New HVAC & Home Energy Audit

xtremeski2001

9 years ago

last modified: 9 years ago

Hi All,

Got great advice here for my new HVAC and it was installed a few months ago. We went with all Carrier equipment (AC - 4-ton two-stage 24ACB748 w/ NIM Control 16 SEER, Furnance 59MN7A100VZ1 97.3% AFUE, and AA600M humidified). We live in SE Pennsylvania and have a 2,650sqft (3,500sqft if you include basement) two-story home (w/ unfinished daylight basement). Our heat is natural gas, AC is electric, home built in 1992.

Our heating bill went down ~20%, less than I expected. However, after our new equipment was installed we had a home energy audit performed (hooked the fan up to our door, created negative pressure, covered the vents, used a infiltrometer, etc.) and wasn't sure what level of reliance we should place on it and whether any of their suggestions would result in a "material" difference (either via the bill or in comfort). Would love to read your thoughts!

It's hard to summarize all the data, but is says total leakage area is 3.3sqft, and air exchange rate is 10.72 times per day. There appears to be the most leakage via the returns (which use the wall cavities). The summary says we lost about 1.90 tons of AC (48%) on the hottest days and 29,244 BTUs (32%) on the coldest days. They calculate this as 36% loss in SEER and 24% loss in AFUE. In otherwords, our brand new 16 SEER AC is operating at a 10 SEER. Our 97% AFUE furnance is operating at 61%. It's no wonder our bills haven't gone done!

They recommend the following:

1 - Bring attic insulation to R-38 (from R-18).

2 - Seal duct work

3 - Aeroseal duct work

4 - whole house dehumidifier (I think our AC does this already)

5 - A lot of small fixes ... replace weather stripping, caulk cracks, etc.

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Comments (10)

mike_home
9 years ago
You have some very good equipment. I am not sure you needed a 100K BTU furnace. Was a load calculation done?

A reduction of 20% heating is very good. Some of that reduction is due to falling gas prices.

All energy savings are good. The question is do they all make sense financially. You should definitely increase the attic insulation if it is fact only R-18. This is something you can do yourself. Sealing the duct work is important especially if it is in non-conditioned space. You should not need a dehumidifier with a 2-stage AC. If you do then something is not right with the installation.
udarrell
9 years ago
last modified: 9 years ago
where do you live?

need to know the winter & summer design temps.

appears that everything may be way oversized; that is why the load-calc & retrofit is performed before buying equipment.

you cannot accurately compare energy costs between old & new as weather conditions & other factors affect energy usage.

