Replacing furnace/ac - opinion

[mlcarson]

My house was built in 1987 and has the original furnace and AC. The furnace was a Magic Chef 6A100D 100K BTU (mfg 1985?). The air conditioner is a Energy Knight/Comfort Air QCE-24 (2-ton). The house is a quad style with each section around 572 square ft -- if you count just 3 sections that's 1716 square ft -- the last section is underground and is where the furnace/utility room is. This is in mid-Michigan. The furnace is starting to have little issues -- blower is causing duct vibration, pilot not extending far enough to always hit flame sensor. Air conditioner was recharged at the beginning of last year and froze up by the end of the year so apparently has a freon leak. I don't think these are major problems but given the age of the system, I'm inclined to just replace it with something more efficient.

Quotes so far are:

Company 1A - base price
Goodman GMV950704CX - 70K 95% 2-stage Variable speed
Goodman GSX130361 - 3 ton 13 seer R410A

Company 1B - 50% more than 1A
Trane TUY080R9v3V - 80K 95% Variable speed
Trane 2TTR3036A1000A - 3 ton 13 seer R22

Company 2 - 15% less than 1A
Rheem Classic Furnace - 60K 95% 2stage
Rheem Classic AC - 2 ton 13 seer R410A

Company 3 - 14% more than 1A
Carrier 58MXB080 (comfort 92) - 80K 92% 1 stage
Carrier 24ABA330-3 - 2.5 ton 13 seer R410A

Company 3 told me that a 60K furnace was just a bit too small according to their calcs so went with an 80K -- the next size up.

My current AC seemed to have trouble keeping up with cooling demands even when fully charged on hot days which seems to give company 3's figures some credibility. I'm leaning toward option 1A on a price/feature basis.

Anybody want to give an opinion? Have I given enough information to be useful?

[21degrees]

Quote 1 stat away from he is not sizing equipment right. Option 2 is doing same thing too small option 3 looks like he has sized it properly.
My house was built in 1987 and has the original furnace and AC. The furnace was a Magic Chef 6A100D 100K BTU (mfg 1985?). The air conditioner is a Energy Knight/Comfort Air QCE-24 (2-ton). The house is a quad style with each section around 572 square ft -- if you count just 3 sections that's 1716 square ft -- the last section is underground and is where the furnace/utility room is. This is in mid-Michigan. The furnace is starting to have little issues -- blower is causing duct vibration, pilot not extending far enough to always hit flame sensor. Air conditioner was recharged at the beginning of last year and froze up by the end of the year so apparently has a freon leak. I don't think these are major problems but given the age of the system, I'm inclined to just replace it with something more efficient.

Quotes so far are:

Company 1A - base price
Goodman GMV950704CX - 70K 95% 2-stage Variable speed
Goodman GSX130361 - 3 ton 13 seer R410A

Company 1B - 50% more than 1A
Trane TUY080R9v3V - 80K 95% Variable speed
Trane 2TTR3036A1000A - 3 ton 13 seer R22

Company 2 - 15% less than 1A
Rheem Classic Furnace - 60K 95% 2stage
Rheem Classic AC - 2 ton 13 seer R410A

Company 3 - 14% more than 1A
Carrier 58MXB080 (comfort 92) - 80K 92% 1 stage
Carrier 24ABA330-3 - 2.5 ton 13 seer R410A

Company 3 told me that a 60K furnace was just a bit too small according to their calcs so went with an 80K -- the next size up.

My current AC seemed to have trouble keeping up with cooling demands even when fully charged on hot days which seems to give company 3's figures some credibility. I'm leaning toward option 1A on a price/feature basis.

Anybody want to give an opinion? Have I given enough information to be useful?

[BaldLoonie]

You have a 2 ton and say nothing about it not cooling the house all these years yet many of your bids want to put in a 3 ton? Bigger is not efficient nor does it dehumidify well.

Go find the thread about a NOISY system where his installer greatly upsized the equipment!

Also 80,000 BTU 90+ furnaces want to move a lot of air to keep from overheating. Hope you have the duct size for it.

[skippedover]

You're gambling several thousands of dollars on this new system. I'd recommend doing your homework thoroughly to remove much of the risk.

[2old2rock]

Find someone that will perform a load calculation. And have the ducts sized to match the needed cfm.

[platchford]

Did any of these contractors perform a load calculation on your system? If not, then they are all simply guessing which is a poor way to replace a system. Make sure a load calculation is performed and that they also check to make sure the ducts are able to handle the supply from the new furnace. If the contractors skip performing a load calculation then that leaves a lot to be desired. There are many things that may have changed since the house was built over 20 years ago... additions, new windows, attic insulation, etc. All of these impact the proper system size which is why a load calculation (or Manual J) is needed.

[mlcarson]

I DID say that the old 2-ton was not adequately cooling the house on hot days. The old furnace is 100K BTU -- but probably 60-70% efficiency. Not sure what the duct size is at the moment but are you saying that the duct size has to be larger for a lower BTU furnace?

The problem I have is how the heck do you figure out the good from the bad places. The quotes were from well-established - 20 year local companies. I get to deal with the sales type guys for these quotes -- not the actual installers so how do you sort the good from the bad on a project that only gets done once. It's not like I get to use them all once and judge their performance.

I could have done the sizing as well as these guys not knowing anything about HVAC. 100K BTU -- 60% (figuring probably somewhat oversized) = 60 to 80K BTU @90+%. 2 ton AC not quite doing the job -- go with 2.5 or 3.0 ton. All I saw them do was take some room measurements -- look at the existing furnace/ac/ducts -- check the circ panel -- and come up with a quote some time later.



