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Williamson-Thermoflo FS-80 COMBI
Williamson-Thermoflo FS-80 COMBI
Williamson-Thermoflo FS-80 COMBI
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Williamson-Thermoflo FS-80 COMBI
Williamson-Thermoflo FS-80 COMBI

Williamson-Thermoflo FS-80 - 73K BTU - 92.4% AFUE - Combi Gas Boiler - Direct Vent



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Was $2,339.00
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Williamson-Thermoflo FS-80 - 73K BTU - 92.4% AFUE - Combi Gas Boiler - Direct Vent
Williamson-Thermoflo FS-80 - 73K BTU - 92.4% AFUE - Combi Gas Boiler - Direct Vent
Model: FS-80 COMBI
Was $2,339.00
Product Q&A
How-To Articles

Recommended Accessories

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Expert Recommended Accessories Selected by Bob, our Expert
Required Accessories 9
These accessories are required to properly setup/install this product.
Optional Accessories 10


    Keep your home warm and heating costs low with the Williamson-Thermoflo Freestyle combi-boiler. The Freestyle FS-80 COMBI boasts an impressive 92.2% AFUE efficiency rating, making it one of the most efficient boilers on the residential market. Easy to install and even simpler to maintain, the Freestyle boiler comes with a wall mount allowing it to fit into almost any space with its compact design. A crystal clear digital display allows for easy access to important information as well as the ability to quickly and easily adjust any of the boilers settings. The FS-80 COMBI comes standard with multiple features designed to keep energy costs down, including its modulating combustion system, allowing the FS-80 COMBI to run reliably while saving you money. As a Combi model, this boiler comes with a built in domestic hot water heater and circulator pump, allowing it to provide endless hot water to your showers, sinks, and home appliances. The Freestyle series runs standard on natural gas, but can be converted to propane with a simple adapter, making it flexible enough to be used in any home.
  • Higher Efficiency, Lower Costs
  • With an AFUE efficiency rating above 92%, the Freestyle boiler is one of the most efficient on the market. With its ASME rated heat exchanger and modulating burner, it will not only lower energy costs, but help reduce your carbon footprint as well.
  • Factory Tested
  • All Freestyle boilers come factory tested and certified by top industry analysts ensuring they will remain reliable and efficient for years to come.
  • Unmatched Flexibility
  • Each Freestyle comes with its own wall mounting kit. Combined with the boiler's compact design and multiple venting options, the Freestyle boiler can fit into nearly any residential space.
  • Built in Hot Water Heater
  • The Freestyle Combi models come with a built in tankless water heater. Using its built-in flat plate heat exchanger, the Freestyle Combi unit can provide hot water for your entire home.
  • Product Includes
  • (1) FS-80 COMBI Freestyle Boiler
  • (1) 640-000-044WT Wall-Mount Kit
  • (1) 640-000-037WT Condensate Trap Kit
  • (1) 640-000-017WT FX3-FP Circulator


specs product image PID-58496
Product Category
General Information
Product Line
Product Category
Medium Learn More
Medium refers to the substance that carries heat through the heating system. Systems are either designed to use either Hot Water or Steam as a medium, and components are usually specific to one or the other.
Hot Water
Fuel Type Learn More
Fuel Type
To create heat, some form of fuel is required. Fuel Type specifies what the product uses as an input to create heat.
Natural Gas
Combustion Type Learn More
Combustion Type
Condensing appliances use leftover thermal energy from combustion gases to heat water in a secondary heat exchanger, resulting in higher efficiency and lower exhaust temperature.
Vent Type Learn More
Vent Type
Products that use combustion (burning) of fuel to create heat also create potentially dangerous gasses that need to be exhausted (AKA "Vented"). Depending on the product, venting can be done via a chimney, through a side wall, or use a second vent to provide fresh air to the appliance.
Direct Vent
DHW Production Learn More
DHW Production
DHW (Domestic Hot Water) is potable water for uses other than space heat. Some boilers are able to provide DHW "out of the box", while others can do so with the purchase of optional accessories.
Modulating/Staging Learn More
Stages are unique speeds or levels that equipment can operate at. More stages allow for better fine-tuned control of output, which improves comfort and efficiency. Modulating equipment can operate across a range of levels, giving the highest level of fine-tuned control. Learn More
Connection Type
Mount Type
Minimum Altitude
0 Feet
Maximum Altitude
10000 Feet
Includes Pump
Assembly Type
Gas Conversion Kit
AFUE Learn More
AFUE (Annual Fuel Utilization Efficiency) measures the efficiency of combustion equipment over the entire heating season, and is calculated by dividing the amount of energy that is actually heating your home by the total energy contained in the fuel used by the boiler/furnace. Learn More
92 %
Maximum Input Capacity Learn More
Maximum Input Capacity
The Maximum Input Capacity describes how quickly the appliance will use fuel when delivering it's maximum capacity. The units may change depending on the fuel being used.
80000 BTU
Minimum Input Capacity
8000 BTU
DOE Heating Capacity Learn More
DOE Heating Capacity
Also referred to as Gross Output, this is the output of a boiler after accounting for combustion efficiency. We recommend sizing hot water boilers based on the DOE Heating Capacity.
73000 BTU
Net I=B=R Capacity Learn More
Net I=B=R Capacity
I=B=R, also referred to as Net Output or AHRI Capacity, is the rated heat output of a boiler after accounting for combustion efficiency, piping loss, and an extra pickup factor. We recommend sizing steam boilers based on the I=B=R rating.
63000 BTU
Ultra Low NOx Emissions Learn More
Ultra Low NOx Emissions
NOx is a byproduct of the combustion process, and it's output is regulated in some jurisdictions. Many regulators mirror SCAQMD rules, which regulate air quality for some parts of Southern California. Ultra Low NOx appliances emit less than 10-14 ng/J (nanogram per Joule) of NOx. Learn More
Turndown Ratio
Electrical Data
60 Hz
Flue Connection Size
3 Inches
Gas Connection Size
1/2 Inch
Supply Connection
3/4 Inch
Return Connection
3/4 Inch
Product Height
23 5/8 Inches
Product Width
15 3/4 Inches
Product Depth
12 29/48 Inches
Product Weight
70 Pounds
Shipping Weight
80 Pounds
Energy Star Listed
ETL Listed
ASME Certified
AHRI Certified
ISO Certified
AHRI Reference Number
Warranty Information
Parts Warranty Learn More
Parts Warranty
A warranty is a safeguard from defects in manufacturing and can vary in length and terms. To see the manufacturer's warranty statement, click on the Manuals tab. Learn More
2 Years
Heat Exchanger Warranty
10 Years


Williamson-Thermoflo FS-80 COMBI Reviews & Ratings

Product Q&A

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Product Questions Answered by Bob, the Heating Product Expert
Is this a direct hot water heater or an indirect? And will I need a hot water holding tank?
from Pennsylvania 
December 22, 2015
Will the Freestyle work with two heating zones?
from Connecticut 
December 03, 2015

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Williamson-Thermoflo FS-80 - 73K BTU - 92.4% AFUE - Combi Gas Boiler - Direct Vent
Williamson-Thermoflo FS-80 COMBI
Williamson-Thermoflo FS-80 COMBI
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