In America, the first wood heating devices in the historic era were large open fireplaces. To this were added wood fired ovens, some on the back wall of the fireplace and some to the side of the fireplace. In the middle to late eighteen hundreds cast iron cookstoves were invented. The classic six-lid cookstove could have one or both lids plus the divider over the firebox removed and stepped cast iron pots and griddles could be placed tightly but directly over the fire. One can still find some of these old stepped pots including large cast iron tea kettles.
Eventually, an extension to one side of the cookstove was added with a tin lined copper reservoir for heating domestic hot water. Water was poured into the reservoir with pails and could be drawn out of the reservoir with a long handled pan or through a small brass spigot in the front of the stove coming through the reservoir and castings.
Our Norridgewock, Maine farmhouse, built in the l830’s, boasted the first year round running water system in the area. A spring on the bank near the house was tapped with a pipe which ran down a hill to a hydraulic ram and pressure building up inside the bell shaped ram allowed the water to be forced back uphill in a smaller diameter pipe to an oak barrel in the kitchen. An overflow pipe ran out of the top of the barrel back to a safe dump zone outdoors. In the right light you can still see the small blocks of wood in the wide board wainscoting where the old pipes came and went. Twenty or more years ago, a woman in her sixties or seventies came to the door once who had lived in the house as a girl and she was able to describe in detail exactly where the barrel had stood which confirmed all of our detective work.
This system meant that the house had fresh water in the kitchen all year long in a never-ending stream, but this system only brought the water into the house. It did not heat the water or move it to the cookstove. The next breakthrough in hot water design came with the invention of a brass water coil for the inside of the cookstove firebox linked to a thirty gallon hot water tank on a stand next to the cookstove and a running water supply keeping the tank and water jacket full. Copper tanks without insulation almost never overheated as they could radiate more and more heat from their surface as the firebox heat in the stove increased in intensity or duration. These systems delivered hot water very effectively without safety valves to any part of the house that had plumbing.
I used to go to a hardware store in Skowhegan, Maine that still had l80 degree threaded brass elbows designed for fabricating the brass water jackets. A photo of water jackets we’ve used is shown below.
When we experimented with a variety of more “modern” cookstoves, including the Waterford, Stanley from Ireland, the Stanley included a domestic hot jacket option that sat in the rear of the firebox and many customers chose to include this option in their Stanley purchases. For many years, Maine Wood Heat was the North American importer of an Austrian built cookstove with a very large water jacket that completely surrounded the fire. The Austrian Tirolia had insulated sides and rear and top and an insulated lid so it could be used even during the summer for short burns. In one hour, we could heat an eighty gallon domestic hot water tank with a gravity thermosyphon loop going to the tank upstairs. We had an aquastat (water thermostat) in the tank that allowed the tank to get to the desired “high limit” that we had set, and then it automatically forced the house radiator circulator pump to go on. Whenever the domestic tank got low in heat, the next batch of hot water production always went first to the tank and then to the house radiators. We cooked, baked, heated domestic hot water and the house for years using this central heating cookstove. We still have people calling us who have had their Tirolias in use for twenty years or more.
The Austrian company ultimately went out of business and we also decided to stop selling them when we realized that we needed to make a choice between a low emissions system like a masonry heater, versus a higher emissions system like a water clad firebox of the Tirolia. Once we switched our focus entirely to masonry heaters, the interest from the public in heating domestic hot water or radiators from the systems we were building did not cease. In the very early days of masonry heaters in Maine in the late 1970’s, I remember a heater built near the State Capitol of Augusta that someone had run large diameter hot water pipes throughout the system thinking that if a little bit works then bigger would be much better. In the first year of operation, a leak somewhere in the system had destroyed everything. Steam of course has explosive force and is highly dangerous and any inclusion of water in a masonry system has to be carefully designed and understood and executed. Over time we found that we could build modest sized stainless steel heat exchangers and place them directly in the fire of a brick wood cookstove and get good results, albeit with a dirtier burn than a firebox without a water jacket. We also found that if we put a stainless steel water jacket in a non-direct or “remote” location behind a layer of firebrick in the throat area of our heaters, we could get a trickle charge gain on domestic hot water production without lowering combustion efficiency. Other people have developed different systems which have done a similar job of modest domestic hot water production. In one or more instances we designed water jackets that were made of a copper tubing layout on top of the inner capping slabs. We designed but did not build the idea of such an array inside a stainless tray on top of the capping slabs with the tubing surrounded by glass beads or marbles or stainless steel or steel shot and to get better conductivity to the copper tubing. All such designs called for installing a large domestic hot water tank on the next floor level directly above the heater and/or cooker guaranteeing a thermosyphon non-electric transfer of heat to the tank.
