Boiler bypass

Bypass Differences

As Ed stated, a System Bypass mixes some supply water with the return water to aid in keeping the boiler return water warmer. The primary concern though is reducing the possibility of flue gas condensation and not neccessarily thermal shock. In a System Bypass the system circulator(s) will always need to be on the boiler side of the bypass connection.

The Boiler Bypass differs in that it diverts some of the return water to the system supply in an effort to simply reduce the amount of cool return water that flows through the boiler. This reduction of return water flow will allow the boiler to remain at an average water temperature above the dew point to keep flue gas condensation from occuring. The secondary feature is that it causes a mixing action where the diverted return water mixes with the boiler supply water. Location of the circulator(s) on the Boiler Bypass will always be on the system side of the bypass connection.

While both types offer some degree of protection, neither are a guarantee against either flue gas condensation nor thermal shock. Other types of piping configurations such as primary-secondary and variable speed injection prove to be more effective but still are not bulletproof! Only systems where actual return water temperature is monitored and some sort of modulation of flow from the supply to the return are close to being protection you can count on. This type of configuration is already built into the Burnham Revolution gas boiler. It is safe with return water as low as 55°F without flue gas condensation concerns.

Glenn Stanton

Manager of Training

Burnham Hydronics

U.S. Boiler Co., Inc.