It is possible that a car can smell like gas when the heater is turned on for a few reasons. One possible reason that this happens could be a leak in the line.
You have a leaking heater core. You might smell antifreeze if you turn on the defroster.
Possible mouse nest in the heater box or duct work in the car.
Leaking heater core
You might have a gas leak in your front engine compartment. The heater pull in air from the front and therefore if you got a gas leak it will pull the smell in get it check asap.
There must be a gas leak. Contact your gas supplier IMMEDIATELY, if the smell is in a house. If it is in a car, have your mechanic check for a leak.
If you try turn on the heat and a huge cloud of smoke fills your car, or you can smell burning anti-freeze....then you have a busted heater core.
It probably has a leak, possibly from the heater core.
There are several things that could be going on. The most common thing that would make your car smell like gas when the heater is on would be a bad heater core.
i believe your heater core has died
Likely as not there is a coolant leak, perhaps in the heater core.
A car heater that smells like burning rubber could be an indication of a belt that is slipping. The slipping belt smell can be drawn in from the engine compartment into the passenger cabin.
it should NOT.......you have a GAS leak fix it ...unless you overfill gas tank then maybe that's smell temp.