New Air Conditioner

When I moved into my house 16 years ago, the furnace was already old, but it worked. The air conditioner was not as old, but it worked too. I had a Georgia Power energy consultant come by back then who said the air conditioner wasn’t that bad. It’s not a name brand of any kind, and I have had to call the repair man a couple of times, but for the most part the system has been pretty reliable. I’m not sure how efficient, but the bottom line is I don’t spend a huge amount on heating and cooling throughout the year, maybe $500 based on the increased usage of power and gas during the summer and winter respectively. So if it wastes energy, it isn’t costing me much.

But when I replaced my refrigerator and started saving a significant chunk of electricity every month, I started thinking I could do better. And that’s true to some extent except that the air conditioner only runs hard for about three months whereas the refrigerator runs all year long. Plus the refrigerator was pretty cheap compared to central air conditioning system.

The other thing is that there are federal tax credits for making your home more efficient, and Georgia Power offers rebates for improvements as well. When I replaced the windows in my house I found that additional cost for meeting the federal tax credits was way more than the tax credit itself and the differences in performance were pretty minor. So for windows I didn’t even try to get the credits, even though the new double pane windows were a big improvement over the original single pane ones.

When a guy came around doing energy assessments recently, I thought this might be the push I needed to go ahead and upgrade the system I have. He determined that the ducts are pretty leaky and the returns aren’t insulated. Even the supply lines which are insulated probably don’t have as much insulation as they should. He could fix them or replace them.

I am replacing both the air conditioner and furnace, but first the air conditioner:

Efficiency The efficiency of an air conditioner is measured in SEER and you qualify for a $300 federal tax credit if you install a 16 SEER system (also has to meet an EER rating of 13, which seems to be harder to achieve; Wikipedia says EER is a better measure in humid locations, but all you ever hear about is SEER). Some of the people who have given me estimates guess that my current air conditioner is 9 SEER, so a 16 SEER system would be 78% more efficient. All new systems have to be at least 13 SEER.

Capacity The capacity of an air conditioner is measured in tons and sometimes BTU. 1 ton is 12,000 BTU. By knowing the square footage of the house and the local weather and whether the house is one story or two, they can figure out how much cooling capacity I need, but they don’t have to get incredibly close because air conditioners are made in half-ton increments. I need a 3-ton unit. The idea is you don’t want too much capacity because otherwise the system just blows a blast of freezing cold air for 10 seconds at a time. The AC will be more efficient if it runs longer since that gives more time to get all of the air out of the ducts.

Stages A 2-stage condenser can run at high or low. There are some systems that include two condensers, a little one and a small one. The little one can run when not much cooling is needed, or the big one when more cooling is needed, or both when it gets really crazy. I don’t think the ones I’m looking at have multiple condensers, but the more expensive ones have two stages, which is supposed to be better. However the two-stage one I’m looking at doesn’t qualify for a federal tax credit because the EER value is 12.5 instead of 13, even though the SEER value is 16.2. The sales guy said the EER value isn’t as good because the federal criteria only includes running the AC at full blast and there are times when running on the lower setting is more efficient. I’m not sure they’re more efficient on low, but the sales guy said the system low runs at 70%, but if you measure how many amps are being used, it is more like half.

Furnace The efficiency of a furnace is measured by AFUE which is the percent of heat in the burner that actually goes into the house instead of up the chimney. The chimney is where my furnace exhaust runs right now, but this isn’t allowed for chimneys lined with clay tile (pretty much most chimneys) because the moisture can degrade the tile and maybe eventually allow exhaust into the house (when natural gas burns it produces water and carbon dioxide, so there is always moisture in the exhaust). They could run a pipe down the chimney, but the other choice is I can go with a high efficiency furnace of 95% AFUE. The exhaust from a furnace like that has had so much heat removed from it that it isn’t even all that hot anymore and can run through a PVC pipe out the side of the house. They run it up a slight incline and any moisture that condenses in the pipe runs back to the furnace where it is dumped into the house’s drainage line. To make it so that you only need one opening, they run the supply line inside of the exhaust pipe. This is better than the current system which draws air from in the crawlspace itself which will then just be replaced by cold air from outside. The good thing is that any 95% AFUE furnace qualifies for a $150 federal tax credit. They think my current furnace is 60-70% efficient. You aren’t even allowed to buy a furnace that is less than 80% efficient.

They have stages with the furnace as well, so they can run on lower heat. But confusingly they also have 2-stage heat exchangers where they just run the exhaust gas through a second heat exchanger to extract more heat. Like the stages with cooling, having a 2-stage furnace is more about comfort than about efficiency.

The other big option for furnaces is whether you have a constant speed fan or a variable speed one. Variable speed is better and more efficient, usually qualifying for a $50 federal tax credit, but also bumps the price up. When that fan is combined with an air conditioner it can also help control humidity. Another thing it can do is run at low speed, keeping the temperature in the house more even, and filtering the air even while it isn’t heating or cooling the air. This is more for comfort than efficiency.

There is also something about the coils, but nobody has talked about that much so far.

Filter It seems like everyone is pushing these giant air filters now. While an old-fashioned filter is 1″ thick, these are 4″ to 6″ thick. There are also electrostatic filters. And they aren’t cheap either, some of the filter media cabinets adding thousands of dollars to the price tag. While I can get a 1″ filter for a couple of dollars, the 4″ filters are more like $30. They last a little longer, so while the HVAC guys say you should change a 1″ filter every month (seems excessive), you should change a 4″ filter every 6 months. The cabinet has to be built to accommodate the right size filter, so this is a decision that has to be made up front. You can get 1″ pleated filters (one guy said don’t get the old fiberglass ones because they don’t stop anything), but I went ahead and allowed them to put a 4″ filter box in the system. $30 times 2 filters per year times 10 years is $600, which maybe isn’t that bad for clean air. Plus you don’t want a bunch of dust and dog hair messing up a system which costs $5,000 to $8,000.

