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Night Sweats, a cause

Night sweats, serious night sweats, the type where you wake up literally drenched, soaking wet, have plagued me on and off for years; they really can affect your health and wellbeing.  Primarily this is a problem in the summer, but I have also had problems in other seasons.  I will try to explain one major source of these sweats, why they tend to only happen at night, and a straight forward solution that should help many, but sorry, not all "sweaters" out there!

It may not be you that is the source of the night sweats, but you can certainly implement the solution.  I have had the problem in several homes and I partially cured the sweats in my previous home, and now finally in our current home, I have found one cure.

You know it really does not matter how much air conditioning you may have, you may still sweat heavily at night.  If you are like me, you at least like to have a sheet at night no matter how hot it is.  Drafts can still feel cold, especially if you are sweating.  But in between the drafts, you may be burning up, which may impact your health in numerous ways.  Surprisingly you may accidentally cure, or at least reduce, your sweats by the color sheet you choose.  A light color may keep you cooler, while a dark color may make you hotter. 

The source of your discomfort, radiation!  What?  Well, infrared radiation, the stuff that transfers heat from the environment to your body and from your body to your surroundings.  This transfer of warmth does not involve contact or airflow.  The two other forms of  transfer are conduction and convection, respectively.  Just about everything radiates infrared.  It is just that the thing that radiates more wins the battle when you want to be cool!

If your bedroom is on the South side of the house your problem may even be worse, but in my case I was having pretty severe night sweats even though our bedroom is on the North side of the house.  The culprit, is the sun.  The sun? But it is "night" sweats.

Heat soak, one source of night sweats

I have coined this term for a situation in your home that can be the cause of your sweating; again regardless of your air conditioning.  If your bedroom is directly under your home's roof then your likely to have this problem.  If your bedroom is adjacent to a brick wall facing west you may have this problem, and if so, this article will only suggest a solution.

These blankets are so cheap you should always have them just for emergencies!

There is no good way for you to block the radiation that propagates through your ceiling or through that West facing concrete or brick wall.  One thing that would block it, is one of those aluminized space blankets, but what's the problem with that?  The blanket reflects your own radiation back to you!  Great if you are freezing in the great outdoors, but not if your already sweating away a two hours after nightfall.  With all the radiation pouring in from the attic, or from the brick wall, you cannot air condition radiant heat away!  You either have to block it, or prevent the surfaces involved from warming up in the first place.

The tricky part with "heat soak"

The time delay.  During the day the sun literally cooks your roof, shingles absorb a lot of thermal radiation.  The warmth propagates slowly through the shingles and then begins to transfer by radiation and conduction to the plywood sheathing of your roof.  Then onward to your joists which are a substantial thermal mass.  The heat then radiates down to your insulation and ceiling joists.  The energy takes a substantial time to propagate through these thermal media.  Radiation can easily propagate deeply into your insulation.  The insulation primarily prevents conduction and convection.  But all day long the insulation below your roof is warming from the top down.

It seems it does take hours for the infrared itself to propagate all the way through the insulation finally reaching the drywall which is above your head in the bedroom.  What I have found is the "heat soak" may not begin to radiate seriously into your bedroom till eleven o'clock or perhaps midnight.  And you do not start to sweat right away, because all your bedding is nice and cool, and oddly enough if you use a quilt it will take a small amount of time for the thermal mass of the quilt to soak up warmth from you bedroom ceiling.  But, I guarantee you, there can be a lot infrared pouring down from that ceiling insulation.

This is also true of the west facing brick wall.  All afternoon the sun bakes the bricks, the temperature increase slowly propagates through and is stored in the thermal mass of the bricks.  The inside of the bricks then begin to radiate to the insulation in the wall, and wall studs, and finally to the drywall, perhaps adjacent to your bed.  Either way there can be a very large time delay, before the source of your night sweats starts to roast you! 

Reflective Foil partially installed in my attic

There is one quick elegant (at first) fix.

You may solve your night sweats problem by installing reflective aluminum foil, either below your roofs rafters, or even just laid out on top of the ceiling insulation.  There is even a "shredded" product that can be blown in.  It is most desirable that this foil be free floating.  If it is in contact with a radiation source, the foil will just reradiate the energy!

