Size of radiant and control systems

Wayco Wayne

to issues that came up when I asked about sizing an injection circ on another post. It was suggested by 2 Wallies, whose opinion I have the highest regard for,(Hot Rod, and Heatboy) that an injection system might not be the control method they would recommend for a smaller radiant floor system. What kind of system would be recommended and where do you draw the line. How do you take into account boiler protection, if there are other heating systems on the boiler? Is outdoor reset and constant circulation not necessary under a certain size capacity?? My local W/M rep once told me that up to a certain percentage Cast iron boilers could withdstand a certain amount of cool return. Is this also true? Thanks for your input on these questions. It's raining again in MD and like DH I have to much time on my hands.

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Mike T., Swampeast MO

As Dan suggests in \"Pumping Away\"

a simple two-way valve is often a very good choice to add a small radiant zone to an existing system. They're reliable, inexpensive and straight-forward in operation.

Atmospheric cast iron does seem to deal with low return temps--even very low--BUT I have only dealt with systems of high mass, high volume and oversized boilers. Such ability seems to come at the price of efficiency however.

Personally, I think buffering is about the best way to use a non-condensing boiler on systems of high mass/volume. It allows you to keep boiler efficiency up by producing water much hotter than required, yet keeps quite long cycles by virtue of a large differential in the buffer tank. Problems with "micro-zoning" essentially disappear as the buffer provides reverse feedback. Of course it comes at a cost--not only for the equipment but the heat loss of the tank itself. Unfortunately, it comes back to "condense or not to condense?" which in turn leads to "will condensing equipment last?"