My AC has gone to meet its maker.

I am definitely replacing it, most likely also replacing the existing heater (1993 vintage).

I got some proposals from the folks I generally use, but the guy they have shepherding the proposal seems rushed and not very detail oriented.

So, I am not going to proceed until I know for myself the proposed systems are the right size and type to exactly replace the failed/old systems's HVAC performance - (i.e. - the old ones were sized correctly and gave no problems.)

Any if any experts can share their thoughts, I'd like to have any ideas you can come up with.

Background

Tons/BTU rating:
The proposal writer tells me (color me skeptical) that I don't need to worry if the ton rating is more than the old system. Knocking around the back of my brain is a possibly outdated(?) concern that too many tons could get the job done too quickly, risking freezing up the system and maybe also resulting in the system not staying on long enough to take humidity out.

The proposal-writer intimates that the installers can adjust for lower BTUs/Tons during install. 1) is that true, and 2) what are the ramifications.

SEER/AFUE:
We see pretty heavy AC usage - not as bad as Texas/Florida, but we burn a lot of electricity in the summer. Heat is fueled by Propane which is stupid expensive. Really wish our neighborhood was set up for Natural Gas.

SEER
The range of SEERs proposed was between 17 and 14. Other than the power consumption improvements, are there other aspects resulting in different SEER ratings we should look for/avoid? All things being equal this one I'm thinking of maxing out (assuming that doesn't wind up messing things up)

AFUE:
The AFUE ratings in the heating units being proposed ranges from 92% (1 stage) to 96% (two stage) I'm sure these are way beyond the efficiency of the current 1993 heating system, and I'm probably leading toward one of the 92% choices. Am I being shortsighted?

Any other relevant thoughts welcomed.

My next task is to go get model numbers for what I already have, and see what ratings they had.

Bigger isn't always better.
I say he installer is more important than the brand you choose.

Oversizing the unit isn't a good idea, been expressed here by the HVAC gurus several times

Seer is the efficiency rating for the ac, higher the number typically the more efficient the unit, best to get the highest number in your affordability range since you run AC more than anything else this would be a good area to focus your investment, JMO.

You might consider getting a quote on a heat pump that's electric vs propane if you want to eliminate the LP cost factor.

Lots of other factors go into it, I'd get several quotes from local AC companies and see who offers up a reasonable quote and better inspection of your existing system.

Around here, we use the AC for a good portion of the year; not just in days but also for considerable temperature reduction (ie = 30 degrees of reduction). Relatively low humidity. So, I would size accordingly to fit the needs which may allow for higher tons. And not sure about SEER rating - would consider costs and also diminishing returns of efficiency to output.

Interested in the thread as I believe my AC is undersized (and low seer) - it runs more than I think it should and the differential is lower than I'd like. But it's complicated figuring tons vs seer.

Watching this thread as I think our AC is overdue (20 years now), just like the water heater.

There is honestly too much to address that is wrong with what you are being told.

You need another person to come out and look over what you have.

Sizing the system based on the ductwork you have in existence at very least.

In a nutshell, too large a system will cool too quickly, and in NC, that will leave you feeling cool and damp.

If duct work is not allowing enough airflow, then you will have liquid going back to the compressor, and damaging it, mechanically by incompressibility of liquids, or washing the oil out, either way, it will greatly reduce the lifespan of your unit.

Heat pumps have come a long way, I would consider a dual fuel system in your area with automatic changeover to propane. Cost is marginal in initial expense, will see great dividends after a few months of not using propane to heat your home.

The fancier the system, the less likely techs will have parts for repairs on their van in future... I like to keep it simple.

How long can you survive with your system down between repairs? Do you see below zero for several days straight? Above 100?

That drives how simple I like to keep it.

I'll preface this by saying that I am not an expert. I have lived in 2 different houses and replaced the HVAC system in both.

Regarding cooling BTU
The contractor installing the new air conditioner should do what is known as a "Manual J" calculation for your house. They should walk around your house taking measurements of the rooms, windows, doors, insulation in the attic, maybe more. That is what I remember from getting ours replaced about 5 years ago.

That information is used to calculate how much cooling load your house needs. I had 4 contractors quote the job and only 2 did the calculation. The other 2 sized our house for a 5 ton when the calculation yielded 4 tons. More is not better as you said, it doesn't run long enough to remove the humidity.


SEER/AFUE
There are calculators on the web that can be used to see if/when you see any savings from the increased efficiency of higher SEER. Naturally the higher efficiency units cost more up front. Electricity where I live is not crazy expensive and I've not noticed any significant change in my electricity usage. At the time the manufacturer was offering 0% financing on the higher SEER unit, which ended up being the deciding factor.

