Other than the added cost of the paint/coating - what am I missing in your perspective of "significant investment for a couple more years"? I have been pondering the idea of adding one of these HX's to my homemade boiler that I have been using for 3 years now. They require corrosion resistant materials, such as stainless steel, and also require either forced draught or induced draught to ensure that the flue continues to exhaust properly. You can't get an overall efficiency in a combustion appliance much above 85% without condensing some of the water vapour in the stack gas. The Magic Heat Reclaimer should be installed a minimum of twelve inches (max 24") above the stove or above the nonadjustable elbow from a side or rear vented appliance.

The Typhoon heat exchanger connection diameter 120 mm and 6 pipes with damper sheet steel increases the heat exchange surface and heat output, saves energy costs and protects the environment. I used to only work in there when I knew I had at least 3 hours available, due to the length of time it took to heat, and the cost of kerosene. Have you ever done a heat loss calculation and radiation survey to see if the boiler is properly sized? Obviously dont want to design something that will just build pressure then blow off through its safeties every time the heat storage tank gets full.Maybe another idea is to perforate larger plates, rectangle plates almost the size of the square footage of the fireplace, with a hole saw.

So far I have a relatively successful stove welded up that has preheated primary and secondary combustion air, lined with firebrick, and has forced air combustion (which can thus be controlled by varying fan speed). degree bend straight out of the wall behind it 8inches hole through the wall with Midtherm followed with a y piece incorporating a sootbox and then up onto the roof all in 8inch outer 6 inch i/d stainless pipe 1inch rockwool insulation works a treat! Much less than that, and you'll need to clean your flue multiple times every winter, which can be a huge PITA when it's snowing and blowing.Making a sealed fire box appears to be a better idea - that makes it possible to control the fire with air control and damper.

One was a risk of CO being formed, I'm not sure why that would happen since it wouldn't change the boiler itself, but the boiler is located outside in a separate boiler house, so if any was formed, it wouldn't be a risk to people in the house. It is important to note that even the most efficient heating appliances let a large quantity of the heat escape up the chimney (flue) in the form of hot air, gases, and smoke. Thats easy enough - an electric fan on the chimley cowel would consume, im sure, much less energy than the hot gas holds.consider the extra fluegas resistance you are creating in your design, any reduction in fluegas cfm directly reduces heat output, weather or not what you are creating will capture more heat than the reduction you created with the heat exchanger would be a good documentation. Clean with a long handled, stiff bristled brush using soap and water, cleaning solvent, or a commercial soot remover. All of the gaps that are left between my weld tacks will be taken care of later in the instructable.

The open area (gap between tanks plus 3" tubes) is about 88 square inches, versus the area of a 6" pipe which is about 28 square inches, so this should not obstruct flue gases significantly.

There are numerous technical reasons why the boiler has to have a somewhat elevated stack temperature. If I was going to start on some kind of project like this, I think I would start with a used boiler that had tubes and work on the firebox end of it.