Manual J Design Studio

Manual J HVAC Load Calculations

Manual J Design House Plans
Executive Summary

Tradewinds Appropriate Technologies is a third party licensed Heating, Ventilation and Air Conditioning (HVAC) company that specializes in HVAC system design, analysis, validation and troubleshooting.

We have over 15 years of experience performing Manual J load calculations and are considered by some to be among the top HVAC system designers in the country.

We have written 12 HVAC continuing education courses over the last 7 years. These courses focus on system design, ventilation and dehumidification with a special emphasis on foam homes.

Custom load calculations conducted by an experienced third party like Tradewinds’ Manual J Design Studio will equip you with a design that will provide a comfortable, energy efficient living experience.

Tradewinds is also an approved training provider for Elite Software. Thank you for your interest in Tradewinds’ Manual J Design Studio. Please read on for important information concerning who we are and how we can contribute to your success.

Manual J Design Studio
Air Conditioning System Design for Homes

Company Overview

Tradewinds Appropriate Technologies is a third party, licensed Heating, Ventilation and Air Conditioning (HVAC) contracting firm specializing in residential and light commercial HVAC system design. As a third party, we don’t install or repair equipment; we simply provide quality assurance for HVAC and spray foam contractors by designing and testing systems from an independent, unbiased perspective.

HVAC System Design Experience

We design HVAC systems using Air Conditioning Contractors of America (ACCA) approved Manual J load calculation, Manual S system design and Manual D duct design software. We began performing computer-based load calculations over 15 years ago. Our senior designer and training instructor, Paul Wieboldt, has written and taught more than 12 different HVAC continuing education courses to licensed HVAC contractors over the last seven years. These courses focus on the basics of system design, duct design, mechanical ventilation and dehumidification with special emphasis on the proper design of HVAC systems for foam homes. In fact, Tradewinds initiated the dialog and worked directly with the engineers at Elite and ACCA to incorporate foam insulation into the design calculations and add spray foam walls and roofs to the list of building materials. Tradewinds also helped introduce the calculation for ventilation based on infiltration rates. Tradewinds is considered by other industry professionals as a Manual J “power user”. Some of our staff members are among the top HVAC system designers in the country.

Experience in the Spray Foam Industry

In 2005, Tradewinds bought and refurbished a spray foam machine. We attended manufacturer training, sprayed a few homes and learned the process, specifically focusing on what it takes to do a first quality job. As the number of spray foam contractors significantly increased in our service area, we found we could better serve our customers by focusing on system design and performance testing of building envelopes, insulation and HVAC systems. The insight we gained from this experience was invaluable. We are now able to design HVAC systems for foamed homes based on real life experience.

Energy Star HERS Rater Expert Staff

Since 2003, Tradewinds has certified ENERGY STAR™ homes. That experience evaluating the performance of the building envelope has helped us fine tune the HVAC equipment selection and mechanical ventilation to optimize home performance.

The “Go to Guys”

Years of providing consistently accurate, fair and balanced testing, reporting and problem solving have earned Tradewinds a reputation as the “go to guys” for new and existing home design issues.

Purpose of Custom Load Calculations

Many local codes now require Manual J and Manual S calculations for every new home and remodel that changes the load of the house. The fact is, very few contractors know how to properly execute either calculation. Although advances in building insulation are rapidly changing the profile of the average American home, the typical HVAC contractor still selects an air conditioning system for a home based on the old rule of thumb of 500 sq. ft. per ton. Unfortunately, most contractors are afraid to change this long habit of ‘guesstimating’. This ‘fear factor’ holds many contractors in design paralysis. In a new home, this practice can have disastrous consequences. As the building envelope is made more efficient and the effective R-value is dramatically increased by the use of spray foam and other high efficiency insulation measures such as SIPs, ICF and dense pack cellulose, the size of the air conditioning equipment should logically decrease. A well-constructed high-efficiency building envelope can and does change the rules. Our years of experience indicate that when properly assembled, a super efficient home can be cooled with an A/C unit as little as half the size of one used to cool a conventional home. Consequently, many HVAC contractors mistakenly install oversized equipment in high efficiency homes. We’ve received phone calls from building contractors asking us to do Manual J load calculations for them. Some of their customers are complaining that it’s “raining in their house.” This is clearly not the fault of the insulation application. It is the responsibility of the HVAC contractor to properly match equipment to the heat load of the house, design in the necessary dehumidification functions and to provide adequate mechanical ventilation for today’s tighter, more efficient homes. With our nearly 2 decades of HVAC design and installation experience, we can guide the HVAC contractor involved with your projects to the safe efficient solution.

More than Manual J designers, we are masters of Manual S

Over-sizing is a very real problem, but it isn’t the only problem. Design professionals must also understand the principles of Manual S regarding equipment selection. It is an all too common mistake when completing a load calculation alone to miscalculate the equipment size. Many designers attempt to take the results of a Manual J calculation and erroneously assume that the heat load estimate for the house is the recommended equipment size. They further compound the error by assuming that the nominal capacity of HVAC equipment is equal to its actual installed output.

Bull’s Eye!

To use an analogy, the results of a Manual J load calculation are like a target with a big red bull’s-eye on it. The Manual S procedure helps us to select the proper bow and matched arrow that enable us to hit the bull’s eye every time. Tradewinds has mastered the art of properly sizing equipment for any location, nation-wide, by considering local ambient design temperatures and making the correct adjustments to equipment cooling capacities so that a perfect match is selected every time.
Custom load calculations conducted by an experienced third party like Tradewinds’ Manual J Design Studio will equip you with a design that will provide a comfortable, energy efficient living experience.

Professional Contractor Services:

Tradewinds serves as a national third party HVAC system design firm. To offer consistency across the nation, Tradewinds is equipped to serve all of your projects by performing all of the Manual J load calculations needed. We believe our expertise in HVAC system design will enhance the value of your products and contractors’ services by ensuring the right sizing of HVAC equipment for every home. As mentioned, Tradewinds is also an approved training provider for Elite Software. Training is available at our Texas Training Center.
We are also available to conduct regional training for your contractors as needed. Please contact Paul Wieboldt for further information about our professional contractor services and preferred customer rates ( or 888-799-1326).

To get started with a custom design for your project, contact us at:

Important announcement concerning humidity!

If you have a tightly built house in East, Central, South, South Central or North Central Texas, you need to talk to us about humidity and dehumidifiers. According to ASHRAE, high efficiency air conditioners might not remove humidity adequately in our climate in a tightly built house.

Two vital elements of air conditioner design are the ACCA Manual J load calculation and the ACCA Manual S Equipment Selection. These are so important that they were mandated in the 2009 IRC building code.

These design procedures are vital for spray foam, ICF and SIP homes, but they are even necessary for homes built to the ENERGY STAR™ guidelines or even to the new IECC codes.

If you feel warm or clammy when the thermostat says you should be cool and comfortable, check your humidity levels. Go to the Air Quality page for a discussion on humidity.

Remember, ventilation alone is not enough in our climate!

Important announcement concerning
spray foam, SIP or ICF Homes

We have seen that designers do not realize that the new super-insulated homes cause a strange phenomenon in Texas.

Builders do not primarily design for heating loads in Texas. However, the super-insulated homes with a slab floor need to take into account the heating load of the slab. The slab becomes the largest energy hog in these homes. The designer needs to specify an insulated slab to overcome this problem.

Call or write us for more information.

Manual J Design Studio

a division of

Tradewinds Appropriate Technologies, LLC