I Can Only Do 80% Due to Flue Situation - Which Furnace?

ak0402November 26, 2011


I need to replace my 20-year-old furnace. I live in Chicago, in a townhome development built in early '90's. My townhome is 3 stories, about 2000 s.f., attached on each side, no basement. Wall insulation is good, but there are significant drafts from the large windows. The thermostat is a Honeywell 7-day programmable, about 7 years old.

Funds are too short to replace the AC too, so just the furnace. The existing furnace is a Carrier, 110,000 btu's, 80% efficiency. The company who has been doing my maintenance for the last 7 years gave me a quote. They only install Carrier (which they've been working with since 1957). They had done a load calculation too, and the 110,000 btu's is appropriate.

I don't have a basement. And, if I tried to run a new PVC flue out the back of the house, it would be venting into a common area of other townhomes, which is prohibited by Chicago Code. So I need to use my existing metal chimney. Therefore, I cannot install a 92-95% furnace.

I won't be eligible for tax credits from Fed, local gas company or state. But I will save on the upfront cost of purchasing an 80% furnace. I will be getting a 2-stage furnace, but I do not want a variable motor. The salesperson admitted he won't be the lowest bidder, because of "their installation expertise, quality of technicians, knowledge, customer service, and years of experience in the business". Anyway, their quote was $2600 for the Carrier Performance 80 2-stage furnace, manufacturer's warranty (one-year on parts and labor, 10-year on parts, 20-year on heat exchanger).


- Should I be looking at York also, or another brand?

- are there are good brands which will be more efficient than 80% (like 85%?) while still not requiring a chimney replacement?

- Is $2600 very high, given that I live in Chicago?

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I am sorry. I simply don't believe that load calculation for a 2000 sq ft internal TH unit.

I would want to see it in writing on the software's letterhead.

And BTW, what size is the AC condenser you intend to keep?

Post back.


    Bookmark   November 26, 2011 at 2:08PM
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Tigerdunes - AC condenser is 4 tons, which was installed when the home was built in 1991. I am not a big AC user; it needs to be really hot before I turn it on.

I should have said 2200 s.f. Also, there are very large drafty windows (two are 12' wide by 9' high, and master bedroom has entire 18'-wide wall of Pella windows (don't get me started on Pella, that's for another Forum)). I will have to ask for the load calculation in writing.

    Bookmark   November 26, 2011 at 2:21PM
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to answer your questions:
Yes York is also another very good brand to consider. The expertise of the installer is also important, so don't go necessarily for low bidder.
Ask about warranty, and make sure you get something sized for eventual AC replacement.

Not that I know of.

Probably not.

    Bookmark   November 26, 2011 at 3:56PM
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"The expertise of the installer is also important"

At least as important (and maybe more important) than the brand.

    Bookmark   November 26, 2011 at 5:40PM
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It sounds like you have a lot of glass, so the heat load may be higher than expected for a townhouse of your size. I would still ask for the load calcualtion.

You are not going to find a high efficieny furnance which can be vented through a chimney. The $2600 price is not bad in my opinion. I am not sure your Honeywell thermostat will be able to work properly with a 2-stage furnace. Ask the contractor about this.

It is a good practice to get additional guotes. The Carrier Performance 80 is a good furnace. If you have confidence in this contractor, than go with him. The only other suggestions I have is get a 4 inch media filter and the Carrier 10 year labor warranty.

    Bookmark   November 26, 2011 at 7:45PM
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Mike_home - thanks for your advice. The furnace is in a small closet off of a ground-floor den, and there is no room for a 4-inch media filter. Also, I had inquired about the Carrier 10-yr. labor warranty, and the contractor quoted me $480 which I thought was crazy. He seemed reluctant to sell it to me, even if I really wanted it. He said most of his customers opt not to get it.

I have to say that in the 7 years I have lived here, my current 20-year-old Carrier/Bryant/Payne furnace has only needed an ignitor replaced, and no other repairs. It now has some hairline cracks in the housing, which is why I have to replace it.

Also, besides the 110,000 btu, the new furnace he quoted me is 1600 cfms. The same model also comes in 1200 cfms, but the contractor told me that wouldn't be enough to push my air (can't remember if he said AC air or just air). The current furnace is extremely noisy. We can't use the den to watch TV because of the noise. I was considering going to lower cfms to cut back on the noise. I have to wonder if the ductwork is too small for 1600 cfms. But I don't want to run into issues where the top floor (3rd floor) isn't getting enough air flow.

Any further input would be much appreciated!

