Why on earth are we doing a Manual J or a Manual D or a Manual S Anyway?
Many local codes now require Manual J and Manual S load 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 load 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 over 25 years 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
The Right Fit
A Manual J heat load calculation is like getting properly fitted footwear at a quality shoe store. Running a heat load is like the sizing of your foot. The Manual S procedure is like the selection of the proper footwear. There is more to the process than grabbing a pair of shoes off the shelf and having the sales associate scan the barcode and process your credit card. Just like the footwear, if you don’t get the proper fit, not too big, not to small but just right, you will probably never feel right.
The Manual S procedure guides us through the complex process of selecting the proper size equipment that enables us to get the right fit. If the HVAC equipment installed in your home is over-sized by more than about 15% of the calculated heat load, then you are likely to experience improper humidity control , uneven temperatures and short cycling of your equipment which leads to premature equipment failure.
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.