My inside unit (air handler) is 20 years old. My outside unit is about 10 years old. Currently when it is stupid hot, they can only cool things so far, down to about 76 degrees or so. I know they will go one day based on their age and when they do, here is what I will tell the contractor: When it's a July day, and it's 95 degrees and 85% humidity, and the sun is shining at 3pm in the afternoon, if I want it to be 70 degrees inside at that time, that is the type and size of system I want you to install. I do not care to know the tonnage, the SEER, the BTU's or any other technical info. What I want is that when I turn the Nest down to 70 degrees, it gets to 70 degrees in my house regardless of what is going on outside.

Just a quick explanation of SEER:

For any given SEER value you multiply your tonnage times 12,000 BTU (12k is one ton), then divide by the SEER. This yields the consumption in watt hours of the system.

ex: a 3 ton 16 SEER would work out this way - 3 x 12k = 36k -> 36k / 16 = 2250 -> 2250 / 1000 = 2.25kw
In the above example, if the system ran for 1 hour, it would cost you 2.25kwh multiplied times your given electricity rate. If you pay the nationwide average of ~ 12.4 cents per kilowatt hour it would cost ~ $0.28 for that 1 hour cycle.

Anyway, the idea is the higher the SEER (divisor), the lower the energy cost.

That's how SEER math works.

quote:

For any given SEER value you multiply your tonnage times 12,000 BTU (12k is one ton), then divide by the SEER. This yields the consumption in watt hours of the system.

Thanks! This is useful - never knew this before.

I replaced my 18 year old AC a year ago and the only thing I changed was going from an older unit to newer technology and going from 14 SEER to 16 SEER.

My Electric bill dropped by $360.00/year.

1993 vintage-what is your refrigerant? R22 was still in use at that time. New refrigerant proposal may warrent replace old condensor, lineset and Air Handler.

I also believe installation can be important. Be aware that if a one man shop installs it and then the tech is put out of commission, you be SOL.

This message has been edited. Last edited by: oldbill123,

There are pitfalls, believe me.

The "proper" way is to have a contractor perform an independent home load analysis. Here, the contractor will draw the home up, measure the windows and doors, orient it to the compass, etc. Then, given your location, he will calculate the thermal load you have to cool the home.

This analysis is based on data for your location for average temperatures. That is one pitfall. If the chosen temperature on which to base the thermal load is wrong, then the calculations can be wrong.

The home has existing ducts, and many times an estimator will say "are you happy?" If you are, he assumes that you have adequate flow and return in these ducts. This is another pitfall. You can, if you want, measure the outlet of each register in square inches, the return duct size in square inches, and estimate the tonnage required to move that much air. However, of course, this assumes that the original installation is ideal and correct. Probably not.

So, given what ducts you have, you must make an informed decision on changes you need to the ductwork for a calculated thermal load. Then, from that analysis, including the duct changes, and the thermal load, you can find the ideal size unit.

Once you have the thermal load, then you can decide on how efficient you want to be. SEER.

Installation quality is paramount. Choose contractor wisely. Be firm in your assessment. Move the unit from vertical to horizontal if need be. Ensure the new unit has drip pan, float valve, overflow protection, etc. to the new codes. Consider replacing your old line set with a new one, as these can and do leak.

All good points mentioned here. A professional will perform a heat load calculation along with the survey. I'd get two more estimates. Food for thought, what will be the ROI between the efficiencies? I'm on propane also, and my 93 system is nearing its end also. I would consider a dual fuel system ( Heat pump with gas heat ). I am looking at the Bosch system. 22 SEER variable capacity for good dehumidification control. And as usual, the most important thing is a proper installation. I see you are in NC, not sure how cold the typical winter gets where you are at, but if you are staying above 32 and utilize a higher efficiency heat pump, may consider saying bye bye to the propane man. The only downside is generator power for heat when the power goes out.

What is the actual size of the equipment you have? How well was it doing the job for you when it was working properly? We are looking at replacing our propane furnace and central air conditioner with new equipment and will go back with the same size we had which was doing the job nicely. If you have issues with the comfort of your present equipment when it was working properly then you need to look at changing the size of the new equipment and/or duct work.

Thank for the inputs, please keep them coming.

I love the idea of a high efficiency duel fuel electric/propane heat pump! Any downsides to that?

I have a bit of research to get details on the 1993 installed stuff, size, ratings etc.
I should have that done by tomorrow.

