I love my portable electric oil filled radiators and was inquiring if anyone knew of a domestic version that can be wall-mounted for permanency yet be plugged in to avoid rewiring.

Old Cambridge, Back Bay and Beacon Hill in Boston, Lincoln Square, the Upper East Side, SoHo, Park Ave, West Village etc. in NYC, Haight-Ashbury in San Francisco, Bel Air in LA, Old town Charleston SC, Georgetown DC, Capital Hill, Wash Park, Cheesman, Country Club, Belcaro, Highlands in Denver, the list goes on these are all among both the oldest and most expensive real estate locations in the country.

I haven’t been able to test it out yet, but the previous occupants had a portable fireplace in there.

If it's the windows, all they have to do is wipe them once or twice a day, keep the blinds/curtains open so air can circulate, and ventilate the house at least once a day for 5-10 minutes to reduce excess moisture.Mold is not as bad as people think and is usually easy to deal with.

Maybe you could install vent louvers or  wall registers to allow warm air in the pipe chase. 

How much should it cost me to buy and install 2.5 Ton decent quality air condition system for a SFH?

In general, there are three options on most mobile homes: 1) central gas unit 2) central electric unit and 3) electric window heat/air.

My old boilers tend to last forever (compared to newer forced air furnaces) so I will generally lean towards repairing them when necessary.

Just keeping the air filters changed would have the biggest impact.

An air filter is $4 each... and need to be changed every 3 months.