Insisting you need to replace your ducts is a well known and common scam around here.

Only one person in my neighborhood has fallen for it though.

The exhaust piping must be PVC due to the fact that the condensation is corrosive to metal pipe.

Sizing is per manufacturer instructions.

Mr duct is right.

Your Heat Pump will work wonderfully, and only when temp drops below 35, (adjustable) will propane furnace be called upon.

A long ROI considering work required to get you 5-10% better efficiency is likely his thought.

Joel, hope you are feeling better. As for Mr. Duct, seems to be unclear. My background is primarily commercial systems, so I may be missing some important insight on residential systems. The new high efficiency heat pump performance will deliver full output at ambient temps down to the teens. Dependant on the typical winter lows, auxiliary heat may not be necessary. The compressor inverter will ramp the compressor speed above typical 60 hz to deliver the output. There is a cost also to have the needed electrical circuit to power for the aux electric heat. unfortunately I do not have information showing the benefits of 90+ gas and a heat pump system verse a 80% furnace and heat pump.
You are not unclear about dual fuel. The first stage of heat will be the heat pump and if second stage is needed, the gas furnace starts. Most control logic will lockout the heat pump at the house balance point where the efficiency of the heat pump falls off and the furnace takes over.

Only a post the size of a book could straighten this clusterfuck of a thread.

You obviously haven't found the right person/company, as you have more basic questions than a first year apprentice on his first day!
But here's some information for some of the questions you have posted.

First, size the equipment per a load calculation.
If your 3 ton unit has always provided you with plenty of cooling, there's absolutely no reason to go bigger now.

Second, SEER-SEER-SEER... it's like buying a vehicle based on fuel mileage.
If your electric is expensive, get a higher SEER unit.

Third, what do you consider as stupid high pricing for LP?
Don't understand why you're not pricing HP systems.

Next, you shouldn't have a large requirement for heat, so the basic 92-95% furnace would be adequite.

Next, when outside temps get below 30 degrees, you might need supplemental heat via electric strip heat or switching over to a gas fired furnace (dual-fuel system).

Any furnace will work as backup heat in a dual fuel system. So no, you don't HAVE to buy a new furnace.

Your old ICP is 10 SEER, so any new system is going to be more efficient. 14 SEER is the minimum for NC.

Furnaces with efficiencies 82% and under are going to have hot exhaust temps, carrying the vapor to the outside before it has a chance to condense.
Furnaces with 90% and higher efficiencies are going to condense the vapor back to a liquid. Therefore, the venting must be plastic in order for it not to leak or corrode.
As far as venting size, the bigger and hotter the vent, the more wasted heat is leaving the structure.
If you retain the heat in the structure, then the venting is going to be smaller and cooler.

Also, ductwork which can move 3 ton of air, can still move 3 ton of air no matter the equipment efficiency.
Saying it doesn't, is like saying the same trailer can't haul the same load because the vehicle gets better fuel mileage.

Now, get to asking your family, friends, co-workers, church members, etc. who they use and ask if they're happy with the work they provide. Or call a couple local distributors and ask who is the best installer for the area.

^^^ referring to the OP’s last post not the above post (sorry)

There’s a lot of information there and I’ll just comment on a few. In the new homes we built yes we used smaller diameter pvc pipes and my understanding is that condensate is the reason to use pvc over metal.

In this day and age if you’re going to get a relatively high SEER unit why are you considering an old school furnace with only a 80% efficiency. All the ones we installed were in the 95-96% efficiency range.

We are just north of you and virtually every home we built had the heat pump with propane furnace back up, including my own home. In my mind it just provides for a more comfortable home, particularly in the colder months. Yes it may cost more initially but isn’t your comfort worth something?

Thanks for the updates, and the good info. And, for a man whose appendix has a date with destiny in a few weeks, I feel tip-top!

Thanks for confirming the reason for PVC is condensation. Easy to see what a problem water running back down a metal vent would be.

All these contractors were highly recommended. (Even Mr. Duct, who installed and services a friend's system for years, with no issues.)

RE: why I'm considering a lower efficiency (80%) furnace?

1) It won't be on often - paired with a high SEER, variable speed heat pump, our temps generally won't be low enough to need the furnace on frequently.

2) An 80% should use the existing through-the-roof vent, while putting in the PVC for a vent compatible with the higher efficiency furnaces will be problematic due to the system's location.

3) An 80% furnace should be more affordable than a higher efficiency model, especially factoring in the cost of putting in the extra PVC vent the higher efficiency furnaces would want.

