Furnace & AC Replacement - 1 Stage vs. 2 Stage

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Old 01-10-18, 08:58 PM
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Furnace & AC Replacement - 1 Stage vs. 2 Stage

My home is 18 year old and I recently had a "bad motor capacitor" replaced during an emergency service by a local HVAC. The rep mentioned both furnance and A&C are old and in 'poor shape' and recommended replacement. He gave me a quote of $3,850 for Trane XL-80 100,000 B.T.U 2-Stage efficient furnace and $3,250 for Trane Xr-80 100,000 B.T.U Single stage 80% efficient furnace. He recommended the 2-stage furnace as I have a dual zone but single duct system with dampeners. He said the 2-stage will have a cost savings as the current system seems to shut off every once in a while as the furnace produces too much heat for the single zone causing the furnace to shut off from overheating. The price difference isn't too much but not sure if gas savings will warrant the 2-stage. Also, would I then need a 2-stage A/C?

York A/C H2RA060S06D
York Furnace P4HUC20N09201A
EWC Zone Controller (EWC-ST-2D)
 
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Old 01-10-18, 11:15 PM
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If you want to do zoning, you have to get 2-stage - period. Zoning with 1 stage, involves bypass ducts and cycling the furnace to avoid overheating. Same for a/c, it has to be 2-stage.


Zoning, needs to be done perfectly or not at all and it's unlikely an existing duct system can be properly zoned. Each zone needs to be able to handle the airflow of first stage.

The motor in the furnace should be variable speed ecm.. The var speed motor adjusts itself to maintain proper airflow as conditions change, and that's pretty important on a zoned setup.


Now, it sounds like you got a sales tech who wants to make some commission.

Your replace the furnace when the heat exchanger cracks or you want something more efficient. You don't replace a fully functioning furnace because it's old.

What does in poor condition even mean?

I wouldn't jump into zoning if the house has been evenly heated with 1 zone. Further, even if you do have problems evenly heating different areas, this is normally caused by badly designed air ducts rather than a "zoning deficiency".

Zoning can be a cover for poor air duct design. 2-stage, in single zone setups can be a cover for over-sizing.

Unskilled people throwing tech solutions at symptoms rather than dealing with the root causes.

If you're in a cold climate, it makes no sense to get a furnace below 90% efficiency.

Proper sizing is also really important - 100 000 btu input, 80 out is a lot; you better have a large or poorly insulated house to justify that kind of capacity.

Buyer beware.

Don't rush to replace, do your homework now, budget for it, get the heat exchanger checked a month or more before each heating season, replace when it has failed.
 
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Old 01-11-18, 05:52 AM
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You want the 2 stage a/c as well especially if doing zoning. Usually 100K BTU is oversized even for a large McMansion. 2 stage hides the problem. Oversizing the a/c is more of an issue. For both a smaller system is more comfortable as less temperature swings but takes longer to change the temp.

The estimate sounds like a low price for most areas. Still the recommendation is to get three quotes to keep them honest and for you to learn.
 
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Old 01-11-18, 07:32 AM
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Thanks everyone for the help.

Originally Posted by user 10 View Post

If you want to do zoning, you have to get 2-stage - period. Zoning with 1 stage, involves bypass ducts and cycling the furnace to avoid overheating. Same for a/c, it has to be 2-stage.


Zoning, needs to be done perfectly or not at all and it's unlikely an existing duct system can be properly zoned. Each zone needs to be able to handle the airflow of first stage.

The motor in the furnace should be variable speed ecm.. The var speed motor adjusts itself to maintain proper airflow as conditions change, and that's pretty important on a zoned setup.
Yes - I have bypass ducts (controlled by the master/slave thermostat) but I don't believe the furnance cycles because it shut down after 5 minutes (due to overheating) when the HVAC rep replaced the capacitor during the emergency visit. He indicated this probably always happens and would be fixed with a 2-stage furnance. There doesn't appear to be a 'huge' cost to upgrade from stage 1 to stage 2 but I really am not clear the benefits other than the rep saying that the furnace wouldn't shut down and being more efficient (e.g. it would run at 80% instead of 100% when zone 1 was used -- We primary use 1st zone and then heat/cool the zone 2 when sleeping)

Originally Posted by user 10 View Post
Now, it sounds like you got a sales tech who wants to make some commission.
That's the trend for all of the tech/contracts in North Jersey.

Originally Posted by user 10 View Post
Your replace the furnace when the heat exchanger cracks or you want something more efficient. You don't replace a fully functioning furnace because it's old.

What does in poor condition even mean?
Would a novice (read: not handy) person be able to determine if the heat exchanger is cracked? My only concern is that the furnance (or A/C) breaks forcing me without heat during the winter. The emergency fixed was like $450 and to exepcted more repairs given the 'poor condition'. At some point, it might make sense to replace but I just have the single cost so far. Should I just wait for it to go down completely? To be honest, I NEVER had it maintanenace.