    Bookmark   November 27, 2011 at 12:28PM
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I strongly believe you are oversized on furnace.

My first choice on new furnace would be a two stg var speed mdl correctly sized.

My second choice would be a sgl stg model with the X-13 high eff blower motor.

Both choices will be much quieter than what you have.

Obviously if you intend to keep existing 4 ton AC which I suspect is also oversized, new furnace must have a 4 ton blower rating, minimum 1600 CFMs.


    Bookmark   November 27, 2011 at 12:56PM
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Thanks Tigerdunes, your knowledge is very appreciated. I do not have the money to replace the AC at this time. I know you are right, that it is oversized. I suspect--though I have no proof--that the developer in '91 installed whatever size he could buy in bulk at the best price for all the townhomes, even though the townhomes vary somewhat in square footage. But most importantly, I have to live with it, because I cannot afford to replace the AC, and also it's working fine (the AC doesn't get much of a workout so not as much wear and tear).

I also should have mentioned my ductwork is extremely noisy throughout the house. Again, I am sure the developer just did what was quickest/cheapest when installing the ducts, but I cannot open up all the walls of this 3-story home and improve the ductwork. Because of the ducts' noise, I do not want a variable blower that is on all the time; even at ultra low speeds, the duct noise will be intrusive. I also want to keep costs down, and a non-variable motor is less expensive.

Can you tell me why I should choose a single-stage with non-variable motor over a 2-stage with non-variable motor like the Carrier Performance 80? Do any 2-stage models come with X-13 high-eff motor you mentioned (I googled, and couldn't find any).

Also, any comments on the $480 10-year labor warranty would be appreciated. Perhaps I can talk down the price a bit, but even then, not sure it's worth it.

    Bookmark   November 27, 2011 at 6:57PM
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If noise is a factor, the choices I have recommended are worthy of consideration.

A PSC AC blower motor in a new furnace will give you similar results on noise that you are enduring now.

If price is the driving factor, I can't help you other than to ask your dealer for recommendTions to reduce noise.

You have a mistaken opinion on var speed blower motors. And I do not believe you will find an X-13 blower motor in a two stg furnace model.

Good luck

    Bookmark   November 27, 2011 at 7:14PM
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Tigerdunes - can you expand on my mistaken opinion on var speed blower motors? Please realize I am not knowledgeable about HVAC. I do know that my ductwork is very noisy. Please explain what you meant. I want to understand. Thank you!

    Bookmark   November 27, 2011 at 7:40PM
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If your warranty covered both furnace and AC then $480 would be reasonable. However for a furnace only it seems steep. A properly installed furnace should have no issues for the next 10 years. I would advise to skip the labor warranty.

    Bookmark   November 28, 2011 at 7:26AM
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Is the vent you have now a straight vertical to the roof? If so U can use it ...by installing PVC in pieces from the 1st floor or hire a roofer to drop it down the inside vent shaft...supports for the vertical pvc is easy to do...your carrier guy is a smooth talker. Get the right size unit. And live without ac till you can afford it. Get window unit temp.

    Bookmark   November 28, 2011 at 2:59PM
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Variable speed motors do not 'run all the time'.

    Bookmark   November 28, 2011 at 4:29PM
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Chuckfh - as mentioned, I am trying to keep costs down. Also, as I said, my AC is working absolutely perfectly, and I don't put large demands on it. It may be oversized, but I cannot see spending thousands of dollars to replace a working AC, or, as you said, living without it, solely because it may be oversized.

Tigerdunes has recommended twice that I buy a furnace with variable speed motor. I had understood that to help equalize temperatures in different parts of the house, variable speed motors are always blowing air. Weedmeister is saying that is not true. So both have indicated I am mistaken, but it is frustrating that neither has elaborated further. In any case, as mentioned my concern is that my ductwork is excessively noisy. If someone could explain why a variable speed motor would be the best choice for my situation, I would be very appreciative. TIA.

    Bookmark   November 29, 2011 at 8:35AM
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The variable speed motor doesn't run at the same set speed like typical fans. It is possible your ductwork is noisy because your trying to force too much air thru limited space. Your ductwork likely can't handle 4-tons of air.

    Bookmark   November 29, 2011 at 10:55AM
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A furnace with a variable speed fan could help your noise issue when it is running in a lower speed. This assumes the bulk of the noise is coming from air rushing through your duct work. You will still hear noise when the fan is running in the high speed mode.

