Understanding SEER Rating

In the middle of the real estate boom, the United States Department of Energy mandated making the minimum SEER rating of our HVAC systems 13 SEER or greater . This would go in to effect in January of 2006, and many builders and HVAC companies were warehousing older 10 SEER units for cheaper installations and parts. I was a real estate agent at this time and the decision was not popular with many of my colleagues. “It’s just going to make homes more expensive” and “my old unit works just fine, why does the government have to get involved” were the most common complaints. We didn’t like it, but honestly I don’t think any of us could have explained what a SEER rating even meant!

SEER stands for Seasonal Energy Efficiency Rating and is an average of the unit’s cooling efficiency. Simply stated, the higher the SEER, the more the efficient the unit. As a mathematical formula it would read:

Total cooling output over the cooling season / total energy input over the cooling season

Luckily many of the older lower SEER units installed before 2006 are long gone. The average lifespan of an AC unit is 10-15 years, but it is possible that if you are still running one of the old ones it could have a SEER rating of about 6. It is not uncommon today to find units operating at a SEER as high as 27 and while the upfront cost is higher, you will pay less over the course of its lifetime.

Below is a comparison of the cost of operating a 6 SEER unit compared to a 13 SEER unit. Both are 3 ton units (36,000 BTU) running 8 hours per day. We’ll say that the cooling season is 4 months long and the average utility rate is .10 cents per kilowatt hour.

6 SEER

36,000 BTU/hr. x 976 hours / 6.0 SEER = 5,856,000 watts / 1,000 (to convert to KW) = 5,856 KW x $0.10 = $585.60 per year

13 SEER

36,000 BTU/hr. x 976 hours / 13.0 SEER = 2,702,769 watts / 1,000 (to convert to KW) = 2,703 KW x $0.10 = $270.30 per year

This is an annual savings of $315.00 per year, or $4725.00 over its average 15 year life span. Rebates from your local power companies will often bring the cost of the higher SEER units more in line with the minimum SEER models, so be sure to check before purchasing.

Even if you are not ready to replace your older unit, you might want to consider having your duct system tested. 20-40 percent duct leakage is not uncommon and a homeowner repair is not difficult. Doing this now will ensure that you are milking every last ounce of cool air from your existing system. It is likely you will begin to save money without replacing your existing system! 

Homework 2: Duct Sealing

                                        Homework 2: Duct sealing

Since we breezed right through the air sealing mentioned in the previous blog, let’s move on to duct sealing. One of the things that I neglected to mention in the previous post was that some of the processes I am describing for saving energy in your home are based on living in central Georgia. Climates with different humidity levels would certainly be handled somewhat differently, but for duct sealing it’s all one in the same. The more conditioned air you keep in your home and duct system the less your unit will run and the cost to heat and cool will go down.

If you’re anything like me the understanding of how exactly a heat pump air conditions your home is a big mystery. You turn it on, a miracle happens, and cool air comes out of the registers! Really I understand a little more than that, but for duct sealing you don’t need to understand how the magic happens, you simply need the will and a few materials.  A bucket of mastic, 24”zip ties (two for each connection), a razor knife, foil tape (not duct tape!), a bottle of rubbing alcohol and a box of disposable latex gloves. All of which can be purchased for less than $100 at Lowes or Home Depot, but I prefer my local hardware store.

I would be glad to go in great detail about how to seal each and every connection, but really you just remove each connection, clean with alcohol and coat with mastic. If you liked making mud pies as a kid you will have no problem duct sealing. There are some great videos on Youtube.com and wxtvonline.org that will lead you through the process step by step and it is a homeowner friendly job. By sealing your system you will prevent air leakage in to (and out of) your home even when the system is not running.

What you need to think about when doing this job is that the air moving through your duct system is inside the envelope of your home. When you have leaks you are mixing outside (unconditioned) air with the expensive air you have conditioned. When your duct system is in the crawl space you are mixing in damp, potentially moldy air. When it’s in the attic you are mixing in insulation particles and very hot air. And don’t for a minute think this applies only to older homes and systems. 10%-35% leakage in systems that were new or only a few years old is not uncommon; I’ve seen them first hand. To sum it up-If you don’t have mastic on all duct connections you are giving money away! Time to play in the mud!