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Sometimes we just need to vent...saunas that is - by Craig Lahti

As the Ancient Roman classical poet Ovid wrote, "Sickness seizes the body from bad ventilation."  The same can be said of bad ventilation and its affect on a sauna.


When the majority of saunas were heated by burning wood, either in a pit or later in a stove, the necessity for ventilation was understood.  Both the fire and the bathers required a continuous supply of fresh air to function.  If ventilation was not sufficient, the fire would consume much of the oxygen, and the bathers could face suffocation.  What the sauna bathers also learned was that depending on how the vented the room, the environment of the room changed.  Proper cross ventilation not only provided the essential fresh air to breathe, but it also directed the convection currents flow in the room, so the heat was more evenly distributed. Coanda Effect


With the introduction of electric stoves, the importance of proper ventilation began to be lost.  Electric stoves do not consume oxygen in the heating process, so it has often been assumed that the heater did not require ventilation to work properly.  Since the heater is not consuming oxygen, the bathers are not competing against the stove for a fresh air supply, so the bathers need for ventilation is also theoretically reduced.  When the sauna is installed in a left over niche, ventilation is often not considered, so the location of the sauna is not always ideal for a proper air intake and exhaust vent.  


Unfortunately, while the idea of less oxygen being consumed is correct, the thought that an electric stove does not need ventilation is wrong.  To be clear, the ventilation to which I am referring is not a mechanical vent powered by a fan or blower; rather, the ventilation is simply the installation of an air intake valve and an exhaust valve.  Though mechanical ventilation may prove beneficial in some installations, the equipment must be properly tested to withstand the heat and volume of air found in a sauna.  In most cases, the cost and work involved in installing such a system would not provide a substantial benefit to the sauna experience, so for this article, we will focus on the traditional cross ventilation found in most sauna heater installation manuals.


As discussed in previous blogs, traditional saunas provide heat to the sauna room in three ways.  The first is conduction with the heating elements heating the rocks through direct contact.  The second form, which is what we will focus on for ventilation, is convection where the elements heat the air.  The final form of heat is radiant (infrared) heat from all surfaces which have been heated by the hot air.  Improving convection heat in a sauna will improve the performance of the other heat sources as well.


Why is ventilation important for convection heating?  As we have heard since elementary school science classes, heat rises.  Heat rises because the hot air is less dense than the cool dense air that it replaces.  This movement of air is called convection current, and if you can picture a hot air balloon flying, you can see convection currents at work.  When the burners are fired, the balloon rises.  As the vent flap is opened or as the air cools, the balloon comes down.


In a sauna, convection currents are responsible for the stratification of heat.  In a room with little to no ventilation, the hot air will rise from the heater, and it will stay towards the ceiling of the sauna.  Since most saunas are well insulated, the heat does not dissipate from the room quickly; instead, the heated air slowly cools and replaces the cooler air beneath it, but since there is no place for the existing cool air to escape, the cool air remains in the room (this is why some saunas will have bathers complain of cool legs or feet while sitting on the low bench).  In a sauna with this construction, the current of cool air drawn into the sauna heater is reduced, so there is an increased chance of overheating the high-limit switch that protects the sauna and sauna heater from overheating.  The thermometer mounted on the back wall of the sauna one foot down from the ceiling may show a temperature of 140° to 150° F, so the bather is often confused as to why the high-limit switch has "tripped".  It has tripped due to poor ventilation.





Convection air flow

In a well ventilated sauna, the heat is more evenly distributed from floor to ceiling.  There will still be a stratification of heat, but it will be less pronounced.  With proper ventilation, a cool air intake will be installed in the wall at the base of the sauna heater, and an exhaust vent will be installed on the opposite wall, approximately 20-24" above the finished floor.  The cool air intake provides fresh, cool air to the sauna heater.  Though the air is quickly heated and rises out of the heater, the cool air helps to regulate the temperature of the sensor connected to the high-limit switch.  Because of this air flow, the high-limit switch will seldom become overheated, so the heater becomes more reliable.  As the heated air rises, the cooler air is displaced; however, unlike the poorly vented room, the cool air is pushed out of the exhaust vent.  By exhausting the cooler air, room is made for the heated air that has cooled slightly to be moved to a lower elevation.  This movement of heated air and replacement of cool air will allow for a more even heat distribution throughout the room.  These convection currents are what make a well ventilated sauna room work so well.



There will be times where cross ventilation cannot be optimally installed, but it is important to find a way to incorporate some form of ventilation.  Even installing an air intake by the heater and installing an exhaust vent on the opposite side of the front wall is better than no ventilation at all.  Besides the benefits of better heater performance and a better distribution of heat, a well ventilated sauna will likely smell better and will dry quicker after being cleaned.


To learn more about installing a sauna and to discuss your installation and how to incorporate proper ventilation, contact your local dealer.  For more information on saunas, request our brochure.

 



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2011-06-20
Dalton (egs7@egsi.com) wrote:
IMHO you've got the right asnwer!