I looked at the Product Data Manual for the Carrier Performance 80 2-stage furnace. The 110,000BTU/1600CFM size furnace has a variable speed blower. It must be variable speed since it can operate in Low and High heat stages, and cooling. The blower has 5 speed settings which can assigned to the heating and cooling stages. These speeds are set up when the furnace is installed. The challenge for your case is to set the slowest speeds so that the furnace will not run too hot, or freeze up with running the AC. The fan is set at the factory to run continuously in the low speed. I believe this can be turned off by the installer if you don't want this mode. You should discuss these points with the installer.

The general consensus is the 110,000 BTU furnace is too big for your townhouse. This will mean the furnace will run in the low stage most of the time. This will result in quieter operation. I highly recommend spending the money on a 2-stage thermostat. This will allow you you better control of the low and high heat stages.

    Bookmark   November 29, 2011 at 2:26PM
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When I refer to variable speed, I mean a blower that follows a profile whereby it starts slow (letting the furnace heat up or extracting more humidity during cooling) and ramps up to a higher speed after a few minutes. Then at shutdown, it reduces to a low speed for a few minutes (to extract residual heat or cool) and then shuts down completely.

There are other 'variable speeds' that adjust the CFM based on perceived load.

Then there are those that are 'variable speeds' that are actually set by the installer based on the BTUs of the furnace or AC. Afterwards it runs an that one speed selected, unless it is a multistage setup. Then it would run a 'low' and 'high' (whatever the installer picked for each).

    Bookmark   November 29, 2011 at 3:43PM
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Thank you Neohio, Mike and Weedmeister! That was very helpful. I have another Carrier contractor coming tomorrow. He will do a load calculation also. His company has high ratings on Angie's List, so I am hopeful he will be knowledgeable and lay out the best choices for my situation. BTW, I figure to stick with Carrier, since the 20-year-old one I have now has been great.

    Bookmark   November 30, 2011 at 9:07AM
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I had the same experience with Carrier. My furnaces and ACs lasted 25 years with a minimum number of problems. This influenced my decision to stay with Carrier.

If you have access to several good Carrier dealers in your area, then it makes sense to stick with one brand and find the best installer. It makes it a lot easier to compare the quotes from the contractors. This is the method I used and it worked well for me.

    Bookmark   November 30, 2011 at 9:33AM
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Update - I had a Bryant dealer do a load calculation. Also, he told me that I actually do NOT have a 4-ton AC, it's a 3-ton, though there is duct restriction. My current 20-year-old Carrier furnace is 110,000 btu's, and has an 048 blower capacity, which can deliver 4 tons of cooling, even though my AC is a 3-ton. As mentioned, I will not be replacing my AC which is working perfectly.

His load calculation came up with a cooling load of 33,000 btu's (just under 3 tons), and a heating load just over 70,000 btu's. As I mentioned in my OP, I can only do an 80%-efficiency furnace. So, this Bryant dealer is recommending installing a 2-stage 90,000 btu furnace (90,000 x 80% = 78,000, i.e. close to my heating load), with a 042 blower capacity (i.e. 3.5 ton blower) so that we would still have the extra "push" for the AC and we could possibly reduce some of the velocity-related noise during the summer months. Again, I do have duct restriction.

My understanding is that Bryant and Carrier furnaces are the same, though Bryant may be priced slightly cheaper.

I would appreciate any feedback on this recommended Bryant setup, and any other advice. Thank you in advance.

    Bookmark   December 5, 2011 at 3:47PM
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I am happy to hear you have found a contractor which will do a load calculation. I am going to assume he has done it correctly and will show it to you. The sizes he has calculated seem more reasonable. The 90,000 BTU furnace with the small blower should work well for you.

Is the Bryant furnace the equivalent of the Carrier Performance you were considering with the other contractor? Did you get the model number of the furnace?

Don't forget to discuss what filter you getting (4 inch is preferred), and if your old thermostat will be able to control the 2-stage furnace. If not then consider upgrading the thermostat.

    Bookmark   December 5, 2011 at 6:55PM
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Two stg var speed correctly sized!

You might want to check your math.

90 at 80% eff= 72 KBTUs

I would want a good box filter cabinet as well.


    Bookmark   December 6, 2011 at 9:06AM
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Tigerdunes - thank you so much for pointing out the math error! I simply copied the 78KBTUs from the contractor's email. Given that the correct math results in 72KBTUs, is a 90KBTU furnace enough? Perhaps the first contractor was correct that I need 110KBTUs. Keep in mind that in Chicago, nights at 5-below-zero happen frequently. And my ductwork is too narrow, and leaks like nobody's business. My windows are large and drafty.

