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A controversy has been raging for the past few decades. From my first days of teaching the IBR courses, I have been reminded that few suppliers or contractors really want to put in a small boiler and minimum baseboard. My IBR course was about learning how to install the smallest necessary boiler, baseboard and piping, in order to enjoy a maximum profit while bidding less than others. This conflicts with a more natural desire to put in a larger boiler with wall-to-wall baseboard to give a base for a larger markup. So, the controversy rages on--sometimes within the same person.
The conflict is even worse when these desires oppose doing a heat estimate. In the first instance, doing a heat estimate requires that the person attend to math--not a particularly enjoyable pastime. Secondly, heat estimates are done, for the most part, by suppliers for their customers. Twenty years ago, I made a really fast IBR computer program that many major suppliers used and that I have updated for more accuracy. Some of the boiler companies in these last few years have begun to give away similar programs for free. This is an interesting gift--a device to stimulate more accurate heating installations that sell smaller boilers than the curb or 40-square or 5-cube methods of guesstimation.
A serious conflict resulted from the construction energy standards of 1990. The insulation was increased to the point that heat losses of buildings are a third that of those of 1950 and half that of 1970. The 40-square or 5-cube methods guarantee a heating appliance twice as large as necessary. To make sure, many installers use the curb finger method, so their boiler runs 10 minutes out of the hour in the dead of winter. (If they would only pipe their neighbors to the system so they could do district heating.)
New Developments Cure the Dis-EaseDecades ago, I was told of exciting experimentation with aluminum heat exchangers. Efficiency improvements come with condensing the water produced in a fire. To get over 87% efficiency, water runs to the bottom of the boiler. This is corrosive, acidic water that wears cast iron and steel boilers. An intermediary preventive measure was to let the boiler casting part stay above condensing temperature and use a secondary exchanger of copper in a plastic case. The cure for a ferrous exchanger might have been exotic coatings or stainless steel boilers to match the stainless flues. Today's answer is to use an aluminum casting with extended exchangers. Aluminum blocks and radiators have been in cars since the Corvette was new.
To maintain a competitive price, burners were either on or off; they did not modulate (change input to meet demand). Now that the boiler is made of less material, the burner can be more exotic. European combi boilers have been on the market for decades. It makes no sense to leave American manufacturers out of a possible market. Thus, burners in new models modulate--some down to 20% of the maximum.
This Is Really 'Having Your Cake'It seems that now, as long as your maximum heat loss is less than 200,000 btuh, you can install a boiler that will modulate down to 40,000 btuh. Forty thousand btuh is the heat loss of an ordinary 1,600-square-foot residence today. The same boiler can run up to 160,000 btuh or more, depending on the model, to take care of a 6,000-square-foot home. This is really marvelous. You can get a free jacket with each shipment--one size fits all. Buy a dozen of one model, as it takes care of all contingencies. Add a hot tub, snow melt, whatever. This one boiler does it all.
You don't even have to figure baseboard. As long as you install roughly the right proportion for each room (or use non-electric radiator valves on a one- or two-pipe loop), you can put in more than required without worrying about condensation in the flue or boiler--it is going to condense like it is supposed to. So, the free computer program used to proportion just the baseboard makes sense. I can hear the echoes now: "I just figure the baseboard. The building is less than 3,000 square feet--don't worry about it, it'll do the job. I don't have to lift a finger out at the curb anymore."
Instead of a 180 degrees maximum water temperature, design for a 140 degrees maximum water temperature and use twice the baseboard that you used to in the old days. Also, a low water temperature is just perfect for radiant floors. Insulate an old home that has the original cast iron radiators, and the old radiators are twice as big as necessary to heat the home at 180 degrees F water temperature, but they are just perfect at 130 degrees F (what they usually run at now).