which is about 20' long. In the center of this run, I want to install a set of french doors to the outside. In order to do so, I will have to have about 7 feet of that run diverted into the floor. So it will run down the wall, dive down into the floor on one side of the door, and then pop back up on the other side and continue on as it was.

Will losing this amount of radiator have a significant impact on its ability to heat the room in winter? This is Ohio and it's a west facing wall (windward side).

Some additional information, from comments:

  • this is a hydronic baseboard setup, with louvers on them that can be closed to minimize the convection and thereby limit the amount of heating.
  • the space where the door will go is already occupied by a window of greater width, but lesser height. In essence, this will replace one set of glass for another.

Maybe I am missing something here but the entire loop will still be in the room so there will be heat in the wall And the floor with a longer loop. but my concern would be air trapped in this loop could kill the loop if you don’t have flow restrictors on your manifold.

  • Interesting point, Ed. Could you elaborate on the flow restrictive part? I doubt there is, but I also don’t know exactly what to look for either. – DonBoitnott Jul 1 '20 at 23:28
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    Don on hydronic loops that I have installed there may be a dozen different paths back to the boiler. Some are thermostatically controlled valves some by flow restrictors and or a combination. For example in a large room there were 3 loops 1 manifold that was controlled by 1 temp valve. 1 zone of the room was constantly going cold if we put flow control on the loops we could restrict the other 2 loops and that loop quit air locking. Even though there was a DA tank and this was a low pressure/ open system several loops possibly had high spots and would air lock adding flow and temp valves fixed – Ed Beal Jul 2 '20 at 13:26


That room will become one-third less comfortable.

Hydronic heating works best when installed near a cold/draft source such as a window so that the cold air falls into the heater and gets released back out as warm air; this is why it is on your outside walls.

Removing 7 feet and placing 6 foot wide french door (presumably windowed not solid wood) is going to produce cold air which gets sucked into radiators elsewhere. So from the cold source you will notice a continuous draft at your feet. In addition to that you are removing 33% of that room's heating capabilities so it will likely feel colder than it used to.

If you want to combat this issue then can look into placing vents in every floor bay for that 6 foot door span so that the cold air can be exchanged for warm air efficiently. as you will get zero heating benefit from having the radiator beneath your floor.

Ignoring the information about an existing window nor the french door of similar size your question boils down to:

I want to remove 33% of the radiant heat from a single room, what will happen?

  • Unless I have missed something The ones I have installed have been in the slab not in the walls , as heat rises warmth from the floor will rise and I really liked warm floors in my garage hind sight I wish I did all the bays instead of 1 but then it takes forever to warm things up if you turn it off to save $ – Ed Beal Jul 1 '20 at 20:19
  • Yes, look up Slant Fin baseboard heating. – MonkeyZeus Jul 1 '20 at 20:53
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    @EdBeal I recently did some work on an old house on our church's property and it had some old style radiators as well as hydronic baseboard heating. I think that's what the OP is referring to. They were actually kinda cool, they had louvers on them that you could close to minimize the convection and thereby limit the amount of heating. These kind of questions are hard to answer, without knowing more. Like what percent of time was the system running in coldest weather? Does it have zone controls? ..on and on. – George Anderson Jul 2 '20 at 0:11
  • @GeorgeAnderson What you describe is exactly what I have. – DonBoitnott Jul 2 '20 at 11:01
  • @DonBoitnott it would be good of you to edit that additional info into your original question. Not everyone reads all the comments, so it will be lost down here (or possibly deleted in a clean up at some point). – FreeMan Aug 1 '20 at 16:18

7 feet? That is one third of the radiator. Unless it was massively oversized when it was installed then the room will take longer to heat up to temperature and may well feel cold.

Also, if the walls are insulated, adding the french windows will increase the heat losses anyway so you have two negative effects - less radiator and more heat loss.

So you might find you will need to compensate for that.

  • I'm less concerned about the door, as there is currently a 6' window in that space already, so really I'm swapping one giant hunk of glass for another. – DonBoitnott Jul 1 '20 at 18:53
  • @DonBoitnott missing out the window was not helpful, but the answer still stands. – Solar Mike Jul 1 '20 at 19:11

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