your experience illustrates the importance of doing everything right & in the proper sequence.
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Yes, the mastic stuff is the bomb! I had used it on a chlorine leak scrubber system some years ago. The trick is to buy or mix to just the right consistency and then you are basically painting a plastic seal or your chosen thickness. I too think the aluminum duct tap is expensive, but it is approved, gives a good smooth interior, and when used over the mastic I will bet it stays in place giving the best of both. We used IR to check our electrical connections in the plant. 480 volts at 100 amps generates measurable heat when the connecting screws are loose and that uses power. So, though I have not had the energy audit I have purchased an IR gun (got it cheap!) and am finding lots of unexpected holes. I was also surprised to find the walls did not show the heat level I expected. It turns out that the previous owner did some exterior wall insulation. A 1950's house here in California had next to none. This means that my AC unit is oversized, not having that loss to compensate for. It will still work out. I will have to fine tune for efficiency now, but if I ever build the extra conditioned floor and attic space it will be about right. The furnace is still oversized, but that is why I went for the two stage. It just hit me that what most of you guys are talking hard duct as it is normal. That stuff is better done by a professional unless you have all the equipment and can afford to practice (waste cost). But then you would, if you did your research, nearly a professional. I am doing Flexible ducting now because it's easy and my final configuration will not be fixed. My attic space and roof may be changing in the future if I can find the money. At that time I will be doing hard duct, wall stacks, and the like. That is major and will probably be contracted. Right now I want to spend as little as possible to get my system working. I have a wall heater and window air, so the efficiency increase could be as large as 50%. Just replacing my water heater with a tank-less last December gave me about a 15% reduction in gas usage and I think we are using more because it doesn't run out in the shower anymore. If the HVAC works as well I may save over $100 per month this summer on AC and an unknown amount next winter on heat. Hey, I just looked back at this and my other posts and realized that they are WAY long. I apologize. I am more used to writing memos, letters, and manuals. Give me time. I will get used to shorter posts.
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My first advice would be to find out how much insulation you currently have in the attic and what condition it is in. You should have at least R-30 of insulation. If you are adding more than it doesn't cost much more to increase it to R-40. I like fiberglass batts, but blown in insulation is fine as long as it is done properly. This is something you can do yourself or hire an insulation company. I am sure you were told that as part of the NJ Clean Energy Program you must seal your attic in order to qualify for any rebate. I have never seen any measured results of energy savings before and after sealing. The attic hatch should be sealed since in my opinion it is the biggest source of leakage. This is something you can do yourself. Several years ago I built my own insulated hatch for about $15. If you seen dirty insulation that is dirty in spots, then that is a source of a significant air leak. You can use silicone caulk to seal them, or you can have the insulation company seal and then insulate. I see that you have gotten some quotes. I also detect that some and possibly all have not done a load calculation for your house. Any HVAC contractor who quotes either a 2 or 3 ton AC for an 1100 sq. foot house in Middlesex County (I am in the same county) NJ obviously has not done a load calculation. If you are going to upgrade the attic insulation then do that first, and then get a contractor to do a real load calculation. If your windows are double paned and fairly tight, then I would think a 40K BTU furnace and a 2 ton furnace are the correct sizes. As far as equipment goes, I own Carrier Infinity equipment and so far I like it. The Bryant equipment is exactly the same. I am a fan of 2 stage furnaces and AC and in my opinion are worth the extra money. Trane/American Standard is also very good. I have no direct experience with Lennox, but from what I understand Lennox uses unique parts. The parts have to come from Lennox and are sometimes harder to get. I think you said your current furnace is 11 years old and 80% efficiency. Normally I would say to keep the furnace another 5-10 years. But if you plan to live in this house 10 or more years then you may want to consider replacing and keeping the correct matching AC. Here are my opinions on the quotes: Company #1 Quote #1: Carrier Performance AC is good, I don't think you need 2.5 tons and the price seems expensive. Quote #2 Carrier Infinity 58CVA furnace is very good, but it is only 80% AFUE. I recommend spending a little more money and installing a 95%+ AFUE furnace. The Infinity 24VNA9 is overkill for our climate. You can save money buy dropping down a model or two and getting an AC that has a SEER rating of about 16. If the AC is sized properly and is 2-staged then I highly doubt you need a whole house dehumidifier. That would be a waste of money in my opinion. Company #2 and #3 I am not an expert on Lennox, but I think some of these models don't compare that the Carrier Infinity in terms of features. The fact you are being quoted different AC sizes is a red flag for me. Company #4 Quote #1 Bryant Legacy 2.5 ton for $4600 seems reasonable. I would want to see a load calculation to see if you really need 2.5 tons. If you keep your current furnace you will have a mismatched system. It will work, but you don't know the SEER rating, Quote #2 Bryant Evolution is the same as Carrier Infinity. Very nice equipment but the price seems high. Here is quoting a 2 ton. So why is he quoting 2.5 ton in Quote #1? I see no size listed for the furnace. Quote #3 He now quotes the 3 ton size. I guess he thinks you may want to hang meat in your basement. A 3 ton AC, even if it were 2-stage, is going to short cycle and you will still have a humidity problem. Once you discover this he may suggest getting a whole house dehumidifier. Correct sizing is critical. This guy does not seem to care. In summary you haven't found a good contractor yet. Carrier rebates start March 1st. The March - April time frame is the best time to get quotes in our area. Contractors are not busy and the pricing is a little better.
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I'm disappointed that what had at first seemed a very balanced comment was followed by what seems to be misinformation and misdirection. People buy ground source heat pump equipment because they want to and can afford it. Or decide they need to in their locations. They're hugely more expensive than alternatives, which is why they're still not very common. "When’s the payback on a Tesla? People still choose to buy them for reasons other than the ‘bottom line’." Not a comparable. A false analogy. "I would not choose natural gas or propane for reasons relating to the environment, safety, IAQ & paying for yet another utility hookup for an energy source that might not even be used for months on end during the year." What effect having a gas furnace has on indoor air quality. Another hookup? Most people prefer gas cooking appliances and besides, the OP is talking about an existing home, he either has gas service or he doesn't. "Rather than spending perhaps tens of thousands of dollars on a Solar Array, I would sooner invest that same money, hopefully less, in a ground loop for a Geothermal system." Sure you would, that's the business you're in. The ground source heat pump market is not growing as expected by those in the industry, which suggests that your opinion isn't widely held or easily sellable. In many parts of the country, solar panels can have a quick payback. Not so ground source heat pumps. "I often hear about Solar Panels when geothermal is mentioned, as an alternative way to save money by creating energy." In a place like Texas, where electricity is cheap (other than during cold weather crises as they just experienced) there's likely no payback from a solar panel installation. People do it as a personal statement, call it for environmental or other personal reasons. Like buying the Tesla, not a financial decision. An HVAC system blows warm air when it's cold, cool air when it's hot. It's one of those things people don't care about - either it works or it doesn't work. Spending extra money for an exotic system doesn't equate to extra payback when the home is sold. Neither owners, nor visitors, nor people passing by, nor anyone else, concern themselves with what's doing the work. It's equipment that doesn't produce an experience for someone in the house if it's working. In the US, there are vast areas where electricity is cheap. It will remain so for some time. People don't spend money today to potentially save money 10 years out when market conditions may or may be different. I suspect you could build a house with mahogany or teak framing. Or you could paint the framing bright colors. Why bother, you can spend less money and effort and get something else that will do the same job. "We almost never use setbacks at our home - even when going on vacation for weeks on end with no one home, our geothermal just runs." You're combining two different things to produce confusion. Thermostats that have a setback feature ALL are set up to provide lower overnight temperatures to have more comfortable sleeping conditions and then a recovery in the morning before wakeup time. As sleep specialists recommend. That in demand comfort features isn't possible with ground source heat pumps because the warm up period from a setback is too slow to be convenient to use, absent triggering a secondary heating source (like a furnace) to help. THAT'S why you don't "believe" in setbacks with a heat pump - they don't work. Turning down a thermostat during heating season when the home will be unoccupied is not a "setback" as that word is most commonly used. It's done to save money, why heat a vacant house? No setback thermostat is needed, even a dumb 50 year old analog thermostat can be turned down.
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xtremeski2001
Original Author
9 years ago
Hi - Thanks for the responses.

