Frequently Asked Questions (FAQs)

Can I share my saved lighting fixture library on another computer?


  1. Locate the lighting fixture library in this location defaulted by COMcheck:   
    C:\Users\<your user name>\AppData\Roaming\COMcheck\fixtureLibrary.xml.
  2. Copy fixtureLibrary.xml from this location to the same directory on the other computer.
Are projects required to be completed by a registered design professional?

The commercial energy code requires that a registered professional submit compliance documentation (construction documents and compliance verification).    In the IECC, Section C103.1 Construction Documents, General, the wording states that construction documentation and other supporting data shall be submitted in one or more sets with each application for a permit.  The construction documents shall be prepared by a registered design professional where required by the statutes of the jurisdiction in which the project is to be constructed.  Where special conditions exist, the code official is authorized to require necessary construction documents to be prepared by a registered design professional.

The definition in the code for a registered design professional is:  an individual who is registered or licensed to practice their respective design profession as defined by the statutory requirements of the professional registration laws of the state or jurisdiction in which the project is to be constructed.

As for COMcheck, there are no requirements as to who can use it and who can create a compliance report, but as to who signs and submits the report, the requirements stated above should be followed.

Can you combine two data files into one project?

Unfortunately, there is not a way to merge files.  The web tool is definitely the way to go when you have multiple contractors involved as you can create a generic log in and each contractor can work on the same project file to enter their information (e.g., building envelope, lighting, mechanical). 

Project sharing will soon be more user friendly. 

Do electric central furnaces qualify for the High Performance HVAC Efficiency package in the 2012 IECC?

Electric central furnace does not qualify for the High Performance HVAC efficiency package. ALL systems in a project must meet the criteria of C406.2 and if your system(s) cannot be found in C406.2 then by default it does not qualify. In these cases if you want to use the electric central furnace then you have to choose a different additional efficiency package.

The following is the code section that enforces this:

C406.2 Efficient HVAC performance. Equipment shall meet the minimum efficiency requirements of Tables C406.2.(1) through C406.2(7) in addition to the requirements in Section C403. This section shall only be used where the equipment efficiencies in Tables C406.2(1) through C406.2(7) are greater than the equipment efficiencies listed in Table C403.2.3(1) through 403.2.3(7) for the equipment type.

When entering doors in COMcheck, do I use "operable U-factor" or "caclulated U-factor?"

“Standard 90.1 requires that U-factors (and air leakage) for doors be determined in accordance with the NFRC rating procedures.  All NFRC ratings are based on the whole product, including the frame.”

Consequently, for compliance with Standard 90.1, door U-factors must be:

  • either determined in accordance with NFRC 100 or
  • assigned the default values in Section A7.1.

Both the NFRC 100 and the Section A7.1 values are for the overall door area, including the door slab and the door frame.

In the same way that some window manufacturers only refer to the center of glass performance (and to ignore the thermal bridging through the window frame), door manufacturers have preferred to talk about the door slab only (and to ignore the thermal bridging in the frame).  However, Standard 90.1 requires whole product ratings in accordance with NFRC 100.  

The bottom line from a strict 90.1 and IECC perspective is that if the U-factor is not developed using NFRC 100, the default values in Standard 90.1 must be used.  These defaults are available in COMcheck and can be used.  They represent very poorly performing doors, which can be an issue for some buildings if the door area is a significant fraction of the wall area.

Why won't the report print?

The file is saved but I cannot get a pdf or rtf file to print.

There are a couple of things to try:

  1. Completely remove REScheck or COMcheck

    • Use the Windows operating system “Programs and Features” uninstaller
    • Open Windows Explorer and navigate to C:\Users\<your username>\AppData\Roaming\<REScheck or COMcheck>
    • Delete the check.prp and defaults.dat files
    • Navigate to the REScheck or COMcheck application folder:  C:\Users\<your username>\AppData\Local\Check\<REScheck or COMcheck>
    • Delete all of the contents of this folder, including any sub-folders
      (These steps should ensure the application has been fully removed.)
    • Then try reinstalling REScheck or COMcheck
  2. If that doesn’t work, use the web tool which requires no download but you will want to register so you can save your projects.   
How does the importing of a gbxml file option function?

