Plumbing – Is this a drain-pipe

I have a setup similar to yours and the radon installers put a foam sheet over a hole in my sump cover, almost like a thin sheet of packing foam. This is almost airtight but allows some suction for the fan. You could terminate the drain line over a small hole that was covered with foam or paper such that the the air would be sealed in, but in the case you get water from the heater it would drip through it. You could also put a check valve in the pvc line from the heater but it would have to be loose so a trickle of water would trigger it. A trap would dry out, although the HVAC trap probably dries out during the winter anyway....but the suction from the fan should override that small opening.

The configuration you pictured is not really a good idea. Waste water from the washer is going to flood the heater drain pipe, leaving nasty residues that could conceivably siphon back into the heater if connected to the heater drain valve. Not likely, but possible any time two drains are connected at different levels other than directly into the vented out flow pipe. The other problem will be that if the drain is a open pan drain only, washer waste water will back up into the pan. Washers tend to eject water quickly and can partially fill the pipe above the trap.

I would rather see you pump it up to the inlet of the washer drain.