Inset Stove Design and Testing Part 2

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Insert Stove

Design Factors and Testing

Part 2

An Inset Stove called Firewarm

So to recap -

STANDARD TYPE STOVE:

A standard stove is simply a single sealed box. It can be made of iron - steel  -or other fireproof material.  Let us simply call this:
 

BOX ONE.

A controllable amount of air comes in one end to feed oxygen to the fire - and hot gasses and smoke goes out the other end and up the chimney. The heat from the fire is dispersed both by radiant and convection means from all sides of the stove.

INSET STOVE:

An Inset or Insert stove, by contrast,  is stuck into the wall or chimney breast and therefore it cannot radiate or convect heat - except from the front. That leaves 5 other surfaces which cannot give out any heat

An Inset Stove has TWO BOXES,  one inside the other. The inside box is a complete stove in and by itself.

The outer box is there for ONE PURPOSE ONLY. It is there to create convection air channels to take the heat from the sides, back, and top of the fire box, and GET THAT HEAT OUT INTO THE ROOM. This box let us call it:
   
BOX TWO.

BASIC TESTS FOR INSET STOVES

Apart from getting the fire to burn well and fully controllably in BOX NUMBER ONE, an inset stove needs to have a convection air current established in BOX NUMBER TWO (the outer box, in order to take the heat from the back -sides and top of the stove out and into the room.

TEST NUMBER ONE

What we are testing:

Is the burn rate of the fire fully controllable? This is a basic test for any type of solid fuel stove.

This test is really easy to establish. When the fire is fully lighted and burning really hot, simply turn down both the primary and secondary air controls fully.

The fire should immediately begin to dim down and within five minutes or so should be burning a dim red. After an hour or so - if the stove is in very good airtight condition, the fire should go out completely.

Most stoves are not completely airtight - so the fire may not completely die down but may continue to burn. However, it should only burn at a really very low rate!!

If it continues to burn at a faster rate, you have a faulty stove. The problem could be one of several things. Here are a few to think about:

(a)    Poor door seals.
(b)    Poorly fitting air vents.
(c)    Joints in the stove sections not properly sealed.
(d)    A crack or break in the stove wall. This could happen in manufacture, shipping or fitting.
(e)    And - of course, the possibility of bad design!!

In the next post I will publish a simple test that is very easy to do, and is specific to inset stoves.

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Blacksmith Artisan and Inset Stove Design Part 1

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How an Inset Stove

Should Work - part 1

Some concern about the functioning of a friends Blacksmith Artisan inset stove has sparked this series of posts concerning the design, efficiency, and function of inset stoves generally.

Above is a diagram of a typical inset stove. An inset stove is essentially two boxes - one inside the other. 

TWO BOXES

(1) THE INNER OR FIRE BOX

The inner box is the "Fire Box" in which the fire burns. It usually has two air supplies, a primary air supply which allows air to come in underneath the fire, and a secondary air supply which allows air in above the fire. In some designs the secondary air is arranged so as it acts as an air wash to keep the door glass cleaner by wafting the combustion fumes away from the glass.

(2) THE OUTER BOX

The outer casing forms the "Convection Heating System". It is absolutely vital that the air in the "Convection System"  DOES NOT MIX IN ANY WAY with the air used for combustion. If it does mix, at the least it will cause the stove to be very inefficient, and at the worst, it may allow noxious fumes into the room. 

Possible causes which might allow the two air flows to mix are:

(1) a crack in the casing, or 

(2) poorly sealed joints, or 

(3) bad design.

WARNING 

COMBUSTION AIR AND CONVECTION AIR 

SHOULD NOT MIX

The Vital and Distinguishing Part of an Inset Stove

The distinguishing and vital part of an inset stove - and clearly different from a free-standing stove, is the outer "Box" or "convection airway" which causes air to circulate in and around the back, sides, and top of the inner box or "Fire Box" - thus carrying the heat from these surfaces out into the room.. 

Without a properly functioning convection system, an inset stove would be no better than a simple door on a fireplace, as the heat from the back, sides and top of the stove would simply be lost up the chimney..

TWO SEPERATE AIR SYSTEMS

How should the air flow systems work in an "Inset Stove"?  

First point to remember is that there are -  2 -  TWO DISTINCT AIR FLOW SYSTEMS to consider. The FIRST rule is that these two air flows should not mix.

I will write further on this very soon. Look out for the next post on this subject.

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