QHT BIASI 3 WOOD, Instructions Manual

29 

C. 3WOOD 

Boiler

with circulator 

Piped in Parallel with Oil/Gas Boiler      

In the traditional American baseboard, hydronic system, the heating temperature in the house or zone is controlled by circulating 
or not circulating water of a fairly high and relatively constant temperature to radiation.  The thermostat used in such a system is a 
simple switch to a relay which turns the circulator on and off.  The vast majority of American heating systems use cast iron 
boilers which have internal tankless coils for producing domestic hot water.  The parallel piping arrangement is the correct 
application for maintaining temperature in the oil/gas boiler with wood heated hot water as well as heating the radiation in the 
house.  Since the specifics of such a system will vary from installation to installation, the following procedure provides an 
example of one specific installation which can be used as a model for actual situations. 

1.  Insure that the existing system has flow checks or electric zone valves in the supply lines to the various heating zones, and that the 

Space heat and DHW circulators are mounted on the return line going back to the Oil/Gas boiler.  If not, they must be installed in 
these locations. 

2.  Remove the existing radiation supply and return lines from the oil or gas-fired boiler.  Install pipe tees  on the supply and  returns 

from nipples coming out of the existing oil/gas boiler.  

NOTE

:  Occasionally, extra supply and return taps are available on oil/gas 

boilers.  These plugs may be removed and used to run the lines between boilers.  Re-install the supply and return lines. 

3.  Install a tee with a 1”branch coming out of the supply tapping of the 

3WOOD 

boiler

 for the dump zone. 

4.  Then install another tee with a ¾” branch for the Aquastat for the 

3WOOD 

boiler’s

 circulator.  Install the Honeywell L4006B 

into the branch of the tee using the 3/4 “ immersion well.  

Caution:  Be careful to maintain a 12” minimum clearance between the 

flue pipe and the 

3WOOD 

boiler aquastat.

5.  Pipe from this tee down to the return tee or tapping on the existing oil/gas boiler. 

Note:  By adding the gallonage from the addition of the 

3WOOD 

boiler,

 an expansion tank should be added or the existing 

tank should be increased in capacity. 

6.  Install a tee with a 1” branch coming out of the return tapping of the 

3WOOD 

boiler for the dump zone.

7.  Install piping, flow check and circulator from 

3WOOD 

boiler

 to the supply tee installed on the oil/gas boiler. 

 
Note:  Aquastat settings for the existing oil/gas boiler should be as follows: 
 

High Limit – 165F 

Low Limit -  150F 

Circulator -  140F 

But these settings can be raised if the 

3WOOD 

boiler isn’t fired for extended

 periods of time.