I have an older Le Creuset lasagna pan. For some reason, I put it in the oven to get it off the counter and forgot about it. I turned on the broiler one night and after a while I smelled a strange odor. I opened the oven and saw a smoking brown pan and realized it was my red/orange lasgana pan! The enamel was melting, or so it appeared. I immediately and carefully took it out and placed it on some trivets. The orange enamel was now completely chocolate brown colored. As it cooled, the orange color started to come back. It seems to be OK, but I definitely think you can harm the enamel if it gets too hot.

"Cast iron steam radiators under windows are rare in all but the smallest of rooms..." What? I grew up in a town where many of the houses were heated with steam, including my house. IIRC 17 steam radiators, added well AFTER the house was built, and every one of them was located under the windows. The same was the case in the homes of my friends. The house my Mother lives in right now was originally built with gravity hot air, but around 1912 was converted to gravity hot water. All of the radiators are located under the windows. Steam radiators don't solely rely on height to delivery heat. Just as with hot water radiators, steam radiators can be made shorter and longer to increase the radiation surface. The radiator under the bank of windows in the dining room was 24 sections, height was about 30 inches. I'll stick by my original assessment -- unless the owner is willing to put a rather massive amount of money into an old home -- totally new systems, insulation, windows -- a simple switch from steam to forced air doesn't make much sense. That may, or may well not, be appropriate, feasible, and possible. I'm certain, though, that if you do have 40 years of experience in this that you'd know there's often a point of no return where spending money to make upgrades is not only a waste of money, it's foolish.

If you have natural gas available that's the most economical with propane coming in second unless you cut your own wood. But economy is moot when heating a screened porch. That makes resistant electric or heat pump the best choices for peace of mind if worried about safety.

"In this engineering study of 1996 I can't find what the R value is of the duct work in the attic." If it's not stated, I'd argue that it doesn't matter anyway. The study compares the performance of one home with a vented attic and two with unvented attics. As long as the R-values of duct insulation were the same in the three homes it's not a variable. "Two days were chosen of the Las Vegas house when the outside air temperature was 92 degrees. Why only two days and why not a hotter temperature for mutlipe days?" Read the report. Construction activities surrounding the site affected the data collection and some of the days were atypically cool. The two days were deemed adequate by the researchers to compare the homes in the same development with vented vs. unvented attics. "Do we assume the losses would be the same for the coldest and hottest climates? " The purpose of this study is stated in the abstract: "It has been suggested that by moving the ceiling air barrier and thermal barrier to the plane of the roof, that better building airtightness can be more easily achieved, and that the elimination of heat gain to the attic air distribution ducts would more than offset the additional heat gain caused by not venting the attic (emphasis added.) To investigate this further, both a computer modeling study and an experimental study in Las Vegas, Nevada were carried out." Except for homes with flat roofs, the heat transfer areas would be different so you couldn't translate the results. That said, the finding that air leakage was the most significant contributor to differential energy usage would, in my opinion, apply to both heating mode and air conditioning mode. There are other ways to reduce with air leakage which may be a more economical alternative and which would eliminate some of the potential drawbacks with unvented (conditioned) attics.