When you request quotes from your prospective HVAC contractor, do they ask for a full set of architectural and structural plans? Do they ask for the thermal performance of the actual windows being installed (U-factor & SHGC)? Do they ask what direction the front door of the house faces? How about how many feet below grade the lower level walls will be or how tight your building’s envelope will be? These are just a few examples of the types of questions that have to be answered to be able to properly size your HVAC systems and design an appropriate duct layout. Yes, some of this information may be included on your plans but how often do your specifications change after the architectural plans have been completed?

How can you have confidence that the system being installed in your home is appropriate if your heating and air conditioning contractor never had the correct specifications for the project? The obvious the answer is that you can’t. If your HVAC contractors aren’t asking questions like this on each project they provide a quote for, it’s very possible that they are simply guessing what their job material and labor costs MAY be based on a system size that was determined by using an old school rule of thumb.

It’s easy to tell… just divide the number of tons your HVAC contractor quoted by the total conditioned square feet. Many times you’ll find that the total tons per square feet are 600, 500 and in some extreme cases, 400 SQUARE FEET PER TON! If you aren’t building glass houses, then you can rest assured that 400 square feet per ton will give you a system that is grossly over-sized. In fact, you’d be hard pressed to find a house built to today’s building codes that require less than 750-800 square feet per ton.

The fact is that in my almost 30 years of working in the residential HVAC industry, I don’t recall ever determining that the reason a heating or air conditioning system wasn’t properly heating or cooling a house was because the system was too small. Your HVAC contractor knows that if they install a system that is too small, it will be an extremely expensive venture to replace the system (including the duct system) after the house has already been built. This is one of the reasons why rules of thumb overestimate the system size that is required.

If the systems that are being installed in your homes are larger than they should be and/or the duct system that they are connected to is incorrectly sized, consider it a certainty that your homeowners’ monthly utility bills are going to be higher than they should be, not just for the life of their HVAC system, but for the life of their homes.

Here is a simple way to think about how an over-sized system can result in higher monthly utility bills. Think about the air conditioning system’s operating efficiency the same way that you think about a car’s miles per gallon (MPG).

Your car may get 35 MPG on the highway but when you are driving in the city, it may only get 28 MPG. The reason for this is because when you are driving in the city, your car is constantly stopping, then accelerating and then stopping again. It takes a lot more gas for your car to accelerate than it does for it to maintain a set speed.

Your HVAC system is very similar but instead of measuring its operating efficiency in MPG, it is measured in SEER or AFUE ratings. Since HVAC systems only come with a “city miles per gallon” rating, it’s easy to assume that your system must be operating at that advertised efficiency. The fact is that an oversized HVAC system may never operate at the advertised efficiency because it may never finish accelerating before the temperature in the space has been reached and the system cycles back off.

It typically takes 12 to 15 minutes for an HVAC system to get up to its optimal operating gas pressures (aka steady state). During this 1st 12 to 15 minutes, your air conditioning system is operating at an extremely low overall efficiency. If your HVAC system typically cycles back off in 15 minutes or less, that 15 SEER system that was installed may never operate at efficiency higher than 10 SEER.

The fact is that 9 times out of 10 (actually more), when a home builder places an order for an HVAC design by ConsultAir, they save more money on the HVAC system installation than the amount they paid to ConsultAir to have the system designed.

Here is a typical example:

• You (Builder) are building a 3000 square foot home. You already have a quote from your HVAC contractor to install a 5 tons air conditioning with a 100k BTU gas furnace. The quoted price is $8000.
• ConsultAir’s design calls for a 3.5 ton air conditioning system with a 60k BTU gas furnace. You request a new quote from your HVAC contractor and your revised price is $6000 or a savings of $2000.

After deducting ConsultAir’s design cost (about $500), you just saved $1500 and improved the overall quality and efficiency of your home at the same time. Keep in mind that I haven’t included the added savings that are realized by having fewer comfort related warranty calls.

Value engineering at its best!

If an HVAC Contractor has the benefit of a quality and proven design, the likelihood of incurring additional costs not captured in the original material, equipment and/or labor estimate are substantially reduced.

Utilizing one proven design will substantially reduce the number of HVAC related warranty inconveniences for your customer as well as reduce warranty costs for the Builder and HVAC Trade Partner.

As you know, the full potential of many of the energy efficiency features that you build into your homes can only be achieved when combined with a professionally and properly designed HVAC system.

By utilizing a Builder Provided HVAC Design, you will be giving your sales team an opportunity to not only educate your prospective home buyers about how your unique approach to the design of your HVAC systems will benefit them, but when presented properly, your prospective homebuyers will then be armed with a great topic for discussion as they continue their search for their new home by visiting with the sales teams of other builders in your area.

A comprehensive Builder Provided HVAC Design should consist of:

• Room-By-Room Manual J Load Calculation
• Manual D Duct Design
• Manual S Equipment Size Selection
• 11×17 Mechanical Drawings (to scale)
• Detailed HVAC Scope of Work and Specifications
• Option Details and Design
• Standardized RFP Response Form for the HVAC Contractor to enter the base house and itemized option prices

A Builder Provided HVAC Design is a true “Win/Win/Win” for the Builder, HVAC Trade Partner and the future Home Owner