Don't install heat trap nipples if house has pressure issues, or pipes get clogged with hard water.
Heat traps will clog, and whistle, hum, buzz, and reduce household pressure.
Make your own heat traps by configuring pipes differently.http://waterheatertimer.org/9-ways-to-save-with-water-heater.html#heat-traphttp://waterheatertimer.org/Low-hot-water-pressure.html#trap
Buy regular di-electric nipples at local box store plumbing department instead of heat trap nipples.http://waterheatertimer.org/images/IMG_1879-di-electric-nipple-300.jpg
If you go ahead and install the heat-trap nipples, look inside the nipple.
Look past the plastic bar that divides down middle.
Notice that one end has insert inside the pipe. While other end does not have insert.
End with insert goes into water heater first.
Notice also if you blow into the heat trap nipple that air flow is constricted.
If air flow is constricted, then water will also be constricted.
This is why heat trap nipples are not recommended.
Why do they have heat trap nipples??
So manufacturers can report higher EF energy efficiency rating for product.
Do heat traps save money. Yes, but make your own by reconfiguring pipes. Save $9.20 per year electric heater, $4.00 per year gas heater.
You can save more money by maintaining water heater, which pays about 10$ per month in future replacement costs.
Or fix leaks, and install dual-handle faucets so lifting single handle faucet in middle does not continually run cold water into tank. This saves $2-$8 per month.