(...taking 60F water, making it 212F degrees, to produce 72F degrees) If you installed 'staple-up' radiant floor tubes under the floors of your units (assuming you have access to them via a basement or crawl space) you would only need to heat your floor tubes to about 80F or 90F to produce that 72F ambient air temperature.

I modelled one of our student rooming houses (1400 ft^2) and every degree over 20C when the ambient outdoor temperature is -10C (warm winter day or night) costs ~$15/month.  

I contacted some mitigation companies today and it looks like $3-4K to have a "ambient" treatment performed where they heat all units to 130+ degrees for 5 hours and then spray with chemicals. 

If you have pipes run in insulated cavities or runs that are mostly beneath ground level, I wouldn't be too worried as the ambient temperature wont drop as drastically as the exterior. 

The vacant unit may be colder than the occupied unit but just the ambient heat from the other unit is enough to keep pipes from freezing, especially when coupled with that running furnace in the basement.

Then there's the actual art of capturing the property using flash, HDR, flambient (flash and ambient blend), and other variations.$1000 could be tight to get a basic camera body, lens, speed light and a tripod depending on what brands and quality gear but it's doable.

Seth Borman oil heaters are perfectly reasonable and produce better, non-drying ambient heat.

My home is an A-frame style with an open upstairs area, so there is a quite a bit of ambient air that needs to be heated before i run into over heating issues.

If the condo has a value of $1,000,000 and appreciates 1.5% (ambient rate of inflation) then your gain would be $15,000 if you held one year and sold. 

@Peter Morganif you can get a 20 degree split from the ambient temp outside, consider the system running as it should.