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How to Pass Load Calc Requirements for a Permit
By Chris Morin - HVAC Pro Blog

There is nothing more frustrating in the HVAC trade than not knowing permit fees, expectations, or even code requirements that seem to be rarely enforced unilaterally across municipalities.

Based on conversations with Building Code Inspectors in MA, there is nothing more frustrating to them either! Sometimes, the perception is that the Code Official is ‘out to get me’, but typically this couldn’t be further from the truth! What I usually find is the HVAC Contractor does not know, what they don’t know.

So, let me save you the trouble of failed permit applications, arguments, and appeals. This is what you should be providing for information which must be accurate:

Print the Property Card (Town Assessor)
This is so simple, and will set you up for success. If your load calculation software does not provide a floorplan, this will easily show the code official the layout. I recommend using a ruler and drawing in the interior walls, dimensions of the room, locations of windows, etc. Don’t go overboard, they probably will not need this to scale!

Design Temperatures
This is another 'black and white' check in the box. Your internal design conditions must match recommendation in International Residential Code (IRC) and the International Energy Conservation Code (IECC). Your Outside Design Conditions must match the Manual J Table 1A/1B for the closest weather data city.

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Walls, Ceilings, & Fenestration
Obviously, we are expecting the exterior walls and ceilings dimensions to match the floor plan on the property card. Speaking with code officials, being exact on the square footage is not necessary, but a range of +/- 5% is ‘believable’. If you are using a form style load calculation software, like Elite Software, marking these dimensions on the floor plan for submission with the permit will definitely aide in the building department’s approval process.

Wall & Ceiling construction, materials, and insulation should match the typical material vintage (or what is actually on site).

Glass surface area, type, frame material, shading, and direction should be as close to exact as possible to accurately calculate the cooling gain of the building.

Something so simple, yet easy to confuse, is the direction each wall and window/door faces. I have a bad habit of not noting this during the site survey, and have come to rely on Google Maps to remind me which direction the front door faces (to orient the rest of the home).

Internal Gains
When thinking internal gains, most Contractors immediately think of number of occupants. This is simple, as the number of people is the total number of bedrooms + one (assuming two in the Master Bedroom).

Equipment Loads tend to make up much more of a total for the building. If you are using any adjustments above the three scenario options made available, justification for these additions must be made (i.e. above average lighting load, unvented stove/dishwasher, ceiling fans, etc.). Honestly, anything more than Scenario Two: 2,400 but/hr will need justification in most municipals.

Duct Conditions
Ductwork location, insulation, sealing, and surface area can significantly impact the load. The duct condition is one of the major differences in using Manual J v8 compared to the out of date v7. A poorly insulated, unsealed, trunk and branch duct system located within an unvented attic can contribute as much as 1/2 ton or more to the Cooling gains. That same duct system in a basement could impact the latent gains enough to alter the size of the system as well. Is all of your ductwork within the conditioned space, or using ductless equipment? Then you will have a smaller system with zero losses or gains on that metal.

New Duct System? Expect the need for Manual D Friction Rate Worksheet, Duct Sizing Worksheet, and sketch showing sizes of trunks runs.

I hope this helps set some basic expectations with your next permit application. Providing the above details, and having them be correct, will go a long way for your successful process and inspection.

P.S. If you don’t know how to identify all of the above - I provide training for this!

About HVAC Pro Blog
In 2012, while working as a Tech Instructor for a Utility Rebate Program Implementer, I realized I had a lot more to share about my experience in the HVAC Industry than just what my classes were providing an outlet for. Since my first readers were mostly Technicians, I began writing about the Heating and Cooling service topics I was known for locally. As my role in the industry changed, and I met with more Salespeople and Business Owners, I expanded my content to include System Design and Business topics.

I am excited to work on exclusive content for my Patreon Partners; developing the new content, training, and support you need and influence. HVAC Pro Blog provides advice for Residential System Design, Quality Installation, and System Diagnosis.


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