Why are sheets colder in winter when the room isn't?

[kanicbird]

@Pygmy Rugger

No. There’s no such thing as cold, only lack of heat. And lack of heat can’t radiate.

I was simplifying, but it is radiation which is the difference. The sheet is radiating to the ceiling and the ceiling to the bed. There is net heat transfer from the sheet to the ceiling since the bed is warmer and will radiate more.

Lack of heat can and does act as a sink for radiation.

[The_Flying_Dutchman]

Temperature in a heated home is rarely consistant. Wherever you have windows with an R rating of 3 at best copared to R20 in the walls and even higher in the ceilings, heat will radiate from nearby objects to the windows.

Your bed is probably next to a window. All day heat will radiate to the cold window a lot faster than the influence of ambient warm air on your bed.

And you probably have forced air heating.

[Santo_Rugger]

Yet another example, satin sheets usually feel cooler than cotton. And, as stated earlier, flannel sheets feel even warmer. Although radiation plays a part, and I’d have to do the math, I would think convection in the room would be more significant than radiation to outside.

@kanicbird

I was simplifying, but it is radiation which is the difference. The sheet is radiating to the ceiling and the ceiling to the bed. There is net heat transfer from the sheet to the ceiling since the bed is warmer and will radiate more.

Lack of heat can and does act as a sink for radiation.

Thank you.

[Rusalka]

It is always warmer near the ceiling, your bed is near the floor. The difference is exaggerated in the winter.

Not the entire explanation but part of it, along with Colophon’s and others. You probably don’t have the heat blasting when no one is in the house, (why would you?) and the sheets don’t heat up as fast as the surrounding air when you come home and turn up the heat.

[Frisco]

@Rusalka

You probably don’t have the heat blasting when no one is in the house, (why would you?)

I do have people in the house nearly all the time. I realize some people cycle their heat and air during the day and night, but I don’t. That’s one of the reasons I started wondering about the sheets feeling cooler on the coldest days, since the temperature in the house is pretty stable.

[kanicbird]

@Pygmy Rugger

Yet another example, satin sheets usually feel cooler than cotton. And, as stated earlier, flannel sheets feel even warmer.

flannel is warmer because it’s ‘fuzzy’, which holds the material away from your body, and allows a airspace of heated air between your body and the colder fabric. Standard cotton weave touches much more of the skin, and allows more direct conduction between the fabric and your skin.

[Kevbo]

I think the heat loss via radiation explaination has it nailed.

It may be partly psychological as well: In the summer, cool sheets would be a good thing. “refreshing”.

If this really bothers you, or you just want to pamper yourself, use an electric blanket to preheat the bed. They have gotten a bad rap, but can’t possibly do any harm if you turn it off before retiring.

[Quiddity_Glomfuster]

@Elendil's Heir

I dunno, but if you get cotton flannel sheets, the temperature differential (actual or merely perceived) isn’t nearly as noticeable, and you’ll sleep more comfortably in the winter, too.

Hear hear! Loves me my winter flannel.

The explanation about why flannel is warmer when you’re under it makes sense, but how come it is also much warmer immediately you climb under it? Your body heats it very rapidly? It retains vestigial body heat from morning?

[Tibby]

@Mangetout

<snip> Insulated objects, such as the inside of your bed, and larger objects, such as human corpses, will take time to approach equilibrium - and will therefore tend to always be warmer than the coldest end of the temperature range, but cooler than the top end. They will tend to remain at the average room temperature.

Avoidance of extreme temperature fluctuations is precisely the reason I cover my bed with human corpses in lieu of bed sheets.

[Musicat]

Could humidity be a factor? My house has about 10% humidity in the winter and around 50% in the summer. I make no attempt to regulate it; it just happens as a function of heat applied and windows opened.

[LSLGuy]

I think a lot of the issue is the OP’s assumption that when the thermostat in the central hallway says, say, 70 degrees, then it is exactly 70 degrees throughout the house.

I suggest you get a thermometer (like this http://www.kmart.com/catalog/product.jsp?productId=124522) & put it on your bed a few hours before bedtime. Check the termperature just before climbing in to the cold sheets. Do the same thing in the spring, summer & fall. I bet you find a 5+ degree temperature difference regardless of your heating/airconditioning habits.

The thermometer doesn’t have to be expensive or accurate; all we’re checking for is the change from month to month.

I have several similar to the one I linked to and I have them scattered around my house. Despite zoned heat & A/C & stairwell barriers, my new-construction house has hot & cold areas of +/- 5 degrees versus thermostat temperature. And guess what: generally those spots swap being colder than desired in the winter for being warmer than desired in the summer. I bet you’ll discover the same effect at your house.

[Myglaren]

@kanicbird

I was simplifying, but it is radiation which is the difference. The sheet is radiating to the ceiling and the ceiling to the bed. There is net heat transfer from the sheet to the ceiling since the bed is warmer and will radiate more.

Lack of heat can and does act as a sink for radiation.

I am reminded of this:

When a quiz or exam rolled around, you never knew what to expect. The best study technique was to get a good night’s sleep and pray a lot. For example, in heat transfer, the final exam included the question: “The Bible describes how to make ice on the desert. Please describe the procedure and explain how it fits your knowledge of heat transfer.”

No one knew the answer. Doc chuckled and told us we should read the Bible and learn that on a still, clear night in the desert, if one dug a shallow hole, lined the cavity with straw and placed a ceramic pan with a thin layer of water into the straw-lined nest, then there would be minimum conduction, little or no convection, and radiant heat transfer to outer space would control. Since outer space has an equivalent temperature of minus 400 degrees F, and radiation is governed by the difference between the absolute temperatures to the fourth power, you can truly make ice in the desert.

From This quite fascinating article.

[Mangetout]

I’ve heard of making ice by radiative cooling before, but I don’t think the technique is detailed in the Bible - if I’m wrong about this, please could someone point me to it?

[Myglaren]

Well, I’m damned* if I’m reading through the bible to find a cite.

*more than likely!