2 makes the most sense to me. Certainly want to do dual fuel with your good electric rate and high gas rates. I don't think super SEER would pay so I'd skip #3. Look at the ratings, some brands can't get 14 SEER with standard blower, getting 15 SEER is virtually impossible. Don't pay for SEER you won't get.

That sounds right to me, I guess -- thanks. If that electric rate is good and gas is high, then heat pump makes even more sense. I just don't like the idea of getting heat pump/AC unit when there are more efficient models that just don't match up with our furnace. Maybe I'll try to see how old furnace is and factor remaining life into calculatiis on. Hard to know whether comfort/noise/efficiency difference significant between the older (single stage, standard blower) and newer (two stage & variable speed) systems. Complicated stuff.

Option 2 all the way. Furnace is fairly new.

New heat pump should meet the following for best combo of purchase price and low operating costs:
- 14 SEER max
- 12 EER
- 9 HSPF

Make sure that the model numbers of the condenser (outside unit) and matching indoor coil are on the quote. Post them and we'll verify actual performance ratings.

Best to you, the boss, and the one on the way.

Take care.

Thanks, Gary. New wrinkle -- Trane rep says he ran load calculation on our house and that 4 ton system is undersized for our house. I can believe it, given size & age of house and lack of insulation.

He said that our current furnace might not be able to support larger system. Coming over to do measurements & look at supply ducts, especially on 2d floor.

Does this sound right? What's the problem with the current furnace (using option 2) and 5-ton system? Is it the amount of air flow over the coil?

plan r

two problems going up in size for either AC or HP condenser.

1.ductwork has to be correctly sized both supply and return for the amount of CFMs it has to move.

ie, four ton condensers
ductwork has to be sized for at least 1600 CFMs
4 tons x 400 CFMs/ton = 1600 CFMs

for five ton condensers
5 tons x 400 CFMs/ton = 2000 CFMs

2.furnace blower has to be rated at correct size

if you need five ton AC or HP condenser, then blower has to be rated at five tons.

my advice

you need an accurate load calculation quickly so you can make an informed decision. there is always possibilty of reducing load with improved insulation

when Goodman was running, how did it cool home particularly with this recent extreme temp for our area?

IMO

Thanks, tigerdunes. When it was really hot last week (high 90s & humid), 4-ton Goodman unit did have trouble keeping upstairs cool. (This may be why it finally died, sounds like the motor bearings have gone.) I thought reason it was warm was just the age of the unit, didn't think about sizing until now.

Thanks for the good explanation about matching air volumes for AC & blower, makes sense. The contractor who was here yesterday did the load calc and said it was "pretty close to 5 tons." I'll have to nail that down more when he comes back for more measurements. Another company coming today (just getting 2 bids) & they do load calcs (also offered blower door test), so hopefully they'll also shed some light. Great info on this forum, thanks to everyone for sharing time & expertise.

Bryant contractor fixed the AC last night -- new motor, cleaned coil, pound of freon--took him about 2 hours. He was here til 9 pm on a Friday night. Owner of small company did work himself, liked him a lot. Only company around here that does blower door testing as part of estimating process, he said. Seemed a bit pricey ($755) but said would deduct that entire amount from new system purchase. If price is otherwise competitive, would be hard to say no to equivalent of $750 coupon.

Trane contractor came back today, says we'd need to replace whole system because furnace too small to support 5 ton AC that house needs per his load calc. He said calc gave him just over 4.5. Wondering if I can improve that with more attic insulation, better storm windows, etc.

His rough estimate for new AC and 96% furnace, Trane, all new ductwork, was $16,000. Ouch. Just bought this house, wish we had asked for more $$ for HVAC repairs... He says we'll need all new ductwork because it's in partial basement/partial crawlspace and stuff we have now is leaky and uninsulated. Having him do 3 estimates -- AC/gas furnace, heat pump only, and dual fuel.

Do some hard figuring before spending your money.

What investment will be the most cost effective for both heating, cooling & dehumidifying your home.

We could cut residential heating and cooling equipment size in America by 30% to 50% if Contractor's would perform honest Manual J calculations and provided full credit for every load reducing element or detail they can do, when doing the calculation audit. Additionally, load reduction remedial actions should be provided as options toward further reducing Air Conditioning and heating equipment sizing.

Down sizing has many advantages; the existing duct system & air handler will function more efficiently helping to achieve the unit's nominal tonnage capacity with less than peak heatload conditions. That improves EER & SEER performance.

Energy costs will probably keep going up therefore reducing the year-round heatload makes sense. - udarrell

Here is a link that might be useful: Downsizing Is Cost-Effective

"He said calc gave him just over 4.5. Wondering if I can improve that with more attic insulation, better storm windows, etc."

YES!!!!!!!!!
Increasing attic insulation, better windows, storm doors, caulking, etc all reduce the heating/cooling load on the system. You can have the Manual J heat gain/loss calc redone with your proposed energy savings upgrades and see if the system sizing is reduced. Just a thought before you spend big $$ on a new system.

Good luck.

Helpful site, Darrell. I'm hopeful that the other company will come in lower & give us ideas on reducing load to downsize system. It's 4 tons now, and even with 20 year old AC it cools most of the house well except hottest days, and that problem seems mostly airflow-related (no returns upstairs). I'll look into quotes on insulation/upgraded storm windows, too.

If your ducts are leaky and uninsulated, fixing that problem alone may be enough to make a 4 ton system work. Not to mention the overall energy and cost savings and that it's just the right thing to do.

for plan r

If operating costs are important to you, and based on NC location, it would be a mistake not to leverage reasonable electric rates with a high eff heat pump or dual fuel system.

IMO

run the numbers on attached fuel comparison calculator

Here is a link that might be useful: Fuel Comparison Calculator