Frequently Asked Questions (FAQs)

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.

Code adoption takes place at the state, and in some cases municipal, level. To determine the code in a particular state, visit the Status of State Energy Code Adoption page.

Yes, in Section 402.4 of the 2012 IECC, testing is now required instead of an option between testing or visual inspection such as in the 2009 IECC.  Also, the air leakage rates changed.

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)

or

(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.

The 2009 IECC requires that a minimum of 50% of the lamps in permanently installed lighting fixtures be high-efficacy lamps (2009 IECC, Section 404.1). The 2012 IECC has increased the minimum percentage from 50% to 75%, along with an exception for low-voltage lighting (2012 IECC, Section R404.1).

REScheck currently does not have a lighting input function; therefore, the lighting requirement should be confirmed under the Requirements Tab in the program.

Both the 2009 and 2012 IECC require duct tightness to be verified. Verification can take place via either a post-construction test or a rough-in test.

For the post-construction test, leakage measurement must be made across the entire system, including the manufacturer’s air handler enclosure, with all register boots taped or sealed at a test pressure of 0.1 inches w.g. (25 Pa). The 2009 IECC limits the leakage to outdoors to less than or equal to 8 cfm per 100 ft² of conditioned floor area or total leakage less than or equal to 12 cfm per 100 ft² of conditioned floor area. The 2012 IECC only contains a requirement for total leakage of less than or equal to 4 cfm per 100 ft² of conditioned floor area.

For the rough-in test, leakage measurement is made across the system, with the manufacturer’s air handler enclosure if it is installed. The test is conducted at 0.1 inches w.g. (25 Pa) with all registers taped or sealed. The 2009 IECC limits leakage to less than or equal to 6 cfm per 100 ft² of conditioned floor area when the air handler is installed and 4 cfm when it is not installed. The 2012 IECC limits the leakage to 4 cfm per 100 ft² of conditioned floor area when the air handler is installed and 3 cfm when it is not installed.

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.

A commercial building is defined as all other buildings that are not considered a residential building.

The term “residential building” includes:

1. detached one-or-two family dwellings having not more than three stories above grade plane;
2. buildings that consist of three or more attached townhouse units and have not more than three stories above grade plane;
3. buildings that are classified in Group R-2, R-3 or R-4 and have not more than three stories above grade plane

Note:  The key point is not the age of the building, but whether it is registered or eligible to be registered and listed.  In the following cases, historic buildings are considered exempt from provisions of the energy code (however, we recommend always confirming with the state or local jurisdiction):

• listed in the State or National Register of Historic Places;
• designated as a historic property under local or state designation law or survey,
• certified as a contributing resource with the National Register listed or locally designated historic district; or
• with an opinion or certification that the property is eligible to be listed on the National or State Registers of Historic Places either individually or as a contributing building to a historic district by the State Historic Preservation Officer or the Keeper of the National Register of Historic Places. 

“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.

• Copies of the International Energy Conservation Code (IECC) can be purchased from the International Code Council website.
• Copies of ASHRAE standards can be purchased from the ASHRAE website.
• For codes specific to a state or municipality, contact the authority having jurisdiction.

We apologize for the issues that you are experiencing with the New Comcheck-Web. The team is aware that the software is having some performance problems when saving and loading data and are working to address the issue and hope to deploy a solution within the next couple months.
If you wish to continue with this version, one thing that could work is saving the information frequently like entering 2-3 values and clicking on save instead of entering a lot of information and then saving. 

Otherwise you can also use the Legacy COMcheck Web version (can be accessed on energycodes.gov) which does not have this issue. You will be required to register a new account. Unfortunately, because the New COMcheck-Web uses a different project structure than the Legacy COMcheck-Web, we don't have a way to export project data from the New COMcheck-Web and import it into the Legacy COMcheck-Web. If you choose to use the Legacy COMcheck-Web, the best way is to start a new project. 

If you are using a new energy code (like 90.1 2022 or 2024 Minnesota Energy Code) which is available only in the New COMcheck-Web, Legacy-Web version cannot be used. In such cases, you might want to try saving information in your project after some time or create a copy and see if you are able to save information in the duplicate project. 

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. 

The problem most likely relates to the basement walls you have specified. The DOE-2 simulation program used in REScheck for performance alternative calculations sometimes generates this error even though the entries appear valid.

As a workaround, we recommend that you split your basement walls so that for each basement wall you add a new above-grade wall to represent the above-grade area of the basement wall. 

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.