While this solution seems elegant I feel it has some problems.  If it is applied on top of your insulation it may seal in some of the moisture that is slowly migrating through the drywall in your home and then escaping through your attic.  This is a normal, desirable, process that prevents your insulation from prematurely aging, or perhaps even getting moldy!!  The aluminum material attached to the bottom of your rafters is a somewhat better choice, but you know, your roof itself still bakes!

Yet another problem and benefit of the "foil" solution.

During the day in the winter my heater rarely runs.  Why?  Solar energy gain.  Again, just infrared radiation being absorbed by all the surfaces in your home.  All that mass in your trusses, joist, and insulation can store a tremendous amount of solar thermal radiation, keeping your home warm during the day and well into the night time.  That West facing brick wall can be a real energy saver in the Winter!  The aluminum foil solution prevents all this free solar energy storage; so you lose the "solar gain".  The foil does however prevent radiative loss from your living space into your ceiling insulation, an energy savings, especially on the long sunless weeks you may have in Winter.

Even the air in the attic contributes to you night sweats!

Even the air in an attic gets hot.  Many homes have a "peak vent".  This peak vent is there to keep the temperatures in your attic from getting excessively high.  The vent is primarily there to prevent damage to your home from excessive temperature, and even worse, humidity build up below your roof.  The temperatures will still get quite high with just a peak vent.  From my perspective most peak vents are really heat traps!  They do have to prevent rain from entering, so they tend to be shaped in a way that traps hot air.

So what's left to stop the nightly sweating?

The attic exhaust fan!  If done correctly, it is by far the best solution.  The exhaust fan removes the hot stagnant air frequently and only when necessary.  Why is this so important?  The air in the space below your roof becomes a "thermal radiation sink", a sink that can continually be exhausted, hopefully, well into the evening when radiation  is still trying to propagate through your insulation.  The air not only acts as a radiant heat sink, but it is also a conductive and convective source of dissipation.  It also cools everything in the space below your roof.  The aluminum foil solutions still allow heat build up in portions of your attic.  The airflow will even help cool your shingles during the day.  It helps remove moisture as well.

 The attic fan ready to install
 Attic fan near the peak of the roof

Some say exhaust fans remove too much moisture, excessively drying the lumber in your trusses.  I do not know about this, I think the key is not having excess air flow.  You must have proper air inlets to your attic.  Most modern homes have full "soffit vents" around the entire perimeter of the house.  This is ideal if you center your fan along the length of your home you will have air circulating uniformly throughout the entire space, maximizing the heat removal.

And you can have too much of good thing.  A fan that is too powerful may "suck" the air conditioned air out of your house, perhaps bringing back some of your sweats.

A very big benefit is energy savings.  The radiant heat slowly spreads throughout your home, requiring more air conditioning than you truly need.  With less "inbound" infrared radiation you may find you can set your AC thermostat a little higher and still be comfortable.  You might even find you like a light blanket!


What about that brick wall and my night sweats?

I have never tried this, but, would suggest attaching to the brick wall, heavy duty 4' x 8' treated trellis spaced an inch or two off the surface of the brick.  Perhaps use treated 2" x 2"s or small segments of PVC pipe as stand offs.  Tapcon Screws are an easy to use fastener for brick or concrete.  They even come with a masonry drill bit to make life easy.  Also consider allowing room at the ground level for planters if your brick wall is adjacent to black top.  There are very fast growing ivy's that you can plant in the Spring.  You may want to find ivy that will only grow on the trellis not the brick.  I believe ivy on brick can be harmful.  The ivy will grow up the trellis and shade the wall in the summer.  Then in late fall cut the ivy, or not, let it die and dry on the trellis.  You will still have your "solar gain" in the winter, and hopefully your night sweat will be gone in the summer!

If your sweats are not from your infrared radiation or brick walls some other thoughts

Mayoclinic.com Night-Sweats 


Night Sweats are virtually gone

Since installing the exhaust fan (and setting the thermostat properly) we are much more comfortable at night, in our air conditioned home.  How could that be?  RADIATION, is a killer!  It was important to get the thermostat setting on the attic fan "correct", and I do have a different setting than the manufacturer recommends.  The topic of another article, please take a look at "Exhaust Fan Setting".

Hope this helped cure your sweaty nights!









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