- Mike_Home - They did a load calc and also estimated any additional BTU needed should we finish our basement (currently not heated). We had a 80 or 90k BTU before.

- Mike-Home - Sealing the ducts (especially those exposed in the basement) seems simple enough via mastic tape. However, the attic is blown insulation. I assume I would need to add more blown insulation, versus rolling out batts of insulation on top?

- Udarell - We are just outside Philly. Hot/humid summers and cold/dry winters.

- Udarell - They did the calcs and this is how they sized us. Our gas/electric company shows us a year-over-year comparison with average temperature and that's how I got to the 20% decrease.
mike_home
9 years ago
Your old 80K furnace was likely rated 78% AFUE, the new 100K BTU furnace is rated at 97% AFUE. The respective outputs are 62K and 97K BTU. I am skeptical your daylight basement has a heat load of 35K BTU. On a very cold day what is the the temperature of the basement?

The AC has a 2-stage condenser which only comes in whole ton sizes. A 3 ton condense is probably too small for a 2650 sq. foot house. I think you are OK with the 4 ton AC especially given the fact it is 2-stage.

If you have blown insulation then you would need to add more blown insulation on top. Adding batts on top of loos insulation is not going to work well.

The best stuff to use to seal ducts is mastic. It is applied with a brush, not a tape. Some aluminum foil tapes like Venturetape seem to work well.
xtremeski2001
Original Author
9 years ago
The old 80k furnance was ~60% AFUE. I recall the gentleman remarking about how old the unit was (based on 1980's technology) and must have been one of the last one's made considering the construction of our house in the early-90's. Either way, not much I can do about it now :-)

Yes - the installer explained the 2-stage and that's why we had to go 4-ton. He originally suggested a small unit, without two-stage, but I insisted.

I guess I could try blowing the attic myself, sounds more like a hassle than actually difficult. But between the attic and sealing the vents, these sound like the most bang for my buck repairs.
mike_home
9 years ago
If your furnace was operating at 60% efficiency then your savings would be 38%. The 20% savings you have seen so far would suggest the old furnace efficiency was closer to the 78% rating. Contractors are going to low ball the efficiency rating on anything the customer is considering replacing. It doesn't matter, you now have a better furnace that hopefully will last a long time.

I think the extra money for a 2-stage AC is worth the extra comfort of lower humidity. There is also a small savings if the lower humidity allows you to raise the temperature setting a few degrees.

I don't know how much insulators charge for blowing in additional insulation. Do it before it gets hot. It is no fun working in a hot attic.
fsq4cw
9 years ago
Your system looks good to me as long as you got the 'right' indoor evaporator coil.

Is there a reason beyond price for not getting an Infinity condenser or heat pump?

SR
xtremeski2001
Original Author
9 years ago
fsq4cw - I'm not sure I follow. I have a furnance.
fsq4cw
9 years ago
Yes, you have a gas furnace – with a 24ABC748 AC condenser that must have a matching, indoor
evaporator coil!

SR
mike_home
9 years ago
I think the OP is confused by the heat pump question since he has a very efficient gas furnace.

New HVAC & Home Energy Audit

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