Methods to stay warm enough in a castle:
1. Metal braziers
2. Heated stones and bricks
3. Body heat, combined
4. Layered clothing
5. Carpets and draperies
6. Hot alcoholic drinks
7. Physical activity and work
8. Animal warmth
9. Hot, spiced foods
10. The central hearth

I was homeless for 20 years and used candles, hot stones, and hot coals in a metal bucket to keep my handmade house warm in the winter. I also used blankets as insulation and sheets of thick plastic and cardboard for my walls and roof. I lived with just me and my cats like that for 20 years.

I've visited many castles in the UK and they all had huge fireplaces.

We had an ice storm in western Oregon in 2021. We had advance warning so I got a bunch of fire bricks and tea candles. Place about 5 tea candles between a couple of bricks and the heat was sufficient to cook with and warm rooms.  Keeping a pot of water over the bricks/candles added about 5+ degrees with the humidity.  Kerosene lamps throw more heat but aren't really good to cook over.  I had plenty of small camping lights that ran on batteries.  We were without power, phone, internet or even water for 8 days. Others were out for 3 weeks or more.  I hung tapestries in doorways so only the rooms being used got heated.  It was quite an adventure. I also cooked ahead of time so that I had plenty of good foods to heat up. Also got sandwich materials, teas, drinks, etc.  I downloaded a number of movies and had a small power station that would run a laptop so I had some entertainment as well.  The advanced warning helped. Also had a weather radio that constantly advised of temps, etc.

In Germany we have more than 25000 Castles and Palaces. There are many "wooden Walls" and " wooden rooms"  found to install in the wintertime. The people weren't in big rooms with stone walls, they made the rooms smaller and cosier with this woodwalls. (Room in a room )

Most castles, especially in medieval times didn't have bare stone floors. There were rushes or straw several feet deep with a woven grass/rush mat over the top.

The rushes were burned and replaced routinely.

Castles also did have "rich tapestries." This was less for decor and more for insulation of the walls. Often the curtains or tapestries were hung away from the walls leaving a large air pocket that helped insulate the wall. In Shakespeare's Hamlet, it was easy for Poloniius to hide behind curtains.

Beds/benches were raised over an oven basically where servants slept. They were built into the castles themselves.

Richer people slept in raised bed boxes. It was a box that could close up for privacy and warmth.

Although it was less popular after the fall of the Roman empire, hypocaust systems basically created a basement furnace that allowed hot air to flow through furnaces to upper floors.

Many castles were also lime washed or coated on the inside with chalk. The white walls better reflected heat from candles, braziers, torches and animal oil lamps.

The castles themselves were actually warmer in the winter than most people think simply due to the extreme thickness of the walls (in some places more than 5 feet.) Medieval castles rarely had glass windows and windows had shutters and parchment coverings for winter.

Most castles also had surrounding outbuildings attached to the structure, again providing extra insulation.

Castles frequently were inclosed within a fortress or wall. This also helped insulate the castle from winds.

*Note: I began writing this before watching the entire video. Sorry if there's repeated information.😁

No AI were harmed in making this video. But - if you try handling red hot rocks, or sipping near-boiling drinks, or slurping very hot porridge, or barehand bread fresh from the oven, or any stunts involving fiery coals, you may well suffer painful burns.

Ladies and gentlemen. To be exact, lifting those heated stones (some glowing) by bare hands, as in this video, would not have been possible without causing serious damage and burns to the skin. Don't try this at home! A glowing hot stone would also have caused fabrics and animal skins to burn. Obviously AI doesn't have our human feel.

The walls would have been plastered, and when occupied by the lord and upper class, the walls hung with tapestry and other hangings.

My grandmother in Mississippi used to do this technique when it was cold she would take a shovel full of hot coals and place them in the back bedroom fireplace an hour before bedtime and heat up bricks and wrap them in blankets at the foot of our beds and it was awesome and she would get up at 5:00 in the morning and make breakfast year after year like clockwork

Ok. Cows, horses, sheep, dogs and goats can warm a room, but I draw the line at rats

Dogs: it is a three dog night, that is what it refers to.

When I lived in the Yukon, the government built nice looking cabins for some of the first nations inhabitants.  However some of them chose to pitch their double hung wall tents outside in the yard and sleep in them.  They hung one wall tent inside a pole framework for the inner tent and then an outer tent over the framework.  That left an insulating air gap between the two tents.  The whole structure was raised over a wooden floor and short wooden side walls (to provide more head room).   Someplace in the tent, a small wood-burning heater was placed and vented through the roof using metal pipe.  I never slept in one of these tents, but I was told it was quite comfortable in the coldest weather as long as a fire was burning in the small wood heater.  

