New Construction Furnace Usage

With the economy slowly turning around, new home construction has started to pick up again — this is good!  Since new home construction is making a come back, it is time to remind everyone about the practice of using the furnace as a “construction heater”.

It is a common practice to use the central furnace as a construction heater during the finishing phases of construction on a new home.  This practice can cause major problems for the appliance.

In all the installation instructions that I have read from manufacturers, they all have this wording in those instructions: THE FURNACE IS NOT TO BE USED FOR TEMPORARY HEATING OF BUILDINGS OR STRUCTURES UNDER CONSTRUCTION. 

Why don’t manufacturers want the furnaces used for temporary heating in new construction?

  1. This practice forces the furnace to operate under unusual and abnormal conditions (ie. very low return air temperatures). Furnaces operating under these conditions can lead to the formation of condensation in the furnace and/or vent system even though the appliance may be a non-condensing furnace under normal conditions.
  2. Using the furnace as a construction heater exposes the furnace to an atmosphere which has the distinct possibility of being corrosive. Typically, in the finishing phases of construction, chlorides from sources such as paint, stain, varnish, tile and counter cements, adhesives, and foam insulation are present in the structure. A corrosive atmosphere combined with condensation is a recipe for trouble.
  3. Often time the return air filter is removed or the furnace is run with the doors off.  This allows “construction dust” to enter the furnace in areas such as the heat exchanger, blower housing and wheel, burner area, and venting system. On 90+% efficient furnaces, the secondary heat exchanger can become plugged on the fins reducing air flow and heat transfer.

If you are going to use the furnace as a “construction heater” then you MUST follow these instructions as we now list in our current installation instructions:


In essence, the furnace must be completely and properly installed with all doors in place.  Before turning the house over to the end-user, the furnace should be completely cleaned and a complete start-up performed on the unit to assure proper operation and that the new owner will be getting an appliance that will be reliable and functioning for years to come.


About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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2 Responses to New Construction Furnace Usage

  1. Nick says:

    A fiend of mine is renovating. He had new furnace put in and the installer told to have the ducts cleaned before use otherwise it will be damaged. My thoughts are why? I would just keep an eye on the filte and clean it when the construction is done. He’s talking about blocking return and vents and using it. I Figure that could cause damage. What do you think?

    • I would suggest you have him read the post. Blocking vents and still trying to operate the furnace will damage it if there is no air movement. If he is blocking them with a filter material or cheesecloth which still allows air movement, he still needs to address the burners and controls.

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