A union is needed so a unit heater can be disconnected for service. Where is that union permitted to be installed?
- AInside the wall chase, so that the finished space stays clear of fittings
A wall chase is a concealed location. Unions and similar mechanically sealed fittings are prohibited there because a slow leak would go undetected.
- BAbove the suspended ceiling where the branch tees off the main
Space above a suspended ceiling is treated as concealed for this rule, so a union is not permitted at that tee.
- CUnder the floor in the crawl space where the riser turns up
A crawl space under the floor is a concealed location for fitting purposes, and a union there could weep gas into an enclosed area beneath the building.
- In the exposed piping at the appliance, downstream of the appliance shutoff valve
Why D is correct
The union is placed where it is exposed and where it is downstream of the shutoff valve. That location lets a technician close the valve, break the union and pull the appliance without disturbing the rest of the system, and it keeps the mechanically sealed joint in view for leak testing at every service call.
What this question is testing
This tests whether you recognize which locations count as concealed and whether you can apply the concealed-fitting prohibition to a real routing decision.
On the job
The practical version of this rule is that everything mechanical happens in the last few feet at the appliance and everything concealed is welded or threaded and fully made up. On a unit heater hung from a ceiling, the union goes after the drop, after the valve, with the sediment trap in the same short assembly. Inspectors look for bushings too, which get used to step a fitting down and are prohibited in the same concealed locations for the same reason.
Memory technique
If you cannot soap it later, do not screw a union there.
Exam tip
Ask whether you could put a soap solution on the joint after the building is finished. If not, the fitting is in a concealed location.
Where to look it up
Piping system installation, including fittings in concealed locations, is IFGC Chapter 4, Section 404. UPC states cover the same ground in UPC Chapter 12 or NFPA 54.