Heating with Wood: Stoves, Firewood and Safety

Wood is the most practical primary heat source for many cabins, homesteads and rural homes in Canada and the northern United States. Done properly, it is clean, efficient and safe. Done badly, it wastes fuel, fills the chimney with creosote and causes house fires. This guide covers choosing and sizing a stove, clearances and chimneys, firewood energy and seasoning, how much wood a winter takes, burning practice, maintenance, alarms and insurance.

Stove types

Certified wood stoves

Modern stoves are tested for smoke emissions. In Canada, the standard is CSA B415.1. In the United States, wood heaters sold since May 2020 must meet the EPA limit of 2.0 g of particulate per hour (or 2.5 g/h when tested with cordwood). Older uncertified stoves commonly emit 15 to 30 g/h or more. A certified stove burns far cleaner and usually uses less wood for the same heat.

Many jurisdictions restrict uncertified stoves. British Columbia regulates the sale of solid-fuel appliances, and some local governments require uncertified stoves to be removed, for example when a property is sold. Check local bylaws before buying or keeping an older stove.

Catalytic and non-catalytic stoves

Catalytic stoves pass smoke through a coated honeycomb that lets the gases burn at about 260 °C (500 °F), far lower than otherwise needed. They burn cleanly at low, steady output, which suits long overnight burns. The catalyst typically lasts 10,000 to 12,000 hours and must then be replaced. The bypass damper is opened for loading and start-up and closed once the catalyst is active.

Non-catalytic stoves use an insulated firebox, a baffle and pre-heated secondary air through perforated tubes to burn the gases above the fire. They are simpler, with fewer parts to replace, but burn cleanly over a narrower range and run less well at very low output.

Hybrid stoves combine both systems.

Cookstoves

A wood cookstove has an oven and cooking surface heated by the firebox. Certification rules for cookstoves differ from those for heating stoves; some models are certified and some are not. Cookstoves need smaller, more frequent loads and usually larger clearances than heating stoves.

Masonry heaters

A masonry heater burns a large load of wood quickly and very hot, usually once or twice a day, then passes the hot gases through long masonry channels. The masonry, which by definition in ASTM E1602 weighs at least 800 kg (1,760 lb), stores the heat and releases it to the room over 12 to 24 hours. Combustion is clean because the fire is never damped down. Masonry heaters are expensive and need a foundation designed for their weight.

Sizing a stove

Manufacturers' heating-area ratings assume average insulation and climate and are a rough guide only. A better method starts from the building's heat loss at the coldest expected outdoor temperature, called the design heat load.

The table shows January design temperatures and annual heating degree-days for some Canadian locations from the National Building Code climate data. Look up your own location in the code tables.

A heat-loss calculation by an energy advisor or software gives the building's heat-loss rate in watts per degree of inside-outside temperature difference. Multiply by the design temperature difference to get the design load.

Installation clearances

A listed stove has been safety-tested (to ULC-S627 in Canada or UL 1482 in the US), and its label states minimum distances to combustibles such as wood framing, drywall over studs and furniture. Those listed clearances govern; for modern stoves they are often 300 to 450 mm (12 to 18 in) at the back and sides.

An unlisted stove, or one with a missing label, must use the installation code's default clearances, typically 900 mm (36 in) or more on all sides. The code is CSA B365 in Canada and NFPA 211 in the US. Many insurers will not cover an unlisted stove.

• Floor protection: place the stove on a non-combustible floor pad of the size and type stated in the manual. Typical requirements are 450 mm (18 in) in front of the loading door in Canada, or 406 mm (16 in) in the US, and 200 mm (8 in) at the sides and back.
• Single-wall stovepipe: keep at least 450 mm (18 in) from combustibles unless a listed shield or double-wall connector allows less.
• Clearance reduction: listed shields, or a non-combustible panel with a ventilated air gap of at least 25 mm (1 in), reduce clearances by amounts set in the code. Tile or brick fixed directly to a wall is not a heat shield.

