This week we have Jason Wall who has spent more than 23 years working as an HVAC technician with Griffith Heating and Air. He specializes in working in older and historic properties which includes his own 1920’s Pennsylvania house. In a recent piece for Home Energy Magazine Jason said “At one point not too long ago, it felt like the HVAC contractor community was strictly against the home performance community. One wanted to improve our home’s energy efficiency without sacrificing our climate control needs—and the other? They wanted to sell expensive metal boxes and scramble for the door before clients saw their energy bills come in.” For more on one of the issues that leads many to agree with him, let me turn it over to Jason…
The Oversight of Oversizing: Why Bigger is Not Always Better With Air Conditioning
For technicians and professional servicemen, it’s one of the oldest tricks in the book. Selling oversized and overpowered equipment to turn a bigger profit has been a practice among a disreputable minority of providers since the dawn of modern appliances. This is especially true when it comes to air conditioners, and advertisers know how to hit hard in the blistering heat of Summer in order to persuade clients that a bigger system holds all the answers to their indoor climate control problems.
This isn’t true all of the time – I’ve known plenty of friendly servicemen who have only the best intentions for their clientele. Sometimes, technicians will falsely bill a larger system as the solution to problems such as warm spots in an environment. Occasionally, technicians with good intentions over-ton a house because they don’t realize how much more efficient today’s air conditioning is compared to its ancestors. And of course, many hawk bigger units simply because they want to turn a bigger profit.
While this isn’t necessarily a rampant problem, it is always wise for consumers to do their homework on what an appropriately sized unit would look like for their property rather than solely relying on the word of a lone technician to purchase an oversized unit. In fact, under-sizing a unit is significantly preferable than oversizing one.
HTRC: But wait, how can this be true? Well the fact of the matter is that a properly sized unit is designed to handle all but the most extreme weather which may only occur for a few hours each year. While it is called the 1% factor / outdoor design condition does not equate to 87.6 hours but in many cases 0 to 13 hours in almost any given year. Does this mean that the temperatures inside will skyrocket or plummet? No, it just means that the unit will be running non-stop (which is actually the most efficient) & the temperature inside may start to climb very slowly but will return to normal in just a few hours if it truly is spec’d that close (which is rare).
For example I recall I was walking in Phoenix when it hit its record 124° which grounded all planes taking off as their charts only went to a 122° at the time. Well within a few hours it had cooled down enough so that the planes could resume talking off & yes, they updated those charts in case it ever happened again. Yes it has been a while…
Consider this: A system which is too powerful for its environment will reach your desired temperature quicker, meaning it cycles more often. This results?
- worse energy efficiency − higher energy bills every month
- worse abilities to dehumidify – unable to achieve balanced humidity, meaning an uncomfortable environment and potential moisture damage in your property
- a greater likelihood of mechanical failure − you’ll have to replace it sooner than you would with an appropriately sized or undersized model
No matter which way you slice it, oversizing is the expensive mistake that keeps on giving. In order to accurately size a system and avoid these various complications, follow these steps:
HTRC: In all seriousness I do not recommend the following steps for properly sizing one but they can be used as he put it as “I’m also aware that the method I laid out isn’t exactly ideal, but I was hoping to provide some actionable advice in my work that the DIY average Joe can use.” With so many reputable firms now offering Manual J & D’s on the internet and many being required to by code for installations…
With that, if you run these numbers & your HVAC technician is quoting higher, I would definitely have them “show you the numbers.” In many cases most go by the old stand by of 500 SF per ton, while most that are built to code are averaging around 800 SF+ with many higher energy efficient ones in the 1500 SF per ton range. (1 ton = 12000 BTU of cooling / heating & 400 CF of air)
- Determine how much square feet needs to be covered. To do this yourself, simply multiply the length of a location by its width for rectangular rooms. In triangular spaces, multiply the length of an area by its width and halve the number.
- Figure out how many BTUs (or British thermal units) you require for each area. This can range drastically depending on your area, and taking care to neither surpass nor fall short of this number can make a big difference to your energy efficiency in the long run. For a handy chart, reference Energy Star’s guide.
- Adjust each room according to your area’s conditions. Areas with high traffic on a regular basis should reflect an additional 600 BTUs for every additional person on the area’s average occupancy. Most notably, kitchens should accommodate an extra 4,000 BTUs. Areas which are particularly sunny, particularly those with heavy exposure towards the equator, require a boost of ten percent to your capacity. Conversely, rooms which are mostly shaded are fine with ten percent less than normal.
While taking the time to measure and tally up the right number of BTUs your air conditioner will require in order to run efficiently can be laborious and difficult, it is an important project that will impact your energy costs for years to come.
However, to recognize your heating and cooling needs with the greatest specificity, there is no substitute for the manual J and D calculation sizing method. Determining how many BTUs you require through the method listed above can provide a ballpark estimate, but it does not take ductwork, climate, entry sizes, ceiling height, insulation, and several other factors into consideration. This computerized method is only available through licensed professionals, so seek out such a service if you want the greatest precision before committing to a new unit.
Always do your homework when considering purchasing new equipment. And if you’re experiencing troubles with your air conditioner, it wouldn’t hurt to see if your system is correctly sized for your needs.
Once again I would like to thank Jason for this piece and his thoughts. While he might not be in the field as much as he might like anymore the bright side is he gets to help others learn more about the HVAC trades, enjoying spending more time with his kids, and of course watching a little more baseball.