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Obtaining Domestic Hot Water from a Wood or Coal Stove

Many folks have expressed a desire to obtain hot water from their stoves. First, I should mention that this article refers to Domestic Hot Water, meaning the water that is used to wash dishes, take showers, etc. A woodstove cannot produce the volumes of water needed to heat your home through a baseboard or radiator system. If you are looking to heat your entire home AND produce your Domestic Hot Water, take a look at some of the wood burning central heating systems. These produce your hot water AND heat your home!

There are two different types of heat exchangers which can be fitted to stoves and used to heat your domestic water.

1. External Heat exchangers - if the stove has a large flat surface on the rear, then a serpentine can be fabricated that goes against the rear. If it is enclosed with a layer of sheet metal behind this coil, it will provide better heat. I’ve had them custom made..but the same shops that make DHW coils (tankless heater) for hot water boilers. These coils were made from a finned copper (usually 3/4”), so much the better for heat exchange. You could make your own by using 180 degree copper bends, but use high-temp (silver) solder so the coils don’t come apart if they ever hit a very high temperature.This would only happen if they ran out of water and the stove was VERY hot. Input would be into the bottom of the coil, and output from the top. A pressure relief valve should be installed next to the coil…WITH NO VALVES BETWEEN THIS PRESSURE RELIEF VALVE AND THE COIL.

2. Internal Heat Exchangers - A few companies make such an item, although it may not be easy to find. The best ones are small tanks or coils made of stainless steel. The kits come with instructions and a pressure relief valve. In order to install an internal heat exchanger, a hole must be drilled into the stove body. This may be a job for a professional, as you don’t want to compromise the safety or integrity of your...
Central Heating with Wood, Coal or Pellets (note: this article covers INDOOR approved central heating systems and does not address the Outdoor Wood Boilers (OWBs). See this article for more on OWBs.

Central heating has been with us for thousands of years. In fact, cities in the Roman Empire heated many public building and baths by conducting heat from a wood fire up through empty spaces under the floors.

After the fall of the Roman Empire, things actually went backwards, and early Americans 1,700 hundred years later were still using open fireplaces and vast quantities of wood to stay warm—well, actually to stay cold! It took a new revolution started by Ben Franklin (who redesigned cast-iron stoves) to finally bring some decent heating appliances to our American ancestors.

Fast forward to the late 1800s and a new fuel was discovered: Clean burning hard coal (anthracite) became the fuel of choice for a nation on the move. The old stoves were junked and coal-fired central heat was installed in virtually every home and commercial building. This continued until after WWII, when most coal units were replaced over time by oil or gas-fired boilers and furnaces.

Now we are in the midst of the “modern” stove movement, and it appears a lot of folks have forgotten about one of the BEST options for using alternative fuels: clean and comfortable Central Heat—controlled by a thermostat!

Stay warm and comfortable with Central Heating Products by Alternative Heating of North America. Our products range from high efficiency indoor residential boilers to outdoor and commercial units. Accessories include plate heat exchangers, Danfoss themostatic valves and more. Declare your Energy Independence now. Dealer inquires invited!...
Central Heat with Coal

Coal Stoker Fire (efm)

Hard coal (anthracite) can be an economical fuel and is in ready supply within a couple hundred miles of the Pennsylvania Coal fields. For some reading on space heating coal stoves, see this article. Check out our Fuel Comparison Calculator to compare the cost of Anthracite coal to other home heating options.

Coal is well suited to central heat because of the long burn times, clean burn characteristics and the ability to easily burn at a range of outputs. As with other central heating equipment, coal units are available for Hot Water (boiler) and Hot Air (furnaces). Note that a boiler can be tied into a hot air system using a fan coil, but a furnace cannot be tied into a boiler system.

Types of Systems

Coal central heaters are available in hand-fed or stoker models.


EFM Coal Stoker Furnace

A hand fed (also called batch fed) unit is similar to a freestanding coal stove, where the operator loads the coal into the unit using a shovel or coal bucket. The coal burns in one large mass - usually using the natural draft of the chimney, and the heat is exchanged into your existing distribution system. Hand fed models will usually use “nut” coal or larger. These larger sizes allow for air to easily come up through the large batch of coal. A typical mid-size hand fed unit will hold 70 pounds of coal, and require approx 2 feedings every 24 hours (12 hour burn time).

A Coal Stoker is a automatic system, using a screw auger to feed very small coal (rice size) into a burn pot. The stoker can be fed from a large bin holding many tons of coal. Most stokers on the market today are boilers (water based), although a few companies (EFM) produce hot air models.

Shopping for a Coal Central System

Make certain that the...
Written by Eric Johnson and Craig Issod

Outdoor Wood Boilers, also called OWBs or Outdoor Wood Burners, consist of a firebox surrounded by a water jacket and a control system all housed in an insulated, steel-sided enclosure with a roof. Hot water is circulated through insulated, underground piping between the boiler and the house. OWBs have become very popular in many rural areas of the United States, with substantial sales in the Northeast and Midwest, where hardwood is plentiful and winters are long and cold.

OWB Typical Setup

Source: HPBA

Although typically referred to as “boilers,” OWBs are not boilers in the traditional sense. In a conventional indoor boiler (oil, gas, wood or coal hydronic heater), water is heated in a pressurized vessel and then circulated through the heating system. In an OWB, the water is open to the atmosphere and thus, not pressurized. This allows the OWB to be built to different standards than a traditional indoor boiler, and makes it exempt from some of the regulations that apply to pressurized heating appliances.

