Boilers
and Heat Sources
The market is flooded with different brands
of outside wood burners. You have choices and we want
you to shop brands and make the best possible investment
for your home.
There are some basic guidelines to follow.
All “traditional” (I’ll talk more
about non-traditional systems later in this note) outside
wood burners fall into one of two categories: Open Systems
or Closed Systems. Some call themselves “semi-closed”.
In short, an open system is a firebox
surrounded by water that is vented through the roof
to the air. It’s literally a pot of water around
a fire. These systems work but there is some maintenance
involved that is very important. Open systems that are
vented to the air will have large amounts of Oxygen
in the water. Oxygen + Water + Steel = Bacteria &
RUST! Most of these open systems will offer you some
kind of water treatment system – those treatments
will help. Like I said, open systems work – I
don’t mean to sell them short. They’re relatively
inexpensive to build, need minimum licensing, and almost
too simple to install wrong.
Stainless steel; don’t get involved
in the on-going arguments of what grade of stainless
is better. The brands with the harder steels claim they
do a better job of preventing corrosion, the brands
with the more malleable steels claim less risk of cracks.
Truth is – either will work for a reasonable time
if you do the maintenance.
Conversely, a closed system is not vented
to the air. It has an expansion tank that absorbs the
expansion of heated water. Unnecessary oxygen is removed
from the water with an air separator. These systems,
if kept closed, do not have the corrosion issues or
water maintenance issues of open systems. Typically,
they have substantially less water also. Most closed
systems are designed for rapid heat transfer and do
not store heat energy in the water but in the wood.
No, they don’t explode. Some uneducated
competitors want to offer you scare tactics by making
unsubstantiated remarks. No company would be in business
long making dangerous products. Actually, closed systems
have more protections and safeties in place than any
open system.
Nothing is perfect, but closed systems
will provide a longer stove life, cleaner water and
longer lasting components like pumps and valves. However,
closed systems sometimes require licensed professionals
to install them and do include more components that
tend to drive the price up somewhat higher.
As far as burn time, and wood usage. It
has more to do with the control of the draft and the
quantity of water sitting outdoors than with brands.
The more water – the more heat loss…simple.
Also, the ability to seal the draft for air tight efficiency
is important.
One more factor to consider when looking
at traditional outside wood burners: ash maintenance.
You need a convenient way to remove ashes from the system.
Some have ash drawers, some have ash augers and some
just sell you a shovel. One small hint, stove grates
do not burn out in outside wood burners, they just don’t
burn hot enough. Try to find a system that has a easy
way to remove ashes from the stove without shoveling
the firebox.
Recently, there has been a surge of “non-traditional”
or “high efficiency” wood burners. You can
read more about that in the next section.
One Last topic – Dual Fuel
The answer is yes and no. I have dual fuel systems available
but I don't recommend them from our brands or any other
brands. Wood is a large, solid fuel burnt in a large
fire chamber with large quantities of water; oil or
gas are molecular fuels burnt in small fire chambers
with small quantities of water. Many manufactures of
outdoor wood furnaces promote dual fuel units with advertised
efficiencies of 80 - 90%. These numbers, however exaggerated,
are based on "flue efficiencies" - this means
80-90% of the oil or gas is burned before exiting the
flue. Don't be fooled, that doesn't mean they've successfully
heated the large gallons of water surrounding the huge
fire chamber. The more water a system has the more BTU
energy it takes to heat it. Oil or gas cannot heat a
wood burning water stove effectively.
What Cozy Heat recommends is the use of
a wood boiler set in series or parallel with an oil
or gas boiler. The cost of an oil or gas boiler is frequently
no more, and sometimes less, than the additional cost
of "dual fuel".
I've heard numerous "horror stories"
about the "dual fuel" systems using a full
tank of propane and the house freezing while the homeowner
is gone to Florida for a week –
Don’t let this happen to you!
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