In the other Fire pages we learn about how fire burns, how to build fires, what to use as fire starters, fuels, and where to burn fires out doors. Survival is not limited to what we might do outdoors, though. At some point we will get to our BOL. Some time in the future we should expect to improve the BOL.

There will come a time when we switch from survival to homesteading. Let us now look at appliances for heating the BOL and the homestead.

Fireplaces

Fireplaces are considered decorative appliances by many local authorities. Fireplaces have been used throughout history as heating appliances. Their efficiency as heaters varies greatly based upon their construction and location in the home. Fireplaces built inside the house envelope are much more efficient heaters than those built on the exterior side of the envelope. Those built outside the envelope are the least efficient at heating. Another factor contributing to the heating efficiency of a fireplace is the combustion efficiency. Most folks use a firelay that is only 17% combustion efficiency. The Top Down firelay has a combustion efficiency of 80% for the initial charge of wood.

Brick fireplace
Brick fireplaces are composed of multiple chambers. The inner chamber is the firebox. It is usually built using firebrick, although, older fireplaces might be built of redbrick. The other chamber should be separated by 2 to 4 inches of air space from the firebox and can be built using any masonry units (redbrick, cinder block, stone). The chamber above the firebox is the smoke chamber which can be thought of as a funnel to guide the exhaust products to the flue.

Brick fireplace side walls usually taper toward the read wall. The rear wall may have a break point where it begins to slant forward and upward. The idea for these slanting walls is to reflect or refract more heat into the room.

The smoke chamber and the firebox are usually separated by a damper. The primary function of a damper is to curb the flow of cold air from the flue when the fireplace is not in use. Some people use the damper as a way to control how fast a fire burns. In practice this is the less preferred method since it deprives the fire of combustion air. A better method would be to control how much fuel is added.

Rumford fireplace
In 1776 the Count of Rumford performed exhaustive study on fireplace design. He derived a set of ratios to govern the size and shape of a fireplace. While the typical masonry fireplace is generally built approaching the golden rectangle, the Rumford ratios approximate parabolas and are taller than they are wide. There are other details particular to the Rumford design.

Learn More - Design

Masonry Heaters
A masonry heater is a massive block of masonry designed in such a way as to extract the majority of heat from the fire in the firebox. The firebox is typically very small. For the “smoke chamber” a masonry fireplace has a serpentine pathway that leads to the flue. The flue may be above the firebox but is usually several feet off to the side. The serpentine chamber is built in such a way to provide access for cleaning.
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Rocket Mass Heater
This heater combines the best features of an EPA wood stove and a Masonry Heater. The basic design is that of a Dakota Fire Hole (See Building Fires). However, one must see this as three or four generations of improvement later. The combustion riser, located inside the steel drum, brings the un-burnt gasses up for secondary combustion. The combustion is nearly 100% efficient. The bench that wraps that corner has a serpentine duct which conducts the last of the combustion by-product to the outside. From what I can tell, those are CO2 and water vapor. The terminal temperature is about 90° F. Like the masonry heater, the mass of masonry absorbs and radiates the heat over a long period. Also similar to the masonry heater this appliance uses only a small charge of wood to provide a days worth of heat. One builder/owner reports that wher he used 4 cords of wood to heat his home with an EPA wood stove, he now only uses only 1/2 cord of wood.
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Factory Built

Modern technology has brought onto the scene factory built fireplaces. These are engineered to utilize air space, fire location, and refractories to achieve very close clearances to combustible materials. They are often referred to as zero-clearance fireplaces because at the very front of the appliance combustible material can actually touch the appliance. Where masonry fireplaces have clearances dictated by building code (cf. NFPA211, IRC) factory built fireplace must adhere to Underwriter’s Laboratory standards and thus their clearances are stipulated by each manufacturer for each model.

Stoves

Basic
A basic stove is an appliance which contains the fire and radiates heat through its surfaces to the area around it. The masonry heater above fits this definition, however, it is not what we think of when we use the word stove.

Wood burning Stoves
Wood burning stoves have mutated quite a lot over the past 50 years. In days of yore a wood stove would have been a barrel shaped affair made of cast iron parts. In the 1970’s many people re-tasked steel oil barrels as wood stoves. In the late 1970’s many manufacturers appeared making wood stoves from steel plate. Some time in the 1980’s pollution control brought on the use of catalytic combustors to promote higher combustion efficiency. Catalytic combustors have the drawback of having a light off temperature and so do not work until that temperature is achieved. The catalytic package is fragile and has a tedency to get clogged. Very few people knew that the package needed maintenance. In the first decade of the 2000’s efficiency began to be achieved through the introduction of secondary combustion air instead of catalysts. This is a low maintenance way to achieve 75% combustion efficiency.

Coal Stoves
Coal stoves follow most of the design features as woodstoves. The main difference is the use of a shaker grate to allow ash and clinkers to fall out of the fire. Shaker grates are operated manually.

