I have a gas tankless water heater ready to mount on an external wall. It is in a finished basement with no immediate access to a floor drain and the climate is too cold for an external drain. The hot water outlet pipe travels to the old water heater location before teeing into the existing plumbing. Can I install the pressure relief valve at this location, approximately 20 ft away, if there are no shutoff valves between the tankless heater and the pressure relief valve? I then could provide a drain line from the pressure relief valve into a floor drain.