There are a couple things to note about the current import process implementation:

  • Currently we only focus on importing envelope components. This means you will still be required to manually specify your space types, lighting fixtures, and mechanical systems that appear in your building.
  • Depending on the size of your building, a gbXML file can potentially contain thousands of surfaces to fully represent your structure. Working with that many envelope components in COMcheck is unreasonable, which is why we identify surfaces with similar characteristics and aggregate them during the import process.
Is thermal bridging taken into account and any other parts of a wall assembly such as the girts, z clips, framing members, etc.?

COMcheck does account for thermal bridging of framing members, furring, etc. (depending upon the assembly). U-factor assembly calculations are taken from ASHRAE Appendix A and ASHRAE Fundamentals. The methodology used to calculate compliance is taken from ASHRAE Appendix C. When an assembly is chosen from the drop down lists in the program, there is a U-factor automatically displayed for that assembly (excluding fenestration). Once the user enters the proposed insulation R-value(s) for the assembly, the program recalculates the assembly and updates the U-factor to the overall U-factor for the entire assembly. Also users have the option to choose "other" as the assembly type. If “other” is selected, the user will then need to enter the overall calculated U-factor for the entire assembly and document those calculations to the building official.

What do I use if my city is not listed?

Choose a city that is the closest with the most similar weather.  Check with the building official where the project is located to confirm the city selected will be acceptable or if choosing “county” as the designation would be more appropriate.  The easiest way to choose county would be to use the web tool which has the option between city and county on the project tab screen.

How are louvers identified in COMcheck?

Louvers are best treated as un-insulated portions of the wall. You can add them as a separate wall type (for example, if they are metal, metal building would probably be most appropriate) with no insulation but a wall area. COMcheck will do the area-weighted averaging for the opaque wall to calculate the overall U of the opaque wall. The impact of having an uninsulated wall area is that you will be required to “make up for that” in some other portion of the building envelope. This may mean more insulation on the rest of the wall, better windows, or more roof insulation.

Note:  There is an allowance for up to 1% of wall area in “recessed equipment” in walls in Standard 90.1 if 90.1 is the code in which you are complying with. 

How do I enter VRF Systems into COMcheck?

In COMcheck and newer, you can now break up your VRF into two systems.  One can be defined as the VRF Outdoor/Central unit and is selected as heating equipment→heat pump list-→"VRF xxxx". This type of system will enforce the system efficiency depending on the system cooling capacity.

If the economizer requirement is enforced you can select the economizer exception "VRF Outdoor/Central Unit". The other VRF system you would specify is from the cooling equipment side of the HVAC systems dialog and is called "VRF Zone Fan Unit". If you select this as your system the capacity of individual units will generally be so small that the economizer requirement will not be enforced. And the system efficiency is also not enforced as there is no efficiency requirement for this part of the VRF system.

Notes: If you don't find the VRF system available in the HVAC system dialog then it is probably due to the energy code you have selected. Some energy codes don't enforce compliance with VRF systems. 2009 IECC and 90.1-2007 are 2 of them. If VRF isn't found in the energy code being used it is because it is not enforced by that energy code.

What are space conditioning types?

ASHRAE’s space conditioning types include: conditioned space, unconditioned or semi-heated space. ASHRAE’s definitions for these types:

space: an enclosed space within a building. The classifications of spaces are as follows for the purpose of determining building envelope requirements.

(a) conditioned space: a cooled space, heated space, or indirectly conditioned space defined as follows.

1. cooled space: an enclosed space within a building that is cooled by a cooling system whose sensible output capacity exceeds 5 Btu/h*ft2 of floor area.

2. heated space: an enclosed space within a building that is heated by a heating system whose output capacity relative to the floor area is greater than or equal to the criteria in Table 3.1.

3. indirectly conditioned space: an enclosed space within a building that is not a heated space or a cooled space, which is heated or cooled indirectly by being connected to adjacent space(s) provided:

(a) the product of the U-factor(s) and surface area(s) of the space adjacent to connected space(s) exceeds the combined sum of the product of the U-factor(s) and surface area(s) of the space adjoining the outdoors, unconditioned spaces, and to or from semi-heated spaces (e.g., corridors)


(b) that air from heated or cooled spaces is intentionally transferred (naturally or mechanically) into the space at a rate exceeding 3 air changes per hour (ACH) (e.g., atria).

(b) semiheated space: an enclosed space within a building that is heated by a heating system whose output capacity is greater than or equal to 3.4 Btu/h*ft2 of floor area but is not a  conditioned space.

