Befriend the maintenance person if possible :)The only way to 'solve' this if its a boiler/comprehensive system design issue, that I can think of, would be getting creative with some sort of a basic heat exchanger system that essentially takes some of the excess heat and 'transfers it' somewhere other than the water. 

I’m taking several tools from a black light flashlight to moisture meter to thermal camera to check everything out and smell the smell for myself to see if I can figure it out.The vent stack for the water heater is a straight shot vertical up, and is a solid piece going to the roof, same for the furnace.

McGaughe" on the subject.There are state and federal laws to consider.From the SEC website:The federal securities laws define the term accredited investor in Rule 501 of Regulation D as:a bank, insurance company, registered investment company, business development company, or small business investment company;an employee benefit plan, within the meaning of the Employee Retirement Income Security Act, if a bank, insurance company, or registered investment adviser makes the investment decisions, or if the plan has total assets in excess of $5 million;a charitable organization, corporation, or partnership with assets exceeding $5 million;a director, executive officer, or general partner of the company selling the securities;a business in which all the equity owners are accredited investors;a natural person who has individual net worth, or joint net worth with the person’s spouse, that exceeds $1 million at the time of the purchase, excluding the value of the primary residence of such person;a natural person with income exceeding $200,000 in each of the two most recent years or joint income with a spouse exceeding $300,000 for those years and a reasonable expectation of the same income level in the current year; ora trust with assets in excess of $5 million, not formed to acquire the securities offered, whose purchases a sophisticated person makes.The aforementioned is personal opinion and none of the content should be construed a binding offer or agreement.

These expenses include: Contributions up to 6% of the sales priceDecorating allowancesRepair allowancesMoving costsNote—a dollar for dollar sales price reduction is also required for - Excess rent credit and gift funds not meeting FHA requirements Contributions exceeding the actual cost of prepaid expenses, discount points and other financing concessions Credit Requirements Required is 600.

It seems to me that excessive candle use could be seen as negligence and that both the tenants and us would be sued in the case that fire caused by them created losses for others in the building.

If the tenant caused significant damage in excess of $10K, good luck collecting from the tenant even after you win in small claims.There are financial institutions out there that help landlords in your exact situation!

I just put a little sign up in the bathroom that says "Please use the dark wash cloths (located in drawer below) to remove make-up or excessive dirt.Thanks for your cooperation!" 

From experience properties that are typically non owner occupied will carry higher assessments, sometimes even in excess of purchase price. 

Also check in your market to see how your electric company handles solar panels - in many areas any excess electricity your panels generate go to the grid and you get a credit on your bill - which isn't helpful if you owe nothing to begin with.So when do you truly see 'gains' from the installation of the panels and how long do you plan to hold the property?

We are in Colorado (near Denver) and noticed moisture in the basement.