Chimney liner for existing system or side vent for future
I'll set the situation up...
We purchased our home 18 months ago. It came with a 2 year warranty. Our gas water heater has been a bit funky, and the warranty company will replace the thermostat. However, the previous owner installed the water heater 8 years ago without pulling permits, and in the installation process did not install a flue liner system. Now, the service company will not install a new thermostat until the venting system is brought up to code, and those updates are on us.
The reason this is an HVAC question is because we also have a gas boiler that will vent through the same system. It's fairly old, and while we're hoping it fails in the next few months so it's covered under the warranty, it's entirely possible that it will keep chugging along for a few more years.
As we look ahead, we're asking the question of whether it makes more sense to prepare for a new system with venting for the water heater and boiler through a lined chimney or to go with a side vent system? Here's the factors:
-We could get a slight credit now instead of them replacing the thermostat and put in a new water heater. If we do a side-vent water heater, we save the cost of a chimney liner (quoted between $900 and $1100) -- except for the fact that the current boiler still vents through that chimney.
-Knowing very little about HVAC, I don't know the options that exist for boilers, cost comparisons between vertical-vent and side-vent, or mid- to long-term plans for efficiency regulations and how that will affect new installations.
-One service tech also suggested the idea of switching to a forced-air system, which would of course allow for central air. However, not sure about the loss of headroom in the basement - it's unfinished, but we do use it for recreation, and again about the cost comparison between that and sticking with a boiler/baseboard hot water. (We really like the hot water heat but wouldn't mind the AC)
And I'm sure there's other considerations to be made in this process. I'm sure there will be a variety of opinions on this topic, so I'm primarily concerned about mid- to long-term regulations, how those may affect anticipated cost, and making the best financial decisions for both the short-term and long-term (if it's even possible).
If it helps, we're in a 1000 sqft single story rambler in Minnesota. Chimney and mechanical are located 6-9 feet from sides of the house