This is a very common and vague statement used by home inspectors to cover their butts.. All though they do know that the system can be fully functional for another 15 years !
You can ask for it, when they say no, then you can ask for a 1 year homeowners warranty from an outside agency that will cover the equipment for the next year and then if you feel you want to continue the service, you can on your terms.
When it comes to furnace and ac it depends who is the manufacturer, what is the model and what is it made of as well as what is thc fuel service, cast iron boilers can last 50-100 years, so way past any recomended life, stel boilers dont last as long, gas furnaces last loinger than oil furnaces, you can replace th burner and thefurnace itself could last forever if maintained. The same with ac units.
If you are concerned you should get a quailified hvac tech that is experienced in the brand that makes the boiler and ac unit.
good luck with your purchase
It means that they will use a lot more energy than a new unit would. You could find out that replacing them will pay you back in saved energy costs in 5-10 years. That means you are better off to trash them and buy new regardless of if they work great or not.
A number of them have special arrangements in transactions such as yours. For instance, the seller can buy the warranty (which protects the seller until closing), then have it transferred over to you. And sometimes the payment isn't due until closing. Again, your Realtor can fill you in on the details.
Another possibility for some of your systems is to get a service contract from a local company. For instance, you might have a local air conditioning company that, for $500 a year, will make semi-annual inspections and do semi-annual cleanings, will cover most repairs, and will put you at the top of their priority list for service. Lots of HVAC companies offer that sort of program. And the equipment doesn't have to be new, or bought from that service provider.
Hope that helps.
You could also call several HVAC pros and plumbers to get some price quotes, and use that info to help you come up with any amount for the seller concession.
Typically, I'd present both options, and give the seller a choice. Now, it's possible that the seller might also tell you to take a hike, but you'll never know what the seller is willing to do if you don't ask.
Call an hvac (acronym stands for heating, ventilation, and air conditioning) company for a quote on the furnace and ac compressor. They will need to visit the property. A plumber will quote the water heater. Good luck. Hope this answer was helpful.