You have a 2 ton and say nothing about it not cooling the house all these years yet many of your bids want to put in a 3 ton? Bigger is not efficient nor does it dehumidify well.

Go find the thread about a NOISY system where his installer greatly upsized the equipment!

Also 80,000 BTU 90+ furnaces want to move a lot of air to keep from overheating. Hope you have the duct size for it.

[aircooled53]

You're gambling several thousands of dollars on this new system. I'd recommend doing your homework thoroughly to remove much of the risk.

Most of the statements that are in that pdf file you gave are true, but let me ask you one correct thing and see if you can answer it.


Are you going to tell him that your design is better than what he has spent the last two weeks researching?
What do you do when a customer tells you he wants 3.0 ton system and 80 btu furnace and Vision Pro thermostat and new line -set.
If so you will loose allot of qoutes...

Just an opinion with factory trained Hvac design and build technician with ACCA,NATE, and 30 years in the trade in new construction and retro fit systems.

[21degrees]

I try and educate but some customers tell, my presentation was very thorough but they 2 other guys telling them they need a bigger unit and I try and tell them about proper humidity removal, they say lets just go with bigger unit. So I say more money in my pocket to their faces. I also tell them the unit will not last as long.
Most of the statements that are in that pdf file you gave are true, but let me ask you one correct thing and see if you can answer it.


Are you going to tell him that your design is better than what he has spent the last two weeks researching?
What do you do when a customer tells you he wants 3.0 ton system and 80 btu furnace and Vision Pro thermostat and new line -set.
If so you will loose allot of qoutes...

Just an opinion with factory trained Hvac design and build technician with ACCA,NATE, and 30 years in the trade in new construction and retro fit systems.

[heatplanman]

any experienced contractor would agree that they are tired of being an unpaid consultant to the customer seeking several bids. first don't repeat someone else's mistake. customer may want bigger equipment, but the duct size can only handle a specific amount of cfm and no more. i'm not being paid to educate in the bidding process. i want to sell trust and confidence first. every experienced contractor has many war stories. i stick to what my experience has taught me. i present a system and options that i'm confident in and that's it. and i keep in mind the old 5-5-90 rule...5% love you 5% hate you and 90% don't care one way or the other.

[heatplanman]

i do a personal load calculation on any retrofit that i do. i won't present it to a customer unless i'm paid for it. on the retrofit i have existing duct sizes, existing insulation throughout the house, existing window sizes and quality, and existing facing exposure of the house. why should i give away a complete load analysis. my time is worth something. i don't want to end up making the same mistake that the installing contractor may have made. if a 4ton system can't handle the bedrooms in a 2 story colonial. a 5 ton system won't fix the problem either. if the duct work can't handle the static pressure of a 5 ton system, then i'd lose in the end. i'd have either a major sevice headache or i'd have to listen to an unhappy customer saying that the bedrooms are still uncomfortable.

[platchford]

I DID say that the old 2-ton was not adequately cooling the house on hot days. The old furnace is 100K BTU -- but probably 60-70% efficiency. Not sure what the duct size is at the moment but are you saying that the duct size has to be larger for a lower BTU furnace?

The problem I have is how the heck do you figure out the good from the bad places. The quotes were from well-established - 20 year local companies. I get to deal with the sales type guys for these quotes -- not the actual installers so how do you sort the good from the bad on a project that only gets done once. It's not like I get to use them all once and judge their performance.

I could have done the sizing as well as these guys not knowing anything about HVAC. 100K BTU -- 60% (figuring probably somewhat oversized) = 60 to 80K BTU @90+%. 2 ton AC not quite doing the job -- go with 2.5 or 3.0 ton. All I saw them do was take some room measurements -- look at the existing furnace/ac/ducts -- check the circ panel -- and come up with a quote some time later.

If the companies are not performing a load calculation then I would be hesitant to call them a 'good company.' Now, that is not to say that a company couldn't perform a load calculation and still be a 'bad company' but your odds are better. It is not a difficult task to perform a load calculation... while I understand others thoughts about disclosing the actual specifics of the load calculation until the agreement is signed, it does not negate the fact that a load calculation must be performed before a 'good company' can give a quote. How can you give a quote if you don't know what size equipment you are installing? The proper way to do that is with a load calculation.

Your logic on upgrading the AC size is ok but how do you know for sure that the existing system is still operating at its original 2 ton rating? For all you know it worked fine when it was installed 20 years ago and in time the indoor coil has become dirty and capacity has dropped... just a thought... that is why you want a proper load calculation... you're just guessing otherwise. The same goes for the heating system... it was 100k BTU unit... you're guessing at its current efficiency but who really knows? Is its effective capacity 50k, 60k, 70K or more?

So, make sure any company you consider performs a load calculation... you can ask this in advance over the phone. That will help to weed out the less desirable companies. You can also ask for references or ask friends and families for recommendations.

As for your current quotes, I would lean heavily toward an R410a system rather than an R22 system. I would probably pick the 2.5 ton rather than the 2 ton or 3 ton but, again, that is just an 'educated' guess based on your statement. You could always ask Company 2 to adjust their quote based on a 2.5 ton and maybe a 70k or 80k furnace. You could ask 1A to quote a smaller AC system. I mean, based on guessing I would say Company 3 would be close... but who is to say they are the better installer and not just the better guesser and why just a single stage furnace?