RE: why not just go with the usual electrical emergency strips that many heat pumps come with?

Main reason is that heating with electric resistance is expensive and inefficient. We do have pretty good rates here (11 cents/kwh, generally) but still...

Secondary reason is that when on generator power, if the weather is very cold into the bargain (ice storm scenario) the higher efficiency of the furnace vs. electrical resistance strips will slightly reduce the hit rate on the propane tank.

Current thinking
Mr Duct has not provided his quote. I don't know if I scared him off pushing back on his duct theory. At any rate his ideas would lead to a) lower efficiency/SEER hardware, and b)extra costs in ductwork and vent. So I'm not holding my breath there.

Best looking proposal I've seen so far (and the way I'm leaning) is:

Heat Pump: Carrier Infinity 3 Ton 24 SEER variable speed (model: 25VNA4)
Furnace: Carrier Infinity 80% 70,000 BTU Furnace (model 58TN0)
Evaporator coil: 3 Ton
Thermostat: Carrier SYSTXCCWIC01-B with WiFi:
$15.8K installed

Current plan
Give Mr. Duct a day, then go in detail through each proposal to get to apples-and-apples. Details to resolve:
- Some bids explicitly mentioned the new thermostats, others didn't.
- One included a drain pan, When I asked, one contractor said it went against code which made little sense to me.
- Some had one year labor warranty, others two.
- Other than the one noted above, the quotes were based on American Standard equipment. Not sure how American Standard compares in general to Carrier.

I am wondering when I get in touch to resolve the details above, whether I should explicitly bring up the duct system details (20x25 intake, 12 floor ducts), in case there was any merit to Mr. Duct's concerns. That said, the contractors were all pros and they walked the same area, doing their load calcs, so they should have seen the same things Mr. Duct did.

quote:

$15.8K installed

Good God, I paid $4k for my new A/C and furnace. @11¢ per KWh I hope you are planning on that system lasting a very, very, very long time. If not, you will never recoup the $$$.

My installer said go with cheap and less efficient equipment just replace it at 10 years if need be instead of 15 years. Said since I was going from 10 SEEER to 13 (maybe 14) that I'd still be saving money, which I have. Enough to pay for the entire system after 2-3 years.

Just my personal opinion backed by decades building high end custom homes in VA.

I agree with Jesse, that price is outrageous. I still can’t fathom why you’d go with a 24 SEER unit and an 80% efficiency furnace and yes I did read your reasoning. In my years of experience the higher end units seemed to be more prone to having problems as even though they are “state of the art” so to speak they do not have a proven track record despite what the sales guy says. My firm built some of the most energy efficient homes in Virginia and we have the awards to back it up. Given that your home is (I think) more than 20 years old you will not see the efficiency potential of the unit due to the fact that your house in all likely hood leaks air like a sieve. I’m sorry to say that but that’s a fact.

Even in our homes that tested out having between 0.75 and 1.5 ACH the cost benefit analysis I did showed us that a heat pump in the 16 to 18 SEER range gave us the best bang for our clients bucks. To back that up a couple of years ago we replaced one of our HVAC units with a piggy back propane furnace in our own home. We bought a Trane XL18i and I think the cost was around $7500 using the home’s existing duct. Given that the expected life of any HVAC unit is around 20 years it is hard to see the annual cost savings coming close to the additional cost of the high SEER unit..

What size of ducting is tied to the 20x25 filter grill?
12 supply registers, what size pipe is feeding them (metal or flex?) and what size is the main truck duct?

11 cents for electric;
the only reason not to use electric is due to the (larger) generator requirements in emergency situation.

What's so special about your particular install which makes running a 2" PVC pipe, problematic?

quote:

Originally posted by Excam_Man:
What size of ducting is tied to the 20x25 filter grill?
12 supply registers, what size pipe is feeding them (metal or flex?) and what size is the main truck duct?

I'll go measure the ducts, but the input ducting is wide and short - maybe 6 feet? - as the unit is directly under the filter/grill one floor above.

quote:

11 cents for electric; the only reason not to use electric is due to the (larger) generator requirements in emergency situation.

Don't disagree - extending the life of the propane in the tank is the killer app here, with respect to the furnace. We have a significant cooling season though, SEER/efficiency is the killer app for the heat pump itself.

quote:

What's so special about your particular install which makes running a 2" PVC pipe, problematic?

The location of the HVAC for this floor is near the center of the basement, 40 feet from any exterior location. Most likely would have to blast through concrete basement wall, go through the garage, and out through the far wall of the garage, and vent right by our front sidewalk. Can't just replace the existing vent that goes to the roof two floors up, as that is also used by the propane-fueled hot water heater.

