What matters is the date, and the date exists
Every one of these components carries its own age, physically, on the unit. This is not something you need the seller's memory for.
- The water heater has a rating plate near the top of the tank, usually with the date encoded in the serial number.
- The furnace carries a dated label inside the burner door.
- The air conditioner carries one on the condenser outside.
- The panel carries a label inside the door, and any permitted work on it has a record with the electrical authority.
One photograph of each takes about a minute and replaces the entire conversation.
What each one is worth being wrong about
The reason to bother is that the gap between newer and old is the difference between a component you inherit and a component you buy.
- Roof: $8,000 to $18,000, and asphalt shingle lasts about twenty years for three tab, closer to thirty for architectural.
- Furnace: $3,500 to $8,500, and fifteen to twenty five years is the normal range.
- Water heater: $1,800 to $2,800 for an owned tank, and eight to twelve years is the normal range, which is short enough that newer genuinely matters.
The follow up that gets a real answer
Do not ask whether the roof is newer, because you will get the word back. Ask what year the roof was done, and whether there is paperwork for it.
A seller who replaced a roof five years ago has the invoice and is glad to produce it, because it is worth money to them. A seller who says newer and cannot produce a year has told you what you needed to know without meaning to.