. ($500K multiplied by 80 is $40 million in real estate over the life of the development).

Example:Heat is measured in BTU'sElectric baseboard or space heaters      $35.13 / per 1,000,000 BTU'sNatural Gas                                             $10.02 / per 1,000,000 BTU'sIt is 3.5 times as much multiplied by every month you are paying to heat the property.Here is a free calculator offered on the Department of Energy's website:http://www.eia.gov/tools/faqs/heatcalc.xlsI just wanted to make you aware of your options and any necessary information before taking on that monthly expense.Also, with a central system, you control it (WiFi Stat).

If you pay $495,000 then you are buying at a 7.8 gross rent multiplier.  

Of course run the rest of the numbers. 70% rule ties loosely to the Gross Rent Multiplier and Cap Rate.You say your multiplier is 100. 

***Seeother notes.Down Payment: $0.00Loan Amount: $80,000.00Loan Points: $0.00Loan Fees:Amortized Over: 20 yearsLoan Interest Rate: 5.000%Monthly P&I: $527.96Income1 Unit $1,400.00    2 Unit $950.00Other $0.00Total $2,350.00ExpensesVacancy $70.50 Repairs $47.00CapEx $117.50 Electricity $200.00Water $25.00 Sewage $25.00Garbage $51.00 Insurance $82.00P&I $527.96 Property Taxes $152.92Misc: Fuel oil $275.00Total $1,573.88Buy & Hold Analysis - 08/27/15 04:43:50Financial ProjectionsTotal Initial Equity: $30,600.00Gross Rent Multiplier: 2.84Income-Expense Ratio (2% Rule): 2.87%Typical Cap Rate: 5.00% Debt Coverage Ratio: 2.47%ARV based on Cap Rate: $312,980.0050% Rule Cash Flow EstimatesTotal Monthly Income: $2,350.00x50% for Expenses: $1,175.00Monthly Payment/Interest Payment: $527.96Total Monthly Cash flow using 50% Rule: $647.04House Size (sq. ft) 1500Year Built 1941Year Renovated 2001Units 2Stories 2Property Type Small Multifamily (2-4 Units)County Appraised Value 110600Pool YesHeating YesGarage 1Construction WoodRoofing ShingleFlooring Types Hardwood & CarpetWiring Condition GoodPlumbing Condition GoodSiding Material WoodOther Info: Owner/ buyer will occupy 1 floor unit for 24 months.

Additionally, that same equity could be used to purchase rental properties which would have a much better Gross Rent Multiplier than what you currently have.

You take your NOI and multiply it buy the cap rate to great a fair purchase price based on income.The property has a NOI of $10k/yr      Times      Cape rate of 10    = $100,000 purchase price

I think it is far more complicated than simply one number (Rent multiplier, cap rate irr, etc).  

In most cases appraisals for 2-4 units will rely on gross rent multiplier not cap rate.

There are many issues with this line of thinking:Basically, this is a variation of what is known as GRM analysis (Gross Rent Multiplier).