underestimating costs and paying to heat vacant homes in the winter....

Whether you are trying to keep the heat in (most of the year up here) or out (most of the year in Florida), the better the thermal break of the envelope, the lower your energy costs.

Perhaps the jury is still out on the long-term effects of climate change/global warming but I don't like what I see and states in the Southwest including California do appear to be at great risk in the long-term if the climate continues to heat up.

The home only has window units and the seller does not have the funds to install central heat and air which is the main thing holding this house back.

Thanks to that show we had insulated our personal residence such way that our average Heat/AC bill is now $120 month for 2400SF!

If so your QI has the proceeds from your sale and you're in the 45 day identification period and feeling the heat of trying find the right replacement property.  

I figure it would cost me $15,000 to $18,000 to rehab including new vinyl siding, heat/ac, and creating a sun room from the current large covered and screened deck/patio.  

The thing is you can go on and on and on about these rules...Do not strike a match near the gas stove and oven.Do not jump up and down on a bed while the ceiling fan is running.Do not park in your neighbor's designated space.Do transfer or retrieve your clothes from the washer and dryer promptly.Do lock your doors when you leave.Do not leave a burning BBQ grill unattended.Do clean the lint screen on the dryer after use.Do not puke directly into the community waste bin when drunk.When your neighbor's dog drop heat on your door step, please resolve the issue with the neighbor, do not smear such dog poop over his/her door knobs.......This list can be endless though. 

From researching this topic, one thing I know I'll need to check is the lowest incoming water temperature, so I'll probably wait until February to try to capture the lowest incoming water temp, so I can choose the correct size tankless water heat.  

Due to a heat duct that runs floor to ceiling in the wall, I plan on extending the doorway opening from three feet to six feet and leaving the duct work in place to save time and money.