Quote from @John Carbone: Quote from @Chris Look: Hey everyone, we are looking for some clarification or advice on maximizing the tax benefits on a short term rental.

What @John Carbone said.

If the heat exchanger forms a crack, you run the risk of Carbon Monoxide (CO) poisoning (created from the gas exhaust fumes) escaping from inside the box to the outside of the box which will now entered the house instead of going out the exhaust vent system. 

Over that course of time, both odor and total organic carbon (TOC) levels dropped for all of the pipes.

Got in the house today and the biggest problem is a basement wall crack which looks like a serious problem.Have not done a house with this type of problems so not sure how much $$$ we are taking about.My plan is to use carbon fiber cloths with epoxy.Option 2 is to use anchorsThis retaining basement wall is about 480 sq ft (60ft long by 8ft tall).

Quote from @John Carbone: Quote from @Michael Baum: Hey @Dolev Zaharony, great answers here for you.

Quote from @John Carbone: 1 beds and 4 beds are optimal. 2 and 3 beds are traps How so?

I'd be good with cash but I'd give them a receipt for each payment and keep the carbon copy.  

Please get a carbon monoxide detector though.

If it was done anytime recently, then you know that the wall is continuing to move since the skim coating wouldn't have cracked if the wall wasn't moving.There are several different ways to repair a foundation without having to replace it such as steel beams, wall anchor plates, or carbon fiber straps with epoxy.