How to block door for winter?

[JP_]

Will you still want to use this door in the winter? You could get a 5cm sheet of kingspan insulation, cut to size and tape up the edges, and push it in. Won't look pretty but will insulate. Bear in mind that condensation will likely form on the door as moisture will bound to get to it, but you could always open the door from the outside to wipe down when it is bad.

 

[conny]

Even though you have French doors in the next room you should not rely on them as a fire exit in case you can't get in to them.
Can you determine where the main draughts are around the door and fit some sponge draught excluder?
Regarding the glass panel a piece of rigid acrylic sheeting placed over a layer of draught excluder around the edge of the frame and held in place with some clips will provide an effective double glazing system. Put a 'sausage' across the bottom of the door a a brush/rubber draught excluder strip screwed to the bottom of the door edge.
Using these methods the door would help reduce the cold coming in and still retain it as a means of escape in the event of a fire.

If you don't use the keyhole from outside you can also simply put a bit of Sellotape over the hole to prevent draughts coming in there but leave the inner one clear so you can use the key to lock up.

 

[Toria J]

'Just' the single glazing may not account for the cold you feel from there.

First, I would check and replace the weather stripping/draught excluder tape to a thickness that really squishes when you close the door. Check the threshold too.

Second, I would look at if the putty/beading is leaking air and needs redoing. I recently replaced the putty on one of my doors (with butyl tape) and the whole thing feels a lot more substantial. While you're there, you could see if it could take a thicker pane of glass.

Third, check the joins of the door. A few years ago at my last rental property, I filled/glued some gapping joints and repainted a door, and it totally changed the feel from flimsy to solid. The weather stripping somehow seemed to work better too.

Fourth, there's room attach a rail above the door frame to hang a nicely heavyweight curtain there.

Wood can be a really good insulator and the door looks in decent enough condition, so unless the owner is flush, they may not want to replace it.

 

[securespark]

round sausagey draught excluder at the bottom

MMMMmmmmmm sausages!