Plus, as I said, it's pointless chasing a few percentage points of efficiency on a furnace that won't be on much, if I get a good heat pump that scoops heat at lower ambient temps. We have cold snaps but don't average low temps close to freezing except Dec and Jan. Link to climate data for Chapel Hill This floor is not where we sleep, and generally the lows are at night.

11 cent power, not going to get much use, 80% doesn't need a new vent, not the floor we sleep on.... 80% furnace for the main floor still seems a no-brainer to me. Take the extra budget from the furnace and the PVC extravaganza and put it toward a better heat pump.

quote:

Originally posted by smlsig:
Just my personal opinion backed by decades building high end custom homes in VA.

I agree with Jesse, that price is outrageous.

I was a little surprised too, but it is not much higher than the 18 Seer heat pump systems from the Carrier as well as the American Standard contractors - bottom line is I have quotes from three solid contractors that do not differ much. I am suspecting at least part of this is '2021' construction mania, coupled with Biden's inflation.

quote:

I still can’t fathom why you’d go with a 24 SEER unit and an 80% efficiency furnace and yes I did read your reasoning. In my years of experience the higher end units seemed to be more prone to having problems as even though they are “state of the art” so to speak they do not have a proven track record despite what the sales guy says. My firm built some of the most energy efficient homes in Virginia and we have the awards to back it up. Given that your home is (I think) more than 20 years old you will not see the efficiency potential of the unit due to the fact that your house in all likely hood leaks air like a sieve. I’m sorry to say that but that’s a fact.

Even in our homes that tested out having between 0.75 and 1.5 ACH the cost benefit analysis I did showed us that a heat pump in the 16 to 18 SEER range gave us the best bang for our clients bucks. To back that up a couple of years ago we replaced one of our HVAC units with a piggy back propane furnace in our own home. We bought a Trane XL18i and I think the cost was around $7500 using the home’s existing duct. Given that the expected life of any HVAC unit is around 20 years it is hard to see the annual cost savings coming close to the additional cost of the high SEER unit..

For why the 80% furnace solution is a slam dunk in my application, see the post above. I'm sure your homes are well set up and insulated, and well sealed, with proper HVAC for your area. Different entire application here.

We have a surprisingly milder climate than Southern VA - the weather radar shows winter storms raining on us, and changing to snow as they cross the NC/VA border on their way north.

I can't speak to the newer designs having potential teething issues - you're probably right there. Going with a brand name with good warranty and a contractor with good labor warranty policies to help address that.

Not looking at classic payback. Good performance for 20 years, reduce use of propane with a good heat pump with good low temp heat gathering capabilities, cut the AC costs.

We did insulate and fix a bunch of door seals after a Duke Energy audit, the real issues we still have are so-so windows. But, leaky or not, even if the house is going to leak and cause the HVAC system to run longer than theoretically possible with optimal insulation/airtightness, wouldn't higher efficiency still reduce the cost of whatever running it does?

Measured the air supply duct coming from the 20x25 filter - 7 feet long, 20" diameter. 12 registers in the floor served by this system. I can't get underneath to measure ducts, but the openings the registers fit into are all 10"x4".

RE: prices.
Researching 2021 price hikes/inflation in the HVAC industry, I found this article, from earlier this month: "2021 HVAC System Pricing Continues to Rise as All Manufacturers Announce Price Increases"

quote:

Across the board, we are already seeing manufacturers raise the cost of equipment, parts, and supplies prices. Many manufacturers have made these announcements public, with increases ranging anywhere from 3% up to 9%.

The reasons for the increases are due to a multitude of factors, including raw material costs, increased labor rates, fuel and transportation costs, and changes to processes

This may explain why folks who last bought HVAC pre-COVID may be extra surprised at current numbers. There may of course also be local market conditions specific to the Triangle as our construction market is off the charts. At any event, simply replacing the dead AC unit with a SEER 14, the low bid was $6K.

So that's the baseline analysis. How much do I get for the extra spent above $6K, for going with high SEER/low ambient temp heat pump tech? Gains: Incremental reduction in power costs, remarkably better propane consumption for having much of the heating done via heat pump (vs. the 1993 furnace). Costs: more expensive.

What I'm now questioning is whether to bother with having propane backup, or just have them get rid of the old heater altogether and not replace it, and let them use the standard 'emergency' electrical heating strip. It won't get much use here, if we can get a heat pump that works OK at 35F.