When it comes to load calculations, guessing isn’t good enough

Would you put monster truck tires on the family station wagon? What about a 300-watt bulb in a 60-watt lamp? Common sense tells you these are bad ideas, but a harder-to-spot size mismatch could be happening in the homes of co-op members.

Fortunately, there’s a handy way to catch it—by performing a load calculation. To understand why, we spoke to Fred Clade. Fred is an HVAC trainer at the Indiana Community Action Association (INCAA), which provides training and technical support to the Indiana Weatherization Assistance Program.

Fred is also a Building Performance Institute Professional, and he holds the EPA Section 608 Universal certification, the North American Technical Excellence certification in gas furnace, heat pump, and air conditioning, and is an Esco Institute Section 608 and North American Technical Excellence certification proctor.

In other words? Fred knows the business, inside and out.

So just what is a load calculation, anyway?
It’s a way to tell how much heat the house gains or loses through doors, windows, the roof, and so on. The load calculation tells us how much we need to put back in, whether it’s in the form of heating or cooling. When we go to put in an HVAC unit, the load calculation is a critical part of the process.

Is a load calculation necessary? Can’t the numbers just be estimated?
If you guess wrong, it costs the homeowner money. You’re hurting your customer. So it’s critical to get the right numbers, because you don’t know what the house needs until you’ve done the actual calculation. With an oversized unit, it’s going to take longer for it to reach a state of efficiency, and during that time the homeowner is wasting money and energy because you were cutting corners you shouldn’t have.

I like to compare it to driving a car. Let’s say we start out from the same place, and I go 30 miles an hour the whole way while you go from zero to 55, back to zero, back to 55—which of us is going to use more gas? The same principle is true of your HVAC unit. The back and forth that happens with an oversized unit is going to run up the energy bills of co-op members.

That’s a concern for any HVAC contractor who cares about doing right by the customer, and it ought to be the first thing that’s done on every house. Otherwise, you’re responsible for the wasted money because you chose not to perform the load calculation and size the HVAC unit right.

That would wear out my car faster, too. Is the same true for an HVAC unit?
It is. When the HVAC unit is oversized, it cycles more often and really lowers the life of the equipment. I used to process warranties as a tech rep for a distributor, and you always saw the same parts failing on equipment that was oversized.

Sounds pretty important, then, if you’re building a new home.
It’s very important, and on new construction the Department of Energy requirements mean it gets enforced more often. It’s a state building code requirement, and load calculations are also required for the Indiana Weatherization Assistance Program, so we see it done more regularly when a new home is being built.

Unfortunately, it can sometimes get overlooked on replacement work, because there’s a temptation to rely on looking at what the last guy installed. But a good contractor will never rely on what the last guy did.

Why is that?
The fact of the matter is you don’t know if it’s right. Maybe the last guy didn’t do a load calculation, either, or maybe he got the sizing wrong. Even if you’re putting in the same heat pump as what was in there before, if it got sized wrong then you’re only continuing the problem. If the homeowner has been losing money, they’ll just keep losing money. Performing a load calculation is the only way to be sure you’ve got the right unit in the home, and without it you can’t honestly say that you’re doing the job you’ve been hired to do.

Since members see so many benefits from energy efficiency, is there anything they can do to make sure a load calculation is performed?
Co-op members should request a copy of their load calculation. And remember, a load calculation is required in order for members to receive a POWER MOVES rebate on residential HVAC equipment. So it’s not just a matter of saving money and energy in the long run—they’ll see immediate benefits through the rebate program itself.

Okay, I see how it benefits the homeowner, but doesn’t the load calculation cost trade allies a lot of time and money?
Most contractors actually use a computerized load program now—you just plug in the numbers, and it tells you what size to put in. The first time you do it, it can seem like a big deal, because if you’re unfamiliar with the process it can take a while. I understand that, and I do understand why contractors want to avoid it. But it is not a difficult process, and once you learn, it goes much faster. It just takes practice, and with a little experience it’s not a difficult process.

Co-op members don’t always realize when they’re losing efficiency due to an oversized HVAC unit, so it’s important that the contractors get it right. And a good contractor will use this as a selling point. They can say they’re saving homeowners money by qualifying them for the POWER MOVES rebate, so the unit costs less to purchase, and they’re saving homeowners money by making sure they don’t waste time and energy over the life of the unit itself.

And the best part for trade allies is that if they take the time to explain it to homeowners, that person becomes a customer for life. That’s loyalty, and free word-of-mouth advertising, all for taking the time to do the job right in the first place. I think that’s well worth the effort.