Thanks for the reply. The furnace is in the attic (we are on a slab). They did say that our options were limited by the size of the opening into the attic, and the extra cost we would incur in rejigging that to allow us to get the unit up into the attic space- which would reduce/eliminate the cost benefit of the efficiency improvement.

I agree though and have asked the company for info on > 80% options (my understanding is that they are required in some parts of the country though not - yet - in the southeast).

I'm curious as to the degree to which these choices would affect resale value of the house but I get the sense that most buyers aren't concerned about those details - in which case the more basic system would be fine (this is not our 'forever' home).

The minimum requirement in the US is for a 80% efficiency furnace. There was an attempt to increase it to 90% several years ago but it did not make into a law. The minimum SEER rating for North Carolina is currently 14. The new SEER minimum for your area will be 15 in 2023.

The 80K furnace seems over sized for your house and area. Is this the size you currently have? Is so does it run in short cycles? A 95% efficiency furnace would be nice, buy you have to consider how long you plan to be in this house versus the time to recover you investment. Find out if a higher efficiency furnace would qualify for a utility or state rebate.

I don't think a higher efficiency furnace will affect your resale value. However a high efficiency 2-stage AC would certainly be more noticed by buyers. It will also provide better humidity control which I think is important for your area.

The 80% EER is a typo. Find out the correct value. EER is an important indicator of efficiency in hot climates in my opinion.

Thanks- very useful. Online it says that the a/c unit for option 1 is UP TO 15 EER and 19 SEER, so I'm guessing the 17 SEER stated by the company who made the quote is based on the actual value we would get with the specific combination they suggested. Option 1 all in is about $8700 (condenser + furnace + coil )

Option 2 is stated online as 11.7 EER and 14 SEER but with the equipment combo quoted is is measured at 12.25 EER and 14.75 SEER, so within limits until 2023. Presumably legislation on minimum specification requirements only applies to installation of new equipment (i.e. it doesn't require upgrading any existing equipment)? Option 2 all in is about $6500

Our existing a/c unit is marked PA13NA03600GBAA, I can't find this online but similar units are all 10.5-12.2 EER and 13 SEER. This unit was installed only about 7yrs ago so looks to have been a replacement for the original system that was installed when the house was built. We know the a/c unit does have a slow leak somewhere, otherwise we might keep it.

Our existing furnace is a P3HUA12N04801C, which is 20yrs old and all I can find online is that it's 57,000 btuh input and 48,000 btuh output and 80% efficiency. So yes that seems like a huge difference? I'm not sure I can tell if it runs in short cycles, when it comes on it probably runs for 2mins before cutting out.

We WOULD get a rebate on a 95% efficiency system but it seems overall we would not get the benefit of that given the increased cost and likely time in this house. I checked with the local company and they said that it would require new flue pipes and possibly some roof work- so it looks as though we should stick with 80%.

Our house is in a high demand area so it's not hard to attract buyers, from what I can tell most buyers are more concerned about the cosmetics.

Thanks for your help- much appreciated

The SEER rating is determined by a specific combination of condenser, furnace, and coil. The manufacturer provides the values and has to guarantee all combinations will meet a minimum SEER value. That is why you see the words "up to", or a range. The installer should give you the AHRI certificate of the SEER and EER rating. You can also look this up yourself on the AHRI directory site if you have the patience. New rules on HVAC equipment usually specify when newly manufactured equipment has to meet the minimum standards. Y don't have to worry about this.

If the current furnace only runs for two minutes, then you definitely want a smaller size. It should not be a problem to pair with a 3 ton condenser and coil.

Have you gotten an estimate to fix the current leak? Given the equipment is only 7 years old this may be a good option if you are planning to move within 5 years.

One issue with an attic mounted high efficiency furnace in our climate is condensate pipes freezing and rendering the furnace inoperable. We have two 95% furnaces, one in the attic and one in the crawlspace. The crawlspace furnace has been fine for 13 years, while the attic one freezes every so often. This has caused us much grief over the years - we have one heat tape on the attic drain and a second on the outdoor drain, but it still freezes in the exterior wall occasionally.

Does York make a 60,000BTU 80% furnace? Thst would seem more appropriate to your home, although if its short cycling now, that could still be a problem. You need them to do a heating load calculation, given the questions on sizing.

The answer from the local company that did the quote was that the 80,000BTU would warm up the house faster, and they like to match the a/c (36,000 BTU), coil and furnace so as to reduce necessary turbulence in the transition and not add problems in the air flow. Does that sound about right?

A larger furnace will recover from temperature setback faster than a smaller one. However it is not worth over sizing the furnace. Even if you wanted to do this, you would have to verify the duct work is large enough to handle the increased air flow. This is a bad idea.

I don't understand the comment "to match the a/c (36,000 BTU), coil and furnace so as to reduce necessary turbulence in the transition and not add problems in the air flow". The only thing I can think of is the width of the 3 ton coil may be 21 inches, and the width the 60,000 BTU furnace might be 17 inches. In a case like that the installer builds a transition duct to accommodate the difference in widths. He may be selecting an 80,000 BTU furnace which is 21 inches and thus avoiding to have to build this transition. That would be a bad way of doing it in my opinion. If that is the case tell him to find a coil that is the same width as the furnace or build a transition duct. I have this situation on one of my furnaces and coils. The transition duct was installed and it has worked fine,

Thank you- I have seen several sites warning against oversizing for the reasons you suggested. What you said about the transition also makes sense. One other point that might be relevant is that we already find there are rooms that heat really well and others that don't, and my reading tells me that oversizing can exacerbate these differentials and could make it even harder to get a good balance throughout the house.

The company has a great reputation in the area and we've always found them to be very reliable in the past for servicing and tune-ups so there may well be aspects we haven't considered. We will probably hold off on this for now until I can get some additional quotes.

Thank you everyone

Have you considered a 2 ton AC condenser/coil? We have 2 floors (~1500 sq ft on each floor) with a 2 ton AC condenser on both floors. Never had an issue with cooling or dehumidification - we're in central NC (Triangle). Two 60,000 BTU furnaces have been fine for the coldest winters.

EDIT: Cold and hot rooms point to an issue with the ductwork.

Interesting- we're in the Triangle too, and have been fine with the winters thus far.

I did wonder that same thing - i.e. should we match everything 'down' rather than 'up'? That was never suggested as an option, maybe because we currently have a 3 ton unit.

I'm also thinking that if the cold vs hot rooms is down to ductwork, having a more powerful furnace could make it worse rather than better?

We timed some cycles today- generally 4-5 mins before the furnace shuts off, when maintaining a constant 70degC