Frequently Asked Questions (FAQs)

In COMcheck 4.0.0.3 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.

REScheck uses nominal insulation R-values. The program does not calculate for compression. For example, if R-19 is entered as the cavity insulation R-value, it assumes the full R-19 in REScheck. Walls with insulation R-values equal to or less than R-15 are modeled in REScheck as having 2x4 studs at either 16" or 24" O.C. (on center) and cavity wall insulation R-values greater than R-15 are modeled as 2x6 studs at either 16” or 24” O.C. 

For more detailed information on how the walls are calculated please refer to the REScheck Technical Support Document.

Exterior walls in REScheck are defined by the assembly type, gross wall area, cavity/continuous R‑value (U-factor for Other walls) and orientation.  All exterior walls are assumed to be of regular rectangular shape with an average wall height of 9 ft., and the wall width is calculated from the gross area as input by the user. 

REScheck wall materials are assumed to be plywood siding, plywood structural sheathing, and foam insulation sheathing on the framing exterior, batt insulation, wood framing, and 1/2-in. gypboard on the interior.  The entire wall is assumed to have structural sheathing. When continuous foam insulation is specified, 100% of the wall is assumed to be covered at the specified R-value.

The U_o‑factor for all frame walls is based on the R‑value of cavity insulation and the continuous insulation R‑value (if used).  If the user does not enter a continuous insulation (sheathing) R‑value (or enters a value of 0.0), the software assumes a sheathing R‑value of 0.83.  This default value gives credit for some minimal type of sheathing material (such as plywood) under the siding. 

Continuous Insulation

Insulation that runs continuously over structural members and is free of significant thermal bridging; such as rigid foam insulation above the ceiling deck. It is installed on the interior, exterior, or is integral to any opaque surface of the building envelope.

Cavity Insulation

Insulation installed between structural members such as wood studs, metal framing, and Z-clips.

Cavity insulation is used within the wood- or metal-framed wall, while rigid continuous insulation (c.i.) is placed on the exterior side of the framing.  Alternative combinations of cavity insulation and sheathings in thicker walls can be used, provided the total wall assembly has a U-factor that is less than or equal to the appropriate climate zone construction requirements.

Cavity Insulation Calculation in REScheck

REScheck uses nominal insulation R-values. The program does not calculate for compression. For example, if R-19 is entered as the cavity insulation R-value, it assumes the full R-19 in REScheck. Walls with insulation R-values equal to or less than R-15 are modeled in REScheck as having 2x4 studs at either 16" or 24" O.C. (on center) and cavity wall insulation R-values greater than R-15 are modeled as 2x6 studs at either 16" or 24" O.C. 

Continuous Insulation Calculation/Insulated Sheathing

The assemblies listed in REScheck already have a default value added for standard sheathing (depending on the assembly component). If no sheathing is indicated by the user, the sheathing is assumed to be plywood with an R-value of 0.83. If insulated sheathing is used, only 80% of the net wall is assumed to be covered by the insulated sheathing. The other 20% is assumed to be covered with plywood.

REScheck Quick Tip

Cavity R-Value - Enter the R-value of any insulation to be installed in the cavities between above-grade wall structural members. The insulating values of other parts of the building assembly (e.g., gypsum board and air films) are accounted for by the program and should not be included.

REScheck  wall assemblies assume cavity insulation completely fills the cavity.  Users who have unique wall assemblies where the cavity is not completely filled with insulation must account for the air space within their wall assembly calculation and should use “other” as the wall type and enter their respective overall calculated U-factor.

Continuous R-Value - Enter the R-value of any continuous insulation in the above-grade wall. Continuous insulation is continuous over framing members or furring strips and is free of significant thermal bridging. The R-values of other parts of the building assembly (e.g., gypsum board and air films) are accounted for by the program and should not be entered. Insulated sheathing installed on the exterior of above-grade walls is an example of continuous insulation. For structural insulated panels and insulated concrete forms, enter the manufacturer-reported R-value for the entire assembly.

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

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. 

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.

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.

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.

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.   

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. 

“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.

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.

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. 

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.

Yes.

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.

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.