Originally Posted by user 10 View Post
I wouldn't jump into zoning if the house has been evenly heated with 1 zone. Further, even if you do have problems evenly heating different areas, this is normally caused by badly designed air ducts rather than a "zoning deficiency".

Zoning can be a cover for poor air duct design. 2-stage, in single zone setups can be a cover for over-sizing.
To be clear, I do have 2 zones (1st floora and 2nd floor). My only gripe is the master BR (with high ceilings) heats much better than the other bedrooms but the master bedroom has 2 ducts and the other bedrooms have 1 and they have more exterior walls.

Originally Posted by user 10 View Post
If you're in a cold climate, it makes no sense to get a furnace below 90% efficiency.
Noted. Will request 90% or higher

Originally Posted by user 10 View Post
Proper sizing is also really important - 100 000 btu input, 80 out is a lot; you better have a large or poorly insulated house to justify that kind of capacity.

Buyer beware.

Don't rush to replace, do your homework now, budget for it, get the heat exchanger checked a month or more before each heating season, replace when it has failed.
North Jersey. 2 floors @ 3,000 sq. ft. with a 22' foyer and a 'baby cave' with another 1,000 or so sq ft. that's partial underground with ducts = 4,000 sq. ft total


Originally Posted by Astuff View Post
You want the 2 stage a/c as well especially if doing zoning. Usually 100K BTU is oversized even for a large McMansion. 2 stage hides the problem. Oversizing the a/c is more of an issue. For both a smaller system is more comfortable as less temperature swings but takes longer to change the temp.

The estimate sounds like a low price for most areas. Still the recommendation is to get three quotes to keep them honest and for you to learn.
North Jersey. 2 floors @ 3,000 sq. ft. with a 22' foyer and a 'baby cave' with another 1,000 or so sq ft. that's partial underground with ducts = 4,000 sq. ft total

Yes -- Will get more quotes but wanted to get some initial info.
 
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Old 01-11-18, 09:12 AM
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Okay, if it's already zoned i would put a 2-stage and the correct zoning panel that will stage properly.

With 2-stage heating and cooling, you get rid of the bypass and only allow both stages to run when both zones are on. The bypass as you've found out, along with having zone dampers closed causes furnace to over heat, cycle on limit.

I would not trust a company that would ever say it's okay to do zoning with 1-stage equipment. Better zoning panels can cycle the furnace off before it hits the limit, but it's still a bad idea.



I don't think your furnace is oversized, but when going high efficiency, drop it down to 80 000 btu/hr to put out similar output.

Multiply by efficiency to get btu output.



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You have to know what to look for to check the heat exchanger. On an 80% furnace, involves pulling the blower, crawling in underneath and checking for cracks and popped rings.

Your unit is likely to already be cracked if it's been overheated for 18 years.

The emergency fixed was like $450 and to exepcted more repairs given the 'poor condition'. At some point, it might make sense to replace but I just have the single cost so far. Should I just wait for it to go down completely? To be honest, I NEVER had it maintanenace.
Have to do maintenance, inspection of heat exchanger (you can diy most of it if u take the time to learn) once a year at this age and anything corrected. Always do it long before the start of the heating season so you have time to make a decision and aren't held for ransom.

After 25-30 years or so, may make sense to change a working furnace with no problems, but 18 is not that old.

But, if there's a problem you're trying to solve, like cycling on limit or high gas bills, yes - it makes sense to replace prematurely.

$450 for a capacitor replacement is theft - if that's all that was done. The capacitor is like $20 max - maybe $75 marked up, then maybe an hour of labour and some travel. That doesn't add up to 450, maybe 250.
 
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Old 01-11-18, 07:56 PM
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I will go with 2-stage heating and A/C if only to avoid the overheating issue. Should I request 90% efficiency/80K btu given my house size? No duct work update, correct? After this season, I will have it maintenance yearly in late fall.

Yes, $450 is high but that's the story for all contractors in my area.

Thank you for the help.
 
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Old 01-15-18, 01:00 PM
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I can't tell u for sure what to do with ductwork nor if 80 is the right size. need house construction details and calculations for that.

80k replaces a 100k 80% if you go 95%+ efficiency. Lose a couple thousands BTUs but shouldn't notice difference.

There's no point of going above what you have if it's kept up fine and unlikely 60k will do the job.

For two stage, they have to wire W2 from the zoning board to furnace, which is the control for second stage. The staging can be run off of the furnace's own circuit board's timer as is a common cost (and performance) cutting measure, need to keep the second stage off with one zone calling for heat.

Usually 100K BTU is oversized even for a large McMansion.
Not if the existing one is 80% efficiency with 100k input.
 
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