Thermostat The last component is the thermostat. All systems have programmable thermostats now, but the higher end ones have a color touch screen like a 7-inch iPad and even come with wi-fi that will give you the weather forecast and let you control the system via your home wi-fi network and an app that can be run from anywhere with internet access. One has a SD card slot that lets you turn the thermostat into digital picture frame that will run a slide show of pictures on the card. There was a one-touch vacation feature where you could just press a button and the temperature would automatically hold at 85 degrees (for air) or 55 degrees (for the furnace) until you pressed it again. They showed a short video where some people went on vacation and set their heat back, but their flight was cancelled and they were able to turn the heat back on from the airport instead of going home to a cold house (I think that’s what happened anyway). Also the thermostat is smart enough that if you say you want the house to be 70 degrees at 5 o’clock, it will come on a little early so that the house will be 70 degrees by the time you asked for it. Otherwise you might be stuck having to enter 4:55 as the time to give the furnace time to heat up. So I’m not sure what advantage the fancy thermostats have, but they definitely do more than old thermostats that were either on or off at a specified temperature since they are controlling variable fan speeds, variable burners, and 2-stage air conditioning, as well as humidity in some cases which they can manipulate by changing the air speed and cooling power. The good thing is that Georgia Power has a 50% rebate up to $100 on any programmable thermostat and I think all of these will get me the maximum. Even though I already have a programmable thermostat, it is old enough that replacing it still qualifies for a rebate (has to be 10 years old and mine is 11). The other nice thing is the programmable thermostat rebate is in addition to the overall energy savings rebate that is also available.

Heat Pump Since I am getting a new air conditioner, upgrading to a heat pump usually isn’t that much more expensive. I love the idea that by moving heat instead of generating heat, a heat pump can actually add more heat to the house than the energy it is using. It does this so well that one system I was looking at was 350% efficient. Grant says he always installs heat pumps in his houses, but he isn’t installing gas lines either. That’s not a bad way to go. My gas bill is $26 per month even if I don’t use any gas at all, and that amounts to about half of what I pay yearly. So even if the heat pump wasn’t as efficient as gas, I think I could save money if I could completely eliminate gas. However, all of the installers recommended against a heat pump, saying that with a 95% efficient gas furnace, a heat pump can’t compete. I found a spreadsheet that calculates heating cost of systems and found that gas would have to go up to about $1.35 per therm before it would be more expensive than a heat pump running on electricity at 14 cents per kilowatt-hour, though it also depends on temperature since the coefficient of performance of the heat pump drops with the temperature. With the smart thermostat you can set gas heat to take over at a certain outside temperature or, this is neat, you can enter the cost of natural gas and the cost of electricity and it will calculate whichever one is cheaper. You have to keep the prices up-to-date yourself (for now, though with wi-fi maybe it could look it up) and at current rates I imagine the switchover to gas would happen at fairly high temperature. One neat wrinkle to the heat pump equation is that one system I was looking at would cost $700 more if you installed a heat pump. However the system without the heat pump just missed qualifying for the federal $300 rebate for efficient air conditioners. But as a heat pump it did qualify. So now the heat pump would only cost $400 more. It may not cost much for the heat pump upgrade, but Consumer Reports reports that repair rates for good brands goes from about 12% for a/c only to 19% for a/c with a heat pump. It kind of makes sense because you are running that compressor way more often than before, so it will probably break down more often. If a compressor will last 15 years, as a heat pump it might only last 8.

Brand Names Consumer Reports ranks American Standard, Bryant, Trane, and Carrier as the most reliable brands, but Lennox and some others are very close. Then there is a third tier including Goodman, Amana, and York. Trane and American Standard are the same. Also Bryant and Carrier are the same. Amana and Goodman are also the same. Lennox doesn’t seem to share, but they seem to have similar thermostats, which are usually made by Honeywell. Grant says his HVAC guy usually installs Bryant heat pumps. I found out that Jeb just recently replaced his two systems with Carrier and has been pretty happy.

I checked the local bulletin board to see which installers people liked because the installation is really more important than the brand. I then cross-checked some of those installers on Yelp and Kudzu, but those reviews weren’t that helpful, so I subscribed to Angie’s List for a year for about $18. Angie’s List has better reviews, but I learned they are generally all pretty positive. I do think I wound up getting estimates from three pretty good companies, two of which install Lennox and one that installs Trane. I didn’t realize Jeb had recently gone through this or I would have gotten an estimate on a Carrier system instead of two on Lennox. I also read a lot on Gardenweb forums and some on an HVAC forum. I couldn’t find any Carrier or Bryant installers that I felt comfortable with, though I’m sure they are out there.

All of the guys that came out had many years of experience and seemed pretty knowledgeable. They probably felt like they could do pretty good work and were wary of companies that would low ball a system. One test the first guy said I should use was whether they figured out the thing about not being able to run exhaust up the chimney, and all three knew that. It’s a real process getting the estimate and going over the options so I spent an hour or two with each of the three. None of them did a load calculation, but they all came up with 3-ton systems. And the prices were pretty close on comparable systems, though they definitely push you towards the higher priced systems. Even so, they weren’t recommending their very highest end super-efficient models.