Keepers of the Flame

The laws of physics tell us that if you move air over a hot surface you will increase the heat transfer efficiency from that surface.

Many stoves and fireplaces come equipped with fans specifically for that purpose.  Others provide air convection chambers so fans can be added as an option.  Still others have no capacity for fans.

For some the debate for and against fans on stoves and fireplaces is a point of contention with arguments favoring both sides.  Here is our take:

For products with integrated fan designs there’s evidence that efficiency is increased when the fan is in use.  This increase while it is real, may be hard to measure in terms of how it feels.

Stoves and fireplaces heat in two ways radiant & convective.  If a product is designed primarily as a radiant heater, then the presence of a fan often makes little difference in the amount of warmth you experience.  If the product is designed  as a convective heater, then the fan is apt to be more significant.

Keep in mind, most of our stoves and fireplaces are meant to work even when the power is out.  When this happens of course the fan will not function.  While there may be some drop in efficiency it is rarely significant and the stove or fireplace will continue to provide warmth.

Products designed for radiant heating will have very little if any benefit from the addition of a fan.  Where they have been tested, the efficiency difference is approximately 2% – 3%.

The electrical requirement for fans means additional installation cost if power is not already present in that location.  This is especially critical when inserts are installed in existing fireplaces.  Another issue is fan noise.  While fan technology has improved, there is going to be a certain amount of noise when they are in operation.  Controls enable us to lower their operating level and their output, but if the room is quiet you are likely to hear it.  Most of the fans utilized on fireplaces are capable of moving a maximum of 100 to 150 CFM.  This means you will certainly feel the warm air when you are within 2 or 3 feet of the fireplace.  However, this is typically not enough air movement to move heat from one room to another.  Natural air currents in the house will be responsible for that.  

If the fireplace you like and select has an integrated fan – don’t think twice.  It will be great and with or without power the fireplace will still heat.  If the fan is optional on the product you select then consider the expense of adding the fan relative to the benefit.  If it is a high-efficiency fireplace or insert then the fan is not likely to make a big difference.

When is Hot Too Hot?

Radiant heat produced by wood and gas fireplaces warms any object in proximity to the heater.

Most of the time this heat is welcomed by us because it feels like the sun and warms us to the bone.  The byproduct of radiant heat is the gradual heating-up of walls and mantels close to the heat source.   In many cases after a fireplace has been on for awhile, nearby surfaces can be too hot to leave your hand on them or “too hot to the touch.”

Fortunately, the fact that they are too hot to touch does not mean that they are unsafe or likely to ignite.  Going back to the sun, have you ever walked on a wood deck drenched in the sun in your bare feet?  It’s like walking on hot coals.  Still, there is no record of a deck spontaneously igniting.

Once a surface gets much beyond our body temperature of 98.6 degrees F, it starts to feel hot to the touch.  Over the years, organizations like the National Fire Protection Association (NFPA),

Underwriters Laboratories (UL) and the National Bureau of Standards (NBS) have established standards for allowable temperatures on a variety of combustible materials.

Research tells us that for wood to ignite it must reach a minimum temperature of 482 degrees F.

There is evidence that if wood (and some other combustible surfaces like sheetrock) are exposed to sustained high temperatures over long periods of time their ignition temperature can be lowered.  It is at this point that codes & standards converge to tell us what is acceptable.

All this research and testing tells us that the critical temperature for potential danger is 187 degree F or approximately 117 degrees F above ambient room temperature.  It is to this temperature that heating appliances are tested.  When a fireplace is installed, the parameters for safe clearances are laid-out in the installation manual by the manufacturer.  The common denominator is that under extreme testing conditions, the nearby surfaces never reach the 187 degree temperature.

While walls and mantels remain safe at these temperatures sometimes the finishes (like paint or sealants) do not hold-up.  They can blister or peel in some cases.  This does not mean there is a safety concern, but it is a good idea to know what the temperature limitations are of the finishes applied to surfaces near fireplaces.

Too hot to the touch is a physical barrier we learn from childhood, but it is not necessarily a legitimate method of gauging the safety of a fireplace installation.

Technology seems to define and influence our behavior more than ever.  Of course this could just be

the whining of an ageing homo-sapien,  but  for as much promise as technology holds for us there is at least an equal amount of frustration as we adapt.  

When we consider our relation to fire it is not immediately obvious how much technology has

has influenced us.  We have moved from striking flint over dry straw to matches, butane lighters and firestarters.  The origins of camp fire building have evolved to The Top Down Burn.

EPA & Washington State certified stoves have evolved to limit our individual control of the stove or insert.  As long as we operate with dry wood and observe the basic tenants of  the owner’s manuals, it is almost impossible to create a smokey, inefficient fire.  EPA Label.  Yet, for those who believe they can learn nothing new,  fire building can harken back to our caveman roots and create unhealthy smoke and particulates.

Fortunately, fire technology has not stopped with wood burning.  Witness the evolution over the past several decades in gas burning and electric fireplaces.   While some would eschew the use of these sources of fire it is hard to argue that the beauty, style and efficiency of these products is very appealing.  Add to that the relative cost and ease of utilizing these products compared to wood and it is easy to understand their popularity.  Outdoor Great Room Wave or Amantii fire & Ice.

Once again the advancement of these products has not been restricted to their aesthetic qualities.

Over the past several years we have seen the development of  electronic ignition and remote controls that allow the fire to ignite without a traditional  standing pilot system.  These multi-function devices allow users to control flame height, heat output, fans and lights.  They also provide thermostat and timer functions in many cases.  Now we are on the cusp of having our fireplaces controlled by our smart phones (some of these are already in use).  

It’s true that time waits for no Man or Woman,  and like it or not our control of fire is blossoming with our technology.