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A
ir Vent
A device used to purge air from the circuit. It should be
located at the highest point in the circuit.
Auto-Reduce
Reduces 5 degrees with every new call
Reduces 5 degrees every 30 minutes of no demand.
Branch
The section(s) of supply and return piping, including the
heat distribution units connected directly to the trunk.
Also referred to as a “zone”.
Circuit
Entire water circulation piping, beginning and ending at
the boiler (Series Loop System).
Expansion Tank (Compression Tank)
Installed in the circuit to accommodate excess water
produced by heat expansion.
Diaphragm Expansion Tank
Used instead of Expansion Tank (Compression Tank).
Internal bladder separates air and water.
Heat Distribution Units
Transfers heat from the water supplied by the boiler to
the area to be heated through the use of baseboard,
convector, radiator, finned tube. Also known as
“radiation”.
Isolation Valve
Used to isolate the boiler from the circuit. It minimizes
the amount of water drained from the system.
Low Loss Header
Used to allow boiler flow to be independent of system
flow so that Primary/Secondary system piping is
unnecessary and system piping is simplified.
Primary-Secondary Piping
Two or more interconnecting circulating loops,
each with its own pump. Primary =Boiler Circuit;
Secondary=System Circuit.
Reverse-Return Piping
Balanced, equal flow (first in, last out) piping. Utilized
with multiple boilers and/or radiation. Applied with
single or multiple system pumps.
System Purge Valve
A device used to purge air from the circuit. Should be
located as close as possible to the cold-water feed, but
not immediately after the cold-water feed.
Temperature Controllers
The primary temperature controller maintains all
normal heating operations.
Thermal Targeting
Monitors thermostat activity to adjust the boiler
temperature to the minimum output required to meet
heating load.
Thermal Boost
Boosts in 10 degree increments at timed intervals
Up to Hi- Limit setting. Uses target differential of 20
degrees.
Trunk
The section of piping which connects the boiler return
and supply with the branch(es). Also known as a
“main” or “header”. Should be same size as boiler
inlet/outlet connections.
Zone Pump
Circulator installed in branch piping that diverts hot
water coming from the boiler into various areas
(zones) of a building.
Zone Valve
Diverts hot water from the boiler into various areas
(zones) of a building.
11.E Glossary of Terms
M
INI-
T
HERM
JX
Residential Boilers
®