Pellet Stoves
Pellet stoves use a pelletized fuel composed of wood products. These stoves achieve up to 85% combustion efficiency through the use of mechanically metered fuel feed and uniformity of fuel size. Other fuels that are fairly uniform in size such as corn, wheat, and cherry pits are sometimes used. Non-wood fuels have certain drawbacks and are generally not permitted by the manufacturer. For instance the exhaust products from corn are excessively acidic and lead to early appliance failure.



Gas Stoves
Whether natural gas or propane (liquid petroleum), gas is a popular fuel for stoves. Obviously, the design of a gas stove precludes the use of other fuels (there are a few hybrid models out there now). Gas stoves have good combustion efficiency.
Oil Stoves
Oil stoves are very rare. They are prohibited by the NFPA211

Jet Stove
A jet stove is an appliance that utilizes a constricted firebox and flue to achieve high temperatures from a small amount of fuel through rapid combustion. The action of a jet stove is comparable to the the action in a ram jet. The Internet is full of examples using various fuels. The size of jet stoves tends to be small, on the scale of a camp stove. Some experimenters have built jet stoves using masonry materials with sizes on the scale of a household fireplace.

Furnaces and Boilers

Furnaces are appliances having heat exchanges that are designed to deliver heated air through ductwork to various parts of the house. Boilers are similar except they deliver heated water through pipes to heat exchangers (radiators) located away from the appliance. These centralized appliances provide a uniform temperature to the whole house. For greater cost efficiency many homes have zone heating which diverts the heated fluid away from some parts of the house when those parts are not in use.

Furnaces and boilers are available which use all the aforementioned fuels. There are some hybrids, however, solid fuel burning furnaces/boilers must each have their own flue. Fluid burning appliance may share a single flue.

Chimneys and Vents

Chimneys and vents are like squares and rectangles. All chimneys are vents, but not all vents are chimneys. Chimneys and vents are available in a variety of materials. Nearly all combustion appliances use a vent or a chimney. The exception is “vent free” gas burning appliances. Such appliances do not require venting because their combustion efficiency is high enough that minimal amounts of carbon monoxide (CO) are emitted. Mis-arrangement of burner media (logs, glowing embers, burner sand) will contribute to less than ideal combustion efficiency and higher amounts of CO. All combustion appliances include CO2 and water vapor as by-products of combustion.

Chimneys’ flues are sized according to the appliance(s) they will serve. For fireplaces the flue will be 1/8th to 1/12th the size of the fireplace opening depending on the cross sectional shape of the flue. For stoves and furnaces the flue collar where the smoke exhausts from the appliance is what determines the flue size. This assumes that the manufacturer has tested the appliance for needed draft. Learn more about chimney physics and design on this page about Chimney Physics.

Masonry
Masonry chimney’s are comprised of a masonry shell enclosing a flue, or a vertical passage. Since 1905 building code has required that the flue be lined. Lining at that time was considered to be firebrick or aqueous terracotta tile. Modern flues are usually lined with terracotta tile, although stainless steel is often used. Stainless steel liners can be used from the initial build but are most often used as a replacement when the terracotta has failed. Another type of liner is cast refractory. Masonry chimneys have a clearance of 2” from combustible materials. This clearance is seldom observed in attic areas or at the roof line.




Stovepipe
Single wall stove pipe has been used as both an appliance connector and as a chimney. Modern code does not permit stovepipe to be used as a chimney. It would be unwise for anyone to attempt to use stovepipe as a chimney since it can not bear the heat and corrosive environment. Further stovepipe has no insulative quality. As an appliance connector stove pipe has a clearance of 18 inches to combustible material. There are double wall connectors available with clearances as low as 6”

Class A
Class A chimney is suitable for all fuels. It is comprised of multiple metal walls*. Usually there are 3 walls, though I have seen Class A chimeny with as few as 2 walls and as many as four walls. Some designs have nothing but air between the walls. Some designs use ceramic blanket between the inner and middle walls. Those with only air chambers utilize a thermo-siphon to carry excess heat to the outer atmosphere. They are prone to warping and buckling during chimney fires. Those with ceramic blanket also have air insulation, though seldom have a thermo-siphon. They are more likely to survive a chimney fire without warping or buckling.





About vents
Vents are used for combustion appliances that extract greater amounts of heat and thus have cooler exhaust gasses. B-Vent is often used for high efficiency gas burning appliances. L-Vent might be used for high efficiency oil burning appliances. Both are multi-wall pipe. Neither is considered chimney.

Gas burning appliances are available as “direct vent”. This venting may be a double wall metal pipe where combustion air is drawn to the appliance between the inner and outer walls. This both warms the combustion air and insulates the vent from nearby combustible material. Some gas burning furnaces and boilers have heat extraction to such a great degree that their exhaust gasses are vented through PVC pipe.
Pellet stoves may be vented using L-Vent but are usually installed using pellet vent. Pellet vent has features, such as gasketed joints, that are not found in L-Vent.

*Very old Class A chimney was once made with castable refractory material. There are no longer any manufacturers for this design.

by: Zee-Man

Related Pages:
About Fire , Firewood , Fire Starting , Fire Places , Alternative Fire Starters, Heating Appliances