Most cast iron radiator systems run about 130-140 degrees because it works well with the mass of a cast iron radiator. However, in-floor hydronic is in contact with your feet, so it usually does not exceed about 90- 100 degrees. There are mixing valve solutions available, but they are not very cost effective for only one or two rooms. I came to that conclusion when I renovated my side porch, and ended up using Myson radiators that are much more compact than the old cast iron.

My new addition has foam insulation (including the crawlspace and attic), Tyvek, and all the other upgraded insulation and sealing that makes it much tighter than the rest of the house. Last winter we didn't connect the new radiators until about January, and those rooms were almost the same temperature as the main house. You could probably use much smaller radiators and make them less intrusive if you are doing other improvements as part of your renovation.

Bruce

Have you figured out why this big radiator is not getting hot? Is it the radiator or the supply? You also should look into installing new baseboard or wall radiators. They more attractive and smaller than a 1920's radiator. It would be more compatible with your current hydronic system and a lot less money.

The radiator gets plenty hot. The problem is the lack of insulation. We plan to fix that, and we're looking for another heating solution. I have another room (master bedroom) with an undersized rad - maybe we'll just look a switching them out.

Hardwood manufacturer will be God. We'll put in 3/4 unfinished oak strip and finish it ourselves with Waterlox.