Stovepipe (connector) basics

• Keep it short, with no more than two 90° elbows.
• Slope any horizontal run upward toward the chimney by at least 20 mm per metre (1/4 in per foot).
• Point each crimped end down toward the stove so creosote runs back inside.
• Fasten each joint with three sheet-metal screws.
• Never pass stovepipe through a wall, ceiling or floor; use a listed chimney section or pass-through.

Chimney basics

The chimney creates the draft that pulls air into the stove. Most new installations use factory-built insulated stainless chimney, often called Class A. In Canada it must be listed to ULC-S629; in the US the equivalent is UL 103HT. Install it with the manufacturer's listed ceiling supports, firestops, roof flashing and storm collar, and keep it at its listed clearance from combustibles, which is commonly 50 mm (2 in).

Masonry chimneys need an intact flue liner of the correct size; cracked or missing liners are a common cause of house fires.

The 3-2-10 rule

The chimney must extend:

• at least 0.9 m (3 ft) above the highest point where it passes through the roof, and
• at least 0.6 m (2 ft) higher than any part of the building within 3 m (10 ft) horizontally.

On a steep roof, the second requirement usually governs.

Firewood

Measuring firewood

A full cord is a stack 1.2 m × 1.2 m × 2.4 m (4 ft × 4 ft × 8 ft): 128 cu ft or 3.62 m³. Allowing for air spaces, it holds about 2.4 m³ (85 cu ft) of solid wood. In Canada, firewood must be sold by the cord or the stacked cubic metre. Terms such as "face cord", "rick" or "truckload" have no fixed volume; a face cord of 400 mm (16 in) pieces is one-third of a cord.

Energy by species

Dry wood of almost every species holds about 20 MJ per kilogram. What differs is density: a cord of dense hardwood weighs, and holds, much more than a cord of softwood.

The table estimates gross energy per cord from each species' specific gravity, assuming 2.4 m³ of solid wood per cord and 20 MJ/kg. Values are approximate, roughly ±10%, and vary with growing conditions and how tightly the wood is stacked.

Dry softwoods are safe to burn; they burn faster and suit spring and fall fires. Hardwoods give longer burns in cold weather.

Seasoning and moisture

Freshly cut wood commonly measures 40% moisture or more. Burn wood only below 20%. Wet wood burns cool and smoky, builds creosote and delivers less heat.

Evaporating the extra water costs some energy directly. For a cord of paper birch (1,152 kg dry), wood at 50% moisture holds 576 kg of water and wood at 20% holds 230 kg, a difference of 346 kg. At about 2.6 MJ to heat and evaporate each kilogram, that is 346 × 2.6 = about 900 MJ, or about 4% of the cord's energy. The larger loss is that a cool, smouldering fire sends unburned fuel up the chimney as smoke and creosote.

• Cut and split soon after felling; wood dries mainly through cut ends and split faces.
• Stack off the ground in single rows, in sun and wind, top covered and sides open.
• Most species dry in 6 to 12 months stacked this way through a summer; oak may need 18 to 24 months.

Using a moisture meter

A pin-type moisture meter removes the guesswork. Bring a piece to room temperature, split it, and push the pins into the freshly split face, parallel to the grain. Readings from the outside of a split or a cold piece are misleadingly low. Test several pieces.

How much wood for a winter

Annual heat demand can be estimated from the heat-loss rate and your location's heating degree-days.

Annual heat (Wh) = heat-loss rate (W/°C) × heating degree-days × 24 hours

Wet wood, an old stove or poor burning habits can double real use. Record what you burn each winter and use that to plan the next.

Burning practice

Top-down fires

A top-down fire burns cleanly from the start because smoke from the wood below passes through the flames above.

1. Place three or four larger splits on the bottom, close together.
2. Lay a layer of smaller splits across them, then a layer of kindling.
3. Put fire starter or crumpled newspaper on top, with a little fine kindling.
4. Open the air control fully, light the top, and close the door.