In the event of a power outage such a set up guarantees that there will be no overheating of the coil or hot water tank because of its large capacity. We have always discouraged the use of any domestic water jacket system coupled to a tank located below the heater and requiring a pump for its safe operation. In New Zealand, it became very clear to Albie that New Zealanders want to heat hot water from whatever wood burning appliance they are using. In the home that Albie stayed in with Chris and Debbie Naylor, there was a blue enameled stove in the kitchen with a refractory lined firebox, and a horizontal baffle above the firebox. At the throat of the baffle was a stainless steel secondary air tube for more complete combustion and at the rear of the firebox secondary chamber was a domestic hot water jacket, which in New Zealand is called a “wetback.”
Sampsa plans to have some solar panels for domestic hot water in his house design but he also wanted to heat some hot water from his masonry heater and he wanted it to not only heat domestic hot water, but to also send heat to a large room on a level below the heater and to a bathroom two partition walls beyond the heater. This is why the heater is being built in the lounge, which you can see in the house plan above. It is very common in Germany to have cast iron and firebrick central heating boilers built inside of ceramic tile Kachelofens. This puts a traditional radiant mass heater in a central living room in the house but also sends heat to a number of remote rooms and also likely can produce domestic hot water. It is unlikely that such central heating Kachelofen burn with the efficiency or cleanliness of a standard non-water jacketed “Grundofen.”
In Finland, Sampsa found a company that made a cast iron heat exchanger that eliminated the presence of hot water entirely from the heater itself. Instead, the system he found replaced the top capping slabs of castable refractory with two “needled” plates of overlapping cast iron that at the end of the flame path near the top of the heater, converted the super heated gases to hot air in a plenum above the plates and sent the hot air out to a remote box to be mounted on a wall in an adjacent room with its own air to water heat exchanger in it. This is just the opposite system from what one sees in the local Prompto quick oil change garage. There, an oil or gas boiler in a utility room heats hot water. The water is piped to radiator units near the ceiling equipped with fans. The fans convert the hydronic heat in the finned radiators to hot air heat. This, in combination with overhead gas radiant panels, keeps the garage warm without requiring any “in-the-way” floor border radiation units.
With the cast iron “needled” (or up and down “nail bed”) design, the combustion efficiency could still be kept very high and the danger of steam explosions in the heater eliminated while making the always difficult transfer of heat to remote rooms possible. You can see another photo of this “needled design” in a previous blog article about the panorama door construction series. Sampsa is hiring a heating engineer to assist with the placement and hookup of the external heat exchange system. He already has the radiant floor tubing laid out for his remote bedroom downstairs and his remote bathroom and last week the earth floor in the living area where we built the heater were installed adding almost a foot of height to the level we had worked from. The house designer partner Sven (of Sven and Sarah Johnston) who is also in charge of the plastering and earth floors has now put in most of the earth floors and commented that the heater looks a lot shorter with the floor now pretty much in. Sampsa wrote recently as well and sent a photo of his mom Seija, who lined up all my flight and hotel reservations, sitting on the soapstone bench at the corner of the heater. You can see the new floor height under her feet.
It will be a while before the heater is plastered and the heat exchanger is hooked up. Once the chimney is in place and the heat exchanger is hooked up, it is likely that the heater will be fired a bit to “settle” the unit and have any movement and shrinkage occur before the plaster or stucco is applied. We have sent information on traditional Swedish Kachelugn stuccos to the guys in Clyde. This information was supplied to us by our old friend and colleague in Montreal, Marcus Flynn who alone at Pyromasse, builds some of the most beautiful brick heaters in the world. We will keep everyone informed as the heat exchanger performance unfolds and is documented. The heater efficiency and emissions is all scheduled to be tested once the hook up of the heat exchanger and the chimney is complete. If the system works well, we have made contact with the Finnish firm and are prepared to make it available to clients here in the States. Please give us time to test the system and firm up all the information. We will report on the progress and availability of the system in future blogs.
Near the end of the workshop we had a long discussion with all the members present about how to design homemade effective hot water systems into a masonry heater after they made it quite clear that they wanted to produce clean heat and domestic hot water from one fire, not two. Keep your eyes peeled for news of future developments.
Meanwhile, we will report soon on the amazing securing of a quantity of soapstone for Sampsa’s project and the transformation of this soapstone in just four or five days into fitted polished slabs for shelves, benches, base board and cap trim for his heater. This only happened because of phenomenal co-operation and effort on the part of all the members of the workshop team. While two masons did the yeomans work of laying bricks and another member or two did tending and mixing, every other available hand was involved in securing the soapstone, finding a portable rail saw service, securing a heavy concrete slab, positioning the slabs for the big portable saw and then cutting slab after slab for two days and then processing each slab into the finished pieces. You can see the soapstone trim in place behind Seija, Sampsa’s mom, in the photo above.
Look for the story on how it was all fabricated next.