Discussions

I have one room in my house that is so cold this winter. You can just feel a draft in there all the time. Last winter it wasn’t like this. If I leave the door closed overnight it gets down to 10/12. where the rest of my house is a comfortable 20/21 or so. I’ve checked the window and it’s right shut. I was wondering if you can rent a thermal gun somewhere to scan your house and see where your heatloss is coming from.

Is there both a heat register and a return air vent in the room? If there is no return air vent, then warm air from your furnace will not efficiently enter the room when your door is closed.  
 
You may also have a draft, but leaving the door open will help the temp stay more consistent.  
 
If you think it is drafty, you could get one of those incense sticks and check around the room to find the airflow.  
 
I don’t know about renting a digital thermometer or whatever, but that may work to some degree if there is a stud cavity that has no insulation or something.  
 
Any chance that room has an attic access hatch? If it isn’t sealed well, cold air will be drawn into your house any time it is being exhausted somewhere else, like a bathroom fan or a dryer.

Room is a main floor bedroom. Used as a toy room. It has 1 window and 2 registers both are open and a return air thing that is just a vent that lets air flow into my living room kinda if that makes sense(house is an older wartime house) . I only close the door cause I notice the cool that comes outa that room. I’ve been thinking about putting plastic on the window. But it’s a newer white vinyl style window so I don’t think that would be the issue.

Maybe not the window itself, but if it was replaced (obviously was if it is PVC), then it is possible they didn’t insulate and seal around it properly, which would cause a draft around the outside.  
Settled insulation is likely as well in an older home. Insulation will compact, so the bottom 2-3 feet will be insulated, although not well because it is too compact, and the rest won’t be insulated at all. If the exterior walls are colder up high than they are down low, that could be a contributor as well.  
 
Lots of things can be at play as you can see.

Also I just saw a digital temp reader for $25 in classifieds

I have a calibrated high resolution thermal camera that I use to look for major heat loss areas in residential and commercial buildings. I am booked up for about 2 weeks right now, but if you would like to schedule me to come by near the end of the month send me a PM and we can go from there. Typically I charge in the range of $100 for a single bedroom or $300 for a typical residential house, but depends on size, complexity and requirements of the client.

i would check to see how many windows and what type of shape they are in and weatherstripping around the door?

Is there heat coming out of the registers when the furnace runs.  
Slowly run your hand around the window frame and feel if there is a draft anywhere

In your original post, you said that the room being cold wasn't an issue last winter. So, the obvious question is, what has changed since then? It doesn't sound like you have had any work done or that you changed the window, so I think you can eliminate that as being the source of the cold air. Is it possible that there is a damper on the supply that has been inadvertently closed? If it is just the one room, I would suspect that it is a supply issue and not and overall structural issue.  
 
Hope this helps.

https://www.thermal.com/compact-series.html  
 
Doesn't hurt to have one around. We have a phone connected thermal imaging camera for basic stuff. Works fantastic. Find drafts, lack of insulation, etc.

Just looked at your link witch one do u have I would not mind getting one for myself if u say it works.