There are pros and cons to consider when shopping for an OWB. One of the advantages of open systems is that they are safer than pressurized boilers. And because they’re usually sited away from the house and other buildings on the property, they dont affect your homeowners insurance rates. All the creosote, smoke, ash, wood storage, etc. are outside of the house as well, which is appealing to many people familiar with wood stoves. And they can burn much bigger pieces of wood than a stove.


improper burning in an OWB

On the down side, open systems are prone to corrosion and the accumulation of debris in the system, which can be a maintenance concern. Overall system efficiency is a problem with OWBs as well, since it is virtually impossible to efficiently burn wood in a firebox surrounded by water. The result is smoke, which is basically unused...
Pellet and Corn Furnaces and Boilers


Over the past decade, a quiet revolution has been taking place in Europe and in certain parts of North America, centering on the use of locally-produced wood pellets and corn or corn/pellet mixtures for residential central heat. The increasing popularity of these heaters is largely being driven by high fossil fuel costs, although the perception that these fuels are “green” and renewable is also a factor for some consumers. However the fact remains that until the very recent sharp increases in the price of oil and LP, alternative fuel central heating systems were not in high demand on this side of the Atlantic.

As with chunk firewood and coal, central heating with refined fuels such as wood pellets and shelled corn has a number of advantages over space or “spot” heat typically produced by stoves. It allows the entire house to be heated evenly and respond to the settings of a wall thermostat. The heat can be zoned, allowing for different areas of the house to be heated on demand. Domestic hot water (DHW) can be produced as well, providing additional savings. Central heat also keeps most of the mess and dust of solid fuel in the basement, utility room or outbuilding.

The new generation of pellet/corn appliances is available in both hot air configurations (furnaces) or hot water (boiler) models. All use automatic feeding systems, either from a built-in hopper or an external bin. Typical maximum outputs range from 50,000 to 100,000 BTU (14 to 28 KW) per hour, enough to satisfy most residential heating needs.

Is a pellet or corn furnace or boiler right for you?

An add-on central heating appliance represents a substantial investment, usually costing from $6,000 (hot air) to $12,000 (hot water) for an installed system. Although mostly automatic, you will have to deal with buying fuel, loading pellets into the hopper or bin, removing the ash and general service and maintenance. And you should...
Water storage can be a great addition to a wood or pellet boiler system, however you must plan the system well in order to gain the maximum advantage. You can use the calculator below to get a rough idea of how much water storage you might need to achieve your goals.
*Maximum temperature of storage
170 180 190
*Lowest temp of storage
110 120 130 140 150 160
*Gallons of Storage
120 240 400 600 800
If you planned well, you now can build the perfect system to suit your needs and get even more comfort from your renewable biomass fuel.
DIscussion of Storage and Storage Tanks..... Note, you can find a vast array of information on our Boiler Room Forum - and even get your personal questions answered! Here are some specific Boiler Room links:
Pressurized Storage Control by Nofossil

Let's start with the basics of combustion and wood burnings. Wood burns cleanest and most efficient when burning very hot! For that reason, many of the new downdraft ceramic base (also called gasifiers) boilers are designed to only burn at very high rates - often higher than what is needed to heat the home. As a result, such a system will turn itself off when the house is up to temperature and the water in the boiler reaches it's set point (usually 180-190 degrees F). This so-called idle mode produces vapors and liquids which are corrosive to the boiler and may also result in more smoke and creosote in the chimney system.

Since the weather and heat load differ daily, it is virtually impossible to accurately size a wood boiler for all winter conditions. At many times the boiler will be too big - and at some times it may even struggle to keep up with a very heavy heating and DHW load. These are cases where large water storage systems can help.
A water storage system takes any excess output of the boiler and stores it in water tanks. Then, when this heat is needed, it can be drawn...
Troubleshooting Direct Vent Products
Like Flying into the Bermuda Triangle!

By Ken Rajesky
Note: This article is technical in nature and intended for mechanics who are knowledgeable regarding the service and operation of gas and hearth appliances.

The call comes in from a longtime customer - his year-old direct vent starts up but within minutes the flames disappear. Your chest tightens because you know that severe weather is heading your way and his stove will be a major source of heat should the power go out. Your service guy is straight out with new installations and other service calls. And, if you leave the shop, it may take hours to solve his problem because you are just not sure about troubleshooting direct vented products. So, what do you? The answer is education.


Direct vented products are not the mystery that many service people feel they are. First, what is a direct vented product? Direct vented products are basically sealed systems. That means that combustion air is provided via a sealed intake duct. A separately sealed channel evacuates exhausts from the product. You may a vent system that has the exhaust channel within the combustion air channel. This is called a co-axial vent. Or, you may have two fully separate, sealed channels. A third option is a system that uses both a co-axial and co-linear system. Regardless of which system is used, the product must breathe in, and breathe out. If the product cannot breathe in, it will not have sufficient oxygen to sustain combustion. If the product cannot breathe out, the newly developed exhausts will contaminate the combustion zone not allowing combustion to continue. The advantage of direct vented products is that they are installation flexible, and supply their own combustion air. Another advantage of direct vented products is that they are unaffected by home negative pressures that may cause exhaust...