(c) unconditioned space: an enclosed space within a building that is not a conditioned space or a semiheated space.

How does COMcheck calculate percentage of glazing?

COMcheck implements the calculation based on the definition of above and below-grade walls in the applicable code.  The calculation for percentage of glazing in ASHRAE Standard 90.1 and the IECC are different as the IECC only looks at above grade walls and 90.1 includes both above and below grade walls.

From ASHRAE 90.1-2010

5.5, Prescriptive Building Envelope Option, provided that 

  1. the vertical fenestration area does not exceed 40% of the gross wall area for each space-conditioning category

wall: that portion of the building envelope, including opaque area and fenestration, that is vertical or tilted at an angle of 60 degrees from horizontal or greater. This includes above- and below-grade walls, between floor spandrels, peripheral edges of floors, and foundation walls. For the purposes of determining building envelope requirements, the classifications are defined as follows:

above-grade wall: a wall that is not a below-grade wall.

below-grade wall: that portion of a wall in the building envelope that is entirely below the finish grade and in contact with the ground.

wall area, gross: the area of the wall measured on the exterior face from the top of the floor to the bottom of the roof.

From 2012 IECC:

C402.3.1 Maximum area. The vertical fenestration area (not including opaque doors and opaque spandrel panels) shall not exceed 30 percent of the gross above-grade wall area.

Can I show compliance using COMcheck if my glazing is over the 40% threshold in the 2009 IECC?

The Scope and Application sections of the 2009 IECC address use of ASHRAE 90.1 (2007) as an alternative.  See below for the text.  It is appropriate to use ASHRAE 90.1 as an alternative when your building exceeds 40% glazing, although it does not guarantee your building will comply.  ASHRAE offers an exception to the 40% limitation that calculates the partial shading provided by permanent opaque projections (Refer to ASHRAE 90.1-2007 Sections and, Exception (b)).

501.1 Scope.  The requirements contained in this chapter are applicable to commercial buildings, or portions of commercial buildings.  These commercial buildings shall meet either the requirements of ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except for Low-Rise Residential Buildings, or the requirements contained in this chapter.

 501.2 Application.  The commercial building project shall comply with the requirements in Sections 502 (Building envelope requirements), 503 (Building mechanical systems), 504 (Service water heating) and 505 (Electrical power and lighting systems) in its entirety.  As an alternative the commercial building project shall comply with the requirements of ASHRAE/IESNA 90.1 in its entirety.  Exception:  Buildings conforming to Section 506, provided sections 502.4, 503.2, 504, 505.2, 505.3, 505.4, 505.6 and 505.7 are each satisfied.

Why am I receiving an error message that the check envelope compliance simulation failed?

When using the ASHRAE 90.1-2013 energy code, COMcheck needs to have two EnergyPlus weather files in this folder C:\ProgramData\COMcheck\eplus\weather. The most common reasons for a compliance simulation failure are: 

  1. the files are not located at this default location
  2. only one file is there instead of the two needed
  3. the files are of a different size than anticipated.

The two weather files will have names and file sizes similar to these (of course the file names will reflect your building’s project location):

  • USA_NJ_Newark.Intl.AP.725020_TMY3.epw (~1,619 KB)
  • USA_NJ_Newark.Intl.AP.725020_TMY3.ddy (~29 KB)

What to do if you get this error:  Delete one or both weather files and attempt to run simulations again so that the weather download process gets executed again.

How it works:  If these weather files are not found at the expected location (C:\ProgramData\COMcheck\eplus\weather), COMcheck will attempt to download them. 

NOTE:  Once these weather files are downloaded they will remain on the PC at C:\ProgramData\COMcheck\eplus\weather.  Therefore, the weather download process only needs to execute one time per unique project location. Obviously for this process to work the current user must have user privileges that permit COMcheck to establish an internet connection and to download these files. 

Is there code language that allows the use of COMcheck?

The COMcheck trade-off alternative used for enforcing the IECC is permitted under a clause in Section 101 (referencing 2012 IECC). That clause is a fairly common code element that gives the jurisdiction and, more explicitly, the building official the latitude to allow any compliance approach that "makes sense" with respect to accomplishing the code's objectives. This kind of clause is often referred to as a "deemed to comply" approach. Through legislative and/or legal procedures, jurisdictions agree and accept to adopt this provision when adopting the IECC editions and in many cases amend the adopted code to explicitly include language that expressly permits use of the COMcheck software.

