The cold air often runs out in the summer and the heat doesn't turn on in the winter.

NEVER borrow from a 401K, you are taking pre-taxed dollars and paying it back with after tax dollars, you do not get to return the loan with pre taxed dollars, in addition, some 401K plans do charge interest and maybe even fees, and lastly if you get laid off for some reason, it is a distribution with all the "fun consequences: tax at the last dollar rate, and if you are under 59.5 there is also the additional 10% penalty.Personally I like the HELOC, however you can also sell stocks and do tax harvesting there to offset gains if that is an option

The 2nd group can often be spotted via the credit report, and they are a lot less fun to host (late payments, asking for concessions, demanding, etc.)

Not fun for anyone. 

*As a side note, I think maybe it would be fun also to try and identify where new technology or machine-learning driven approaches could increase efficiency in the spaceAs for my financial situation, personally, I have around 50k saved but 20k of it is tied up in assets I don't want to pay capital gains tax on.

Pic for fun.

OTH is fun to fly into even on United.   

Here’s a fun way to think about getting your spouse on board: focus on what not to do.Don’t talk about REI every single day.Too much can be overwhelming.

Also control the thermostats so the tenants don't jack up the heat in the winter giving you a massive bill.

Heating costs go up in winter, as does electricity due to the reduced natural light and more people indoors.