Why HVAC Isn’t Just a Lot of Hot Air (or Cold, Either)

Ever since I started my career in the construction industry, I have always seemed to run into problems with HVAC systems. This shouldn’t be that surprising, since the HVAC system is the primary system responsible for the living conditions in your home and can have the most impact on how a building functions. I have seen systems that are contaminated with fungal growth, systems that you would think had been installed to provide irrigation to the crawlspace, systems that my 8 -year-old niece and nephew could have installed, and systems that are a piece of art. However, out of all of these, the latter is the rarest of them all.

In the past year, I have dealt with systems that

  • increased the gas bill after the system was installed,
  • caused the homeowner to pay more per month than they were per season before it was installed,
  • were not cooling or heating the home equally. The excuse for this was that two systems should have been installed, when the contractor installed only one – however, that one unit was not properly installed (twice), and ended up causing damage to the ductwork.

These are only three of the multitude of cases where I have seen of improperly sized, installed, or designed units. Why is this? The only explanation I can come up with is that homeowners – and unfortunately, most HVAC technicians – do not understand the impact the system can have on the home, and that it is not as simple as a fan moving air through some round tubes.

There is a standard of practice set forth in both the building code and by industry organizations that state how a system should be designed. This process takes into account how each component of the system works with the other, and combines them to provide efficient delivery of your conditioned air. This whole process starts with what is called a load calculation, or Manual J calculation. This takes into account the construction of your home and how heat is transferred between the exterior walls, ceiling, floor and the exterior environment. The next step covers the system selection or Manual S. This outlines the proper method to select a system to accommodate for the required load calculations. Next comes Manual D, which is another critical step as this is the duct design. Each system must have the ducts designed for the unit to be installed. Finally is Manual T, which is the register and grill sizing. Even grill sizes can impact your comfort levels!

Properly designed systems can increase your comfort and decrease the cost of your utilities. Next time you are going to have your HVAC system replaced, take note of these simple reminders, and hopefully, you will have your system properly installed:

1. Make sure Manual J, S, T, and D calculations were performed for your system.
Of all of these, Manual J and D are the most critical. Whether you are having your home system replaced (ducts and system) or just the unit, these calculations are critical. There is no such thing as rules of thumb or matching the system with what you previously had. Each home is unique, and the system you had before may have been improperly sized.

2. Your ducts impact your system’s efficiency.
While most people will try to just install a new unit and keep using the old duct work, this can actually cost you money. If ducts are improperly sized for the system, they can cause the system to operate inefficiently. Why pay for the more efficient system if it is going to operate at a lower efficiency than the one you just replaced?

3. Manual J has safety factors already figured in.
There are some companies that will perform Manual J calculations, but they will not use the weather data provided in the back. Instead, they will design the system for hotter temperatures. You don’t design systems for newsworthy days! By raising the design temperature, you oversize the system. When you do this, you size the system for 1% of time it is in operation – and oversizing for 99% of the time.

4. The lowest or highest price may not be the best.
It’s hard to judge an install on just the price of the system. HVAC installs can vary greatly! ACCA (Air Conditioning Contractors of America) has produced a document that allows you to compare bids so that you get the best value. However, remember that if the contractor doesn’t properly design the system, it doesn’t matter how good their price is! You can get the document here: Quality Installation Specifications


Do NOT Install Replacement Windows!

The tip this week is more of a what not to do instead of a what to do. Every day, I see a commercial advertising replacement windows and how much money they can save you; and every day, I know someone has invested a lot of money into their home that they will not get paid back.

Many people are advertising 50% savings with the replacement of new windows. This is completely true. You may save 50% on the amount of energy the windows cost you, but this translates to only about 10% to 15% of your total bill. With this limited savings as compared to the cost of the windows, you end up with a very long payback period. If 10 windows cost you between $6000 and $7000 and you save a gratuitous 20% on a utility bill of $200, your payback will be between 12 and 15 years. This is almost a best-case scenario. In most cases, the paybacks for replacement windows are going to be between 20 and 30 years, because the savings will not be that great for such a small investment.

Most homeowners are not going to be in the home for 15 years, and if they are, there are several other items that can be done to the home that have a quicker payback. I will only recommend replacement windows in extreme cases. In the majority of the homes I see, I would more likely recommend installation of storm windows (for single panes), or repair of the windows currently in place, typically because those are the best scenarios when windows are involved. So next time you have someone suggest you replace your windows or you see the commercials, remember that those windows will save you money, you are better off investing in other, similarly effective improvements that have a much shorter payback period.

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