Specifically, Section 101 allows a building official to approve compliance tools that are deemed to meet "the intent of [the] code." The intent of the IECC commercial code is explicitly defined here: "C101.3 Intent. This code shall regulate the design and construction of buildings for the effective use and conservation of energy over the useful life of each building. This code is intended to provide flexibility to permit the use of innovative approaches and techniques to achieve this objective." The various compliance paths of the code are alternative "recipes" designed to achieve that intent, but Section 101 implies that other recipes are permitted if they accomplish the same overall objective.

The trade-off methodology used by COMcheck is consistent with the "Normative Appendix C: Methodology for Building Envelope Trade-Off Option" found in the referenced ASHRAE 90.1 code. However, to determine compliance with an IECC edition, all IECC requirements are applied to and enforced within that trade-off methodology including Section C402.3.1 "maximum fenestration and skylight area" (COMcheck restricts users from using the trade-off approach when the C402.3.1 provisions are not met, redirecting them to use of the referenced 90.1 as allowed by C401.2).

The IECC explicitly references what version of ASHRAE 90.1 corresponds with IECC sections on page C-78 of the 2012 IECC.

Codes: 2009 and 2012 IECC, ASHRAE Standard 90.1-13/2015 IECC

The 2009/2012 editions of the IECC (commercial provisions) do not include language explicitly describing a defined envelope trade-off compliance method. Only a set of prescriptive envelope requirements are provided. However, Section 101 of the IECC has a clause that has been widely interpreted and understood to give a building code official or jurisdiction the latitude to allow any compliance approach that "makes sense" with respect to accomplishing the code's objectives. This kind of clause is often referred to as a "deemed to comply" approach. Through legislative and/or legal procedures, jurisdictions agree and accept to adopt this provision when adopting the IECC codes.

Specifically, Section 101 allows a building official to approve compliance tools that are deemed to meet "the intent of [the] code." The intent of the IECC commercial code is explicitly defined here: "C101.3 Intent. This code shall regulate the design and construction of buildings for the effective use and conservation of energy over the useful life of each building. This code is intended to provide flexibility to permit the use of innovative approaches and techniques to achieve this objective." The various compliance paths of the code are alternative "recipes" designed to achieve that intent, but Section 101 implies that other recipes are permitted if they accomplish the same overall objective.

Excepting COMcheck support for 90.1-2013 and 2015 IECC, the envelope trade-off methodology used by COMcheck is the "Normative Appendix C: Methodology for Building Envelope Trade-Off Option" found in the referenced ASHRAE 90.1 code. The ASHRAE Appendix C trade-off method does include a limited number of “embedded” references to ASHRAE 90.1 based “prescriptive” requirements that must be enforced. Obviously, these prescriptive requirements are specific to ASHRAE 90.1 section numbers and thus relevant to the IECC codes. For this reason, and that it is only the “trade-off method” that is being “borrowed” for use with the IECC requirements, these Appendix C embedded requirements are not considered when this method is applied to the IECC codes in COMcheck. When applied to the IECC energy codes, all IECC code requirements are applied and enforced within that trade-off methodology when a clear and obvious reference can be established. More specifically, this applies to the table references to individual envelope assemblies U-factor requirements. 

The “embedded” Appendix C requirements discussed in the previous paragraph pertain to maximum window (WWR) and skylight (SRR) areas and minimum skylight area. When determining compliance to one of the ASHRAE 90.1 energy codes, COMcheck will enforce the WWR and SRR per guidance from Appendix C. However, the minimum skylight area requirement as described in Appendix C is worded and interpreted in such a way as to be deemed not applicable therefore is not enforced in COMcheck for either 90.1 or IECC energy codes. When determining compliance to one of the IECC codes the minimum skylight requirement will be enforced through the envelope report inspection checklist and the WWR and SRR requirements will be enforced prescriptively. That is, when complying with IECC and the WWR and SRR values are found to be noncompliant the user will be directed to use the equivalent ASHRAE 90.1 energy code.