The AC was R-22 based; that was part of the reason to dump it. Would have cost a heckuva lot to fix the condenser leak, and another boatload to reload the R-22 and hope the fix held. Probably out $2K to get to that point, and then (assuming it held) I'd be back to the status quo of a 1993 system.

[QUOTE]Originally posted by joel9507:
Thank for the inputs, please keep them coming.

I love the idea of a high efficiency duel fuel electric/propane heat pump! Any downsides to that?

Downside is initial cost. The last time I looked at comparison between high efficiency and standard systems, I found the payback was rather high. If you plan on staying in this home, go for the highest you can afford. Another consideration will be possible future repair costs. New high efficiency inverter units have expensive electronics. So check the warranty and consider having a surge suppressor installed on the power to the unit to help protect the circuit boards.
Yes, R22 prices are increasing, making the decision of repair or replace simple.

Replaced SEER 14 with a new SEER 14 Carrier Heat Pump. Old one had the infinity indoor air handler and Infinity thermostat. New unit doesn't dehumidify nearly as well and I may now have to add another dehumidifier. (have a dehumidifier in the crawl space) Indoor humidity is likely above 50. Have 4 humidistats and each gives a different reading. If humidity is an issue be sure you check on the air handler side of things

Getting back online now, had an episode with what turned out to be appendicitis last week. That can sure wreck a schedule!

RE: Dual Fuels - was(am) I confused?
I may have gotten the wrong impression from the dual-fuel suggestion. My (possibly befuddled) thinking was that instead of relying on the usual electrical heaters built into the heat pump unit for emergency heat when the outside was too cold for the heat pump, there would instead be a propane heater built into the heat pump unit.

Going online to look at options, I kind of struck out. What appears to be the usual method there, in contrast, is to slave a separate gas furnace to the heat pump, and have the heat pump control that separate heater and just skip putting in the electrical heater into the heat pump.

There are some preconfigured/packaged systems done with integral propane heat panels inside, but those don't appear to be very efficient overall, kinda entry level designs where space is a premium, or ultimate low cost of installation trumps efficiency.

So, two followon questions:

1) Are the good, high SEER dual-fuel heat pumps all going to need a separate heating unit?

2) If so, will I have the option to keep the old heater or do they require a new, compatible furnace to be installed at the same time?

Re: older system
Dead AC: Inter Cities Products/Heil 5536 (10-11 SEER)
Working (but old) heater: still working on getting model info. Apparently I have to remove some plates to see this.

Four of the four companies have come and looked, and each had different takeaways.

Last one (this morning) focused on ducts. For convenience, let's call him "Mr. Duct". Said the duct system I have with a 20x25 filter size (that has worked for my 1993 3-ton system with no issues) is inadequate for a variable speed system, so he isn't quoting the good variable speed high SEER heat pumps - says they wouldn't work. Also said that the 4" steel vents I have cannot be used with a 90% efficient furnace, (which I'd presumably need, with a single speed heat pump) and that a smaller diameter PVC vent has to be used and that it's OK for that that new PVC to vent mostly horizontally vs. vertically.

None of the other three companies complained about existing ducts/vents. I don't know if this last guy is out to lunch, or whether the other three were. I do know that there would be a lot of auxiliary cost to do the new ducts/vents and that I'd wind up with a less efficient system and more propane consumption around his approach. Haven't seen his numbers as yet.

All four are serious, stand-up companies who provide at least a 1 year labor warranty on stuff they install, wrapped around the factory warranties (10-12 years) on the hardware.

What it's looking like (unless Mr. Duct is right, and the other three are wrong) is a high-efficiency 18-20 SEER name-brand variable speed heat pump, backed by a variable speed 80% propane furnace.

Anyone with thoughts on that approach (and whether I should pivot around Mr. Duct) please chime in.

For bonus points--------------------------------
1) If anyone can verify the reason(s) why, if I went for a high-efficiency furnace, the new furnace couldn't use the existing 6" flue vent. My takeaway from Mr. Duct was that going PVC had to do with managing condensate from the exhaust. Is there more to it than just the condensation?

2) Supposedly in Mr. Duct's scenario, the new PVC exhaust pipe would be a much smaller diameter than the existing exhaust vent. Given the exhaust from the furnace will be cooler due to the second pass, I would have thought wider diameter would be easier to vent. (But I'm not an HVAC engineer, just an old Mech E.)

There's probably a very good reasons for both of the above but Mr. Duct's techs kinda relied on 'code' and 'manufacturer installation procedures' with no rationale beyond that. I would appreciate the thoughts of anyone understanding the underlying thinking here.