Sunday, October 25, 2015

Residential Combustion Analyzers


To measure combustion efficiency you need a tool that can measure either the oxygen or CO2 content of the combustion gasses. For many years, an hour glass shaped bubbler containing a fluid that absorbs CO2 or O2 was used. They are difficult to find these days. They have been replaced by electronic instruments. These use an electro-chemical reaction in an oxygen sensor to measure the O2 content in the flue gases. They use thermistors to read the flue gas temperature and ambient temperature, so they have all the information that need to calculate and display combustion efficiency. They use this information to display CO2 %, O2 %, combustion efficiency, % excess air, flue gas temperature, and net stack temperature. Most offer other measurements as well. Some of the more common additional features include:

  • CO ppm – to read the CO in the flue gas
  • CO ppm air free – to calculate the CO ppm after removing the excess air
  • Draft pressure – to insure you actually have a draft
  • Differential draft pressure – to insure the draft pressure is lower than the room pressure
  • NOX – to comply with NOX regulations in areas that restrict furnace NOX emissions
  • Printer – to print out reports from results
  • Computer Connectivity – to import data from analyzer to programs on your computer

Prices vary a good bit. From just over $500 for no-frills analyzers intended for residential work, to several thousand for commercial instruments. Certificates of NIST traceability often cost more.  Most combustion analyzers use electro-chemical sensors. These have a limited life because the chemicals in them are used up as they work. Typical replacement time is every one to two years. Some are user replaceable, and others require sending in the tool for the sensors to be replaced. This will typically cost $200 - $300. The table below compares several of the lower priced models which are aimed at the residential market.


Bacharach Intech
Testo 310
UEI C75
E Instruments BTU 900
O2
yes
yes
yes
yes
CO2
yes
yes
yes
yes
Efficiency
yes
yes
yes
yes
Excess Air
yes
yes
yes
yes
CO
yes
yes
yes
yes
Air Free CO
yes
yes
no
yes
Draft pressure
no
yes
no
yes
Differential Pressure
no
no
no
yes
NOX
no
no
no
Can upgrade
Printer
Available Extra Cost
Available Extra Cost
Available
Extra Cost
Available
Extra Cost
Computer Connectivity
no
no
No
USB & Bluetooth
Field replaceable sensor
yes
no
no
yes
Fuels
6
5
5
10
Warranty
2 years
2 years
 3 years
2 year
Approximate Street Price
$520
$600
$500
$1000


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