@Kenneth Garrett according to the PA code, if there is a window within 10 feet of a fire escape, that is changed i.e. removing the frame then it needs to be replaced with a fire rated window assembly.

If the property is constantly losing money and it's not a one-off sort of problem (i.e. big turnover or roof replacement, etc.) and you can pull out some money selling, I would recommend selling.

. @ 4% (30% of rent)Even if you want to cash flow just $150 a door, that would be 20% of rent, leaving 40% of rent for everything else (100%-10%-30%-20%=40%)40% of $800 or $320, is then what needs to be left at a minimum for monthly 1) property tax, 2) insurance, 3) vacancy, 4) maintenance, 5) capex, 6) tenant replacement, 7) tenant renewal and 8) lawn maintenance costs. $320 for all these categories just doesn't seem feasible on a monthly basis.Therefore, I think it's safe to say that it's either your cash flow that declines (e.g., <$100/mo.) or you hope there's months with little to no 3) vacancy, 4) maintenance, 5) capex, 6) tenant replacement, and 7) tenant renewal costs, which would be foolish.

. @ 4% (30% of rent)Even if you want to cash flow just $150 a door, that would be 20% of rent, leaving 40% of rent for everything else (100%-10%-30%-20%=40%)40% of $800 or $320, is then what needs to be left at a minimum for monthly 1) property tax, 2) insurance, 3) vacancy, 4) maintenance, 5) capex, 6) tenant replacement, 7) tenant renewal and 8) lawn maintenance costs. $320 for all these categories just doesn't seem feasible on a monthly basis.Therefore, I think it's safe to say that it's either your cash flow that declines (e.g., <$100/mo.) or you hope there's months with little to no 3) vacancy, 4) maintenance, 5) capex, 6) tenant replacement, and 7) tenant renewal costs, which would be foolish.

I would think it is a pretty common size, as the big box stores sell replacement windows in those sizes.

If people living in them have took care of them and/or items have been replaced and routine maintenance done, it may be worth it to keep them.

I replaced this out of my pocket. 

What I did:Painted walls and ceilings with sherwin williams superpaint dover white.Trim and kitchen wainscoting was painted with super paint semi gloss white.Ripped out plaster tub surround and replaced with cement board that was waterproofed and tiled.Replaced some missing shingles on garage roof.Replaced old shower valve with single handle valve.Replaced garbage disposal.Replaced old outlets/switches with new white outlets/switches/plate covers.Jacked up sagging portion of house and sistered three of the joists and replaced the rotted sill plate.Removed vinyl tile from laundry floor and painted the concrete with grey floor paint.Before photos:  Apologies if they are sideways or upside down...The after photos can be seen on my zillow ad, https://www.zillow.com/homes/17439-cicotte_rb/88664724_zpid/?

I guess I'm just considering all the hidden things that would need to be fixed or replaced that I can’t see.

It's an even more toxic charge than a security deposit, replacing "don't expect this money back" with "there is contractially  no chance you will see this money again."