For myself, I found that food was the foundation of warmth.  As long as my body was well stoked with substantial food with plenty of fat, I stayed warm and could work hard.  When I ran through the food, my body would start cooling down regardless of what I was wearing or what I was doing.  I found that a down vest was usually enough warmth for me down to freezing (32 F/0 C).  I would add a jacket or light coat over the vest, down to 0 F.  In deep cold weather, I started with a layer of heavy, one piece wool longjohns and added a heavy wool shirt and thick wool pants.  I also wore wool socks and felt-lined snow boots.  A breathable, windproof coat over a thick vest seemed to be able to withstand most anything down to -65 F.  I kept all my clothing loose, not tight, including my boots.  It was important to let enough air circulate inside the clothing to keep me just a little cool so that I didn't build up moisture from my body inside my clothing.  And, depending on weather conditions and my activity level, I put layers on or took some off to maintain that slightly cool feeling.  On mornings when I had to walk several miles to work, I carried my parka, even at the lowest temperatures.  In the evening when I walked back to the cabin, I wore my parka with the hood snorkeled up and feeling chilly because I had burned through almost all my food and needed to eat.  As long as  you have high calorie food in you and some insulation and a way to block the wind, you can stay pretty comfortable at pretty cold temperatures, assuming your metabolism is working correctly.  I have read of people on arctic expeditions starting the day off by eating a stick or two of butter before the rest of breakfast.  The thought might turn your stomach at normal temperatures, but when you spend many hours outdoors in windy, deep cold, the fat is welcome.

In the North of Germany, all living beings on a farm were kept in one large hall house, als already the Vikings did. There was a fireplace in the middle of the hall, surrounded by cobblestones. The stables of the cattle and fowl were in one half of the house, the rooms for humans in the other half. People slept in wooden compartments which were not much larger than a wardrobe. They can still be seen in some museums. They had sliding doors, nicely painted with ornaments. They used bed pans made of brass and a wooden handle which were filled with hot coal and were pulled over the matress and duvets, slowly enough to warm the bed, but not to scorch them. There was a long bench around the sitting room unter which the young chickens ("Stubenküken") were kept to protect them during their first weeks of life.

Our furnace went out one year in January . . . and it was COLD!  We piled on blankets, put us two to a bed, used the fireplace, and wore layers until the new furnace got installed.
Fortunately, we're visitors to the local Renn Faire and we each had a heavy boiled wool cloak at our disposal. I also knit, so we had scarves, mittens, and hats aplenty.  Warm soups, teas, stews. and other high calorie food kept us going.  Those old techniques work!

Spent 3 days in a house with no heat with -30 degree with windchill in January 2009. The basement flooded the heat out, but I still had electricity. I cornered myself off in my 10x10 office with a small electric heater and a mountain of blankets as I pumped a flooded basement with a hose and a swimming pool pump that kept freezing meaning I had to go outside to bring it back in to thaw. My ex and kids stayed at his parents. How I did it, I still don't know.

I don't think I could survive winter without my goose down comforter and pillows. Wool socks and hat worn to bed are also great ways to stay warm.  A modern convenience that is  a fabulous thing is an electric mattress pad.  Preheat it before climbing between your flannel sheets and you're toasty all night!

I had a co worker from The far north, tell me that his family would heat soap stones in the winter by the fire place, and put them in at the foot of their beds to keep warm,. I see that today, you can still order them online for about 47 bucks.  I am thinking of ordering a couple. If you have ever touched a soap stone before, it is amazing how soft to touch they are. Better than Bricks.

I love how, when they're heating the rocks, they take these.....glowing rocks?......out of the fire with tongs, then take them in their hands. 😂😂😂

I lived for 14 years in a house built in 1600's.  It had 32 inch walls which kept the house cool in summer and warmer in winter with a small fire.  In British castles I note that they had tapestries hanging on walls for additional insulation and thick curtains and the fireplaces were huge. Not only that but people wore clothes that had sometimes five layers of fabric, and wore hats and wigs indoors.  As recently as my childhood in the 1950's houses were cold , without double glazing and heated with open fires.  We wore more layers, wool and blankets to keep warm.
The winters have not changed much over the centuries.