Rad placement query

[Kaymo]

Hi all,
I have bought a 2nd radiator to fit in a large-ish downstairs room. The first one has been fitted under the north facing bay window.

I am trying to decide where to put the new radiator and there are two options;

Outside Wall with closed up fireplace - this is probably the best place logistically as there is not likely to be anything else here but I am concerned that I would be exiting a lot of the heat into the chimney stack through the vent. I am pretty sure the chimney is blocked anyway but would be concerned about covering up the vent, I usually put reflectors behind the rads and this would not be possible with the vent.
Inside wall, just inside door from hallway - This is not as ideal with regards to the layout of the room which I would have to rethink, but thought there might be a significant benefit to having the rad on the inside wall with regard to heat loss?

Any thoughts, or am I over complicating this?

Thanks,
Kenny.

 

[PrenticeBoyofDerry]

If block up the chimney vent, you will prevent good air circulation within stack. Could lead to sooty condensation problems.

 

[tryitandsee]

Large rooms with a rad one end draws cool air along the floor to the rad, heated air rises off the rad past the window over the ceiling and the resulting cooling air back along the floor again, just where your armchair is!

Try and place the rad somewhere that will balance the air flow.

I should think a rad in front of the closed up fire place would be ok. Cut the reflecting foil around the vent, or better still, make the vent smaller as now getting the benefit of warm air near it adding to prevention of damp coming down stack. Only needs a trickle vent!

 

[Kaymo]

Thanks Try and see, I suppose I could put the foil over the top of the vent and then just cut slits in it where the vent is. I had also been thinking of cutting out a section of the lathe and plaster behind where the radiator will go and fitting some insulation in (leaving a space behind the vent) so that the radiated heat is not lost through the plaster.