Reloading and avoiding smoulder

• Reload onto hot coals raked toward the air inlet.
• Keep the air control open for 15 to 30 minutes after loading, until the new wood is charred black and burning well. Only then turn it down in steps.
• Never shut the air down on a full load of fresh wood to make it last overnight. That produces the heaviest smoke and creosote. Use dense hardwood and a moderate setting for long burns instead.
• Use a stovepipe or flue thermometer. On single-wall pipe, typical surface readings for a good burn are about 120 to 245 °C (250 to 475 °F); follow the thermometer maker's ranges.
• Check the chimney top from outside. After start-up, the exhaust should be clear or white steam. Grey or blue smoke means the fire needs more air or the wood is wet.

Creosote and chimney sweeping

Creosote forms when smoke condenses on cool chimney walls, as flaky soot, crunchy tar-like flakes or a hard, shiny glaze. All three burn, and a chimney fire can crack liners, damage factory-built chimney and ignite framing.

• Inspect the chimney and stovepipe at least yearly, and monthly in the first season with a new stove or wood supply.
• Sweep when deposits reach about 3 mm (1/8 in) thick anywhere in the system, and at least once a year whether or not they have.
• Check the chimney cap screen, which can plug with creosote and choke the draft.
• Have glazed creosote removed by a professional sweep.

Carbon monoxide and smoke alarms

Carbon monoxide (CO) is a colourless, odourless gas from incomplete combustion. A stove can release it through a cracked body, leaking connector, blocked chimney, or reverse draft caused by exhaust fans in a tight house.

• CO alarms: install them near every sleeping area and on each level with a fuel-burning appliance. Use alarms certified to CSA 6.19 in Canada or UL 2034 in the US. Many provinces and states require CO alarms in homes with a fuel-burning appliance; BC and Ontario are among them.
• Smoke alarms: install them on every level and outside every sleeping area, certified to CAN/ULC-S531 or UL 217. Test them monthly.
• Replace CO and smoke alarms at the end of the life stated by the manufacturer, typically 7 to 10 years. On off-grid or intermittent power, use alarms with sealed long-life batteries or battery backup.
• Keep a multipurpose fire extinguisher, rated at least 2-A:10-B:C, near the stove and near the exit.

CO poisoning causes headache, dizziness, nausea and confusion, often in several people or pets at once. If an alarm sounds or anyone has symptoms, get everyone outside and call 911.

Inspection and insurance

Tell your insurer about any wood-burning appliance before you use it; an undisclosed stove can be grounds for refusing a claim.

In Canada, the usual proof is an inspection by a technician certified by WETT (Wood Energy Technology Transfer). WETT-certified inspectors check the appliance, clearances, floor protection, connector and chimney against the manufacturer's instructions and CSA B365, and provide a written report, often requested by insurers and buyers. In the US, look for an inspection to NFPA 211 by a chimney professional certified by the Chimney Safety Institute of America (CSIA).

Some insurers charge more for wood heat, decline unlisted or homemade stoves, or require sweeping records. Keep the manual, inspection report and dated sweeping receipts together.

Key points

• Use a stove certified to CSA B415.1 or EPA standards, and check local bylaws on older stoves.
• Size the stove to the house's design heat load. Oversized stoves smoulder and build creosote.
• Follow the listed clearances on the stove label, use insulated chimney listed to ULC-S629 or UL 103HT, and meet the 3-2-10 rule.
• A cord is 3.62 m³ (128 cu ft) stacked. Dense hardwood holds nearly twice the energy of the lightest softwoods.
• Burn only wood below 20% moisture, confirmed with a moisture meter on a freshly split face.
• Inspect the chimney at least annually and sweep at 3 mm (1/8 in) of buildup.
• Install CO and smoke alarms, store ashes in a lidded metal container outdoors, and get a WETT inspection for insurance in Canada.

This guide is general information. Codes, permits and safety requirements vary by province, state and municipality. Check local rules and use a qualified professional for electrical, gas, chimney and septic work where required.

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