The units share a wall, heat/ac source, and address. 

If the house is 100 years old with wood heat and split shaker shingles, you need higher capital reserves. 

Also, tell your tenant they can pay for the clean up from that know it all dad who pulled the heat register up and disturbed the flooring if it's required. 

Also did it for a fridge: $220 and it lasted another 5 years before the heating element in the freezer door went out (I had warranty at that point).  

What temporary heat source should I use while rehabbing an apt building in the winter?  

Built in 1973, in great condition, although does not have current upgrades.Since I am not yet a PRO user, I based on my rental calculations using great calculators from ListenMoneyMatters.com.SUMMARY:ESTIMATED VALUE (Zillow): $214,714.00 (In line with averaged real estate agent's Comps but slightly more conservative, as I think he threw in a couple outlier properties to bump the average a bit to entice my folks.)PURCHASE PRICE: $195,000.00 (price based solely on the amount left on my parents 4.25% HARP non-assumable mortgage)UPFRONT COST: $50,587.42 RENT ESTIMATE: $1750.00 ANNUAL NOI: $11,633.00GROSS YIELD: 10.79%CAP RATE: 5.98%CASH ON CASH: 5.56%CASH FLOW:ANNUAL: $2760.32MONTHLY: $230.031ST YEAR EQUITY: $2363.49ACQUISITION COSTS:DOWN PAYMENT: $48,641.75 (25% ) CLOSING COSTS: $1,945.67 (1%) *anticipate only using real estate attorney (no real estate agents) for more cost effective deal and save parents 6% commission; do not know actual attorney fee costs for closing so this number is a WAG (Wild *** Guess).MORTGAGE RATE: 4.5% *anticipated MORTGAGE TERM: 30 years ONGOING COSTS:PROPERTY TAX: $1,927.00/yrPROPERTY INSURANCE: $300.00/yr PROPERTY MANAGER: $175.00/mo (10%) VACANCY RATE: $350.00/mo (20% vacancy rate)MAJOR/MINOR CAPEX: $175.00/mo (10%)HEAT/AC: $92.00/mo (Averaged)HOA: $420.00/mo (has remained approx. $420.00 for decades; although the HOA just hired a property manager for the first time last year, but so far no indications of changing HOA fees)Notes:Rent estimate: $1,750.00 (local property manager assessed realistic rents between $1600-$2000+ per month on long-term lease or as vacation rental $140-200 a night/minimum 1 week stays).My parents are open to any type of creative financing deal, that would free them from paying mortgage (their current monthly mortgage payment is $1,000.00 (+ $420 HOA).

Unit SF Bedrooms/Baths Monthly Rent Annual Rent Retail 750 $ 1,900 $ 22,800 Lease expires in 4 years 1 - Duplex 750 Duplex $ 2,600 $ 31,200 Gut renovated with private backyard 2F 750 3BR/2Bath $ 3,200 $ 38,400 * 2R 750 3BR/2Bath $ 3,200 $ 38,400 * 3F 750 3BR/2Bath $ 3,200 $ 38,400 * 3R 750 3BR/2Bath $ 3,200 $ 38,400 * Total 4,500 $ 17,300 $ 207,600 *Vacant - rent project after renovation REVENUE: Gross Monthly Income $ 17,300 Gross Annual Income $ 207,600 EXPENSES: Real Estate Taxes $ 8,394 Gas/ Heat tenants Electric $ 1,679 Insurance $ 3,375 Water/Sewer $ 2,700 Maintenance 3% $ 6,228 Management/Vacancy 3% $ 6,228 Total: $ 28,604 Gross Annual Income: $ 207,600 Less Expenses: $ 28,604 Net Operating Income: $ 178,996   Any and all input is greatly appreciated, Thank you in advance.   

I would think the target buyer would be much more in the investor camp.So if it was me doing the comps, I would try to find 3-family properties and see if I could establish a rough value from them, and then discount by, say, 10-15% for the fact that 2 buildings on one lot is unusual and there's arguably twice the maintenance (two roofs, two heating systems, etc.). 

We had 3 heat systems and 2 water heaters replaced in 12 months with only 6 units.  

Here is an example from our rental agreement that outlines some of how we do this:MAINTENANCE OF PREMISES.Landlord will maintain all electrical, plumbing, heating, and other facilities and appliances supplied by Landlord in good working order.Landlord will perform periodic inspections of the premises, no less than once a year, for the purpose of property maintenance and repair.Landlord will notify Tenant in advance of the inspection.