April 14, 2014

The Role of the Low Loss Header and Venting

Combi boilers can provide homeowners with an all-in-one, energy-efficient, whole-home heating and water-heating solution. And, although this type of product has been around for a number of years, not everyone is familiar with some of the more technical elements of combi boilers, such as the low loss header (LLH) and proper venting.


The LLH, also referred to as a hydraulic separator, replaces traditional primary secondary piping, which can simplify installation down to a matter of minutes.

Rinnai’s LLH come standard with ball valves to isolate the boiler. By isolating the boiler, maintenance becomes significantly easier, specifically when servicing major components, as this allows contractors to quickly turn the water flow off to and from the boiler.

The LLH, which helps to balance the flow between the system loop and boiler loop, also:

  • Allows quick isolation of boiler from the heating system for service and maintenance;
  • Simplifies and speeds up installation;
  • Saves labor and materials on site during installation; and
  • Has a compact design, which saves space compared to closely spaced tees.


The second possible need when it comes to installing a high-efficiency combi boiler may be new venting—especially when replacing a traditional non-condensing boiler. There are several ways to vent the boiler and among the safest is concentric venting—essentially a pipe within a pipe. In concentric venting, fresh air is pulled in through the outer portion of the two-pipe vent and the center pipe releases exhaust.  A second venting option is a two-pipe installation—one for intake and a separate pipe for exhaust.

Each option has benefits and should be considered on a case-by-case basis when installing a high-efficiency boiler.