To summarize, when the Appendix C trade-off method is applied to IECC codes, the IECC requirements will be applied to the method when and where that method provides guidelines for doing so. When guidelines are not provided by the trade-off method language or refers to nonexistent section numbers, the IECC requirement will be enforced prescriptively. As noted above, ASHRAE 90.1-2013 and 2015 IECC energy codes are exceptions to all of this discussion. ASHRAE 90.1-2013 Appendix C supports a trade-off method that is based on building performance simulations using EnergyPlus completely differently than earlier versions of the 90.1 code family. Only 90.1-2013 uses this method currently although 2015 IECC does allow a project to apply 90.1-2013 in its entirety as an alternative. 2015 IECC Component Performance Alternative is used for 2015 IECC and state codes based upon this code. This new compliance method replaces the use of ASHRAE 90.1 Appendix C and is based generally speaking on a “Total UA” approach.

How do I enter fenestration that does not have a NFRC Product ID?

When entering your fenestration in COMcheck the pop up window has three options to enter your fenestration.  Choose the second option called Product Performance in accordance with NFRC.  If you do not have a pending product number, enter NA and enter your proposed values.  Note, test results should be submitted with the COMcheck report to verify the values entered.

 If the product has not been tested or accredited, choose option 3.  The code defaults come directly from the tables within the code.  Code defaults use worst case scenario for fenestration values and most defaults do not meet the prescriptive requirements dependent upon climate zone. Best recommendation is to choose fenestration products that are tested and NFRC labeled that have better U-factor and SHGC ratings.  

How does COMcheck calculate compliance for the building envelope?

COMcheck computes an envelope index that is a reflection of the difference between a 'design' building energy performance factor (EPF) and a 'code' or budget building EPF.  The total building load (made up of cooling, heating, lighting, and miscellaneous plug load) is determined by the location you are in, the specific assembly and building types you specify, and internal gains from lighting and miscellaneous plug loads, and of course the thermal properties and orientation of the envelope assemblies. The methodology used to determine EPF is provided in ASHRAE 90.1 Normative Appendix C: Methodology for Building Envelope Trade-off Option.

How does COMcheck show compliance for additions or alterations?

COMcheck determines compliance for additions in the same manner as new construction. When entering an addition, only the new portions of the building need to be shown in the software. COMcheck will perform trade-offs between envelope assemblies when determining compliance.

COMcheck determines compliance for alterations on a component-by-component basis. Each component is checked to verify it meets or exceeds the minimum prescriptive requirements of the selected code. No trade-offs are available for alterations and no compliance percentage will be generated–the software shows a pass/fail for compliance.

How are lighting exemptions and allowances shown in COMcheck?

Exemptions and allowances for lighting are an option that must be activated in COMcheck. To activate the exemptions and allowances, take the following steps:

  • Select either the Interior Lighting or Exterior Lighting Tab
  • Go to the Options menu and select Interior Lighting Exemptions and Allowances for Interior Lighting or Exterior Lighting Exemptions for Exterior Lighting.

Note that activation of the exemptions and allowances will add an extra column to the applicable worksheet–it may be necessary to enlarge the window in order to see the new column.

Can compliance be shown for only one area in COMcheck (Envelope, Lighting, or Mechanical)?

If multiple users are putting information into COMcheck, each may fill out the appropriate section independently. However, all sections of the building must show compliance to the same code or standard (e.g., cannot show envelope compliance to IECC and lighting compliance to ASHRAE Standard 90.1). COMcheck does not require that all sections be completed to perform compliance checks.

How are spandrel or translucent wall systems input in COMcheck?

Fenestration is considered anything that transmits light, however, COMcheck cannot calculate fenestration without having a wall associated with it. In this case the wall is entirely fenestration therefore, the square footage would be the same for both the wall and window area and the software will calculate the wall area as net zero since the fenestration is the entire wall.

For the spandrel glass or translucent wall systems the way to enter that into COMcheck would be to first define a wall by choosing wall as "other" from the drop down list of wall assembly types, enter the square footage of the wall system (e.g. 100 sq. ft), enter the U-factor for the wall system (e.g. 0.23) and also you will need to enter the heat capacity of the wall. For information on heat capacity and how to calculate it, in COMcheck, go to the help menu, help topics and wall software inputs.

After defining the wall, define the window area by choosing window as "other" from the drop down list of window assembly types, enter the square footage of the wall system (e.g. 100 sq. ft.) and choose option two under Fenestration details "Product performance tested in accordance with NFRC", if you do not have a product ID, enter "NA", then enter your U-factor and SHGC values from the product manufacture specifications.