The Bryant model number the contractor is recommending is 312AAV42090. He said that looking at the specs/blower/fan curves, that model would be a good fit, with a second choice (that he does not really recommend) being 312AAV048090 (i.e. still 90KBTU, but a bigger blower).

I am also disappointed that my existing Honeywell T8602D Chronotherm IV thermostat will not work with a 2-stage furnace (I called Honeywell to confirm). When I read the reviews on Amazon of the new Honeywell thermostats that would work with a 2-stage furnace, I am not encouraged. It almost makes me want to go with a single-stage furnace, just so I can keep my great thermostat.

Any advice on the BTU's, or anything else would be appreciated!

    Bookmark   December 7, 2011 at 8:49AM
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The 90 should be fine.

What design temps did your dealer use for heating-inside temp and outside temp. This makes a difference. On heating, I always use the winter low average temp and then subtract 10 degrees for those rare extreme temps. I would be interested in knowing what your dealer used.

I would not purchase a two stg furnace that did not have a var speed blower. I will check the mdl dealer has quoted. It is important to have a true two stg thermostat for a two stg furnace.

You are going to have ductwork checked for leaks and sealed?

What are you doing about a filter cabinet?


    Bookmark   December 7, 2011 at 9:16AM
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Please do not select a furnace so you can you use your old thermostat. I am confident you will adopt to a new 2-stage thermostat.

I found the product data sheet for the Bryant 312AAV series furnace. It appears to be the equivalent to the Carrier Performance 2-stage furnace. The 312AAV090 version has an input rating of 88,000 BTU with an output rating of 71,000 BTU. Make sure the contractor has done the load calculation correctly and verify the indoor and outdoor design temperatures.

This is a variable speed furnace in that the blower can operate at 4 speeds. The contractor will choose two speeds for the high and low heat stages, and one speed for the AC.

    Bookmark   December 7, 2011 at 12:24PM
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I don't mean to be disagreeable but the statement above is not accurate.

While the 312AAV is two stage, it s not var speed. It has a PSC motor fixed speed with separate settings. It is not an energy efficient motor compared to a DC var speed blower motor. I would not have it for my home nor would I recommend this furnace.

Your options for var speed are as follows:

1. Look at Carrier Infinity 80 or Bryant Evolution 80. They are identical. I
This furnace does require their proprietary Evolution controller.

2. Other option is to look at Trane or AmStd XV80 furnace which is var speed and can take a HW two stage thermostat

3. Another option is Lennox SL280V which is also 80% eff two stage and var speed. Same size is available from Lennox as the Bryant furnace.


    Bookmark   December 7, 2011 at 1:16PM
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Perhaps the term "variable speed" is not correct to describe this Carrier Performance or equivalent Bryant furnaces. The Bryant brochure describes it as a "multi-speed" furnace. It is a big improvement over the single stage furnace.

No arguement the Carrier Infinity or Bryant Evolution furnace with the DC motor is much more attractive. However it is significantly more money. I thought the OP was trying to keep the costs down, but if the funds are available then go for it.

Both of these furnaces have a 1/2 HP motor. I can't tell which is more efficient, but lets say for argument's sake the DC motor is 25% more efficient. How much electricity is saved during a typical heating season?

In my opinion there is nothing wrong with this furnace. There are better furnaces if you want to spend additional money.

    Bookmark   December 7, 2011 at 7:22PM
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Thank you Tigerdunes and Mike_home. Mike is right that I am trying to keep costs down. And a 2-stage 90KBTU new furnace will still be an improvement over what I have now.

In answer to Tigerdunes' question about design temps - the contractor said it is based on maintaining 70 degrees at an outdoor temperature of 5 below zero.

The contractor mentioned sealing the ducts by shooting something through them. He said it would offgas a smell like paint for about 20 minutes, which did not appeal to me. I don't want to be breathing a chemical spreading throughout my house. But perhaps I need more information. Can you give me a little insight into the sealing process? Is this a worthwhile option?

A filter cabinet - the furnace is located in a small closet off a den. There is barely space for the furnace. I've been changing the filter for 7 years by bending down into that tiny space, and it's not a big deal - it takes me about 3 minutes. I will ask the contractor anyway, to see if there is any way we can fit a filter cabinet.

The contractor mentioned with enthusiasm the Honeywell touchscreen thermostat (I believe, but am not certain, it is the Pro 8000, or in the 8000 series). He also mentioned the 9000, which he thought would be overkill for me. When I said I had seen some negative reviews on Amazon of touchscreen Honeywells, he said those are the DIY's you can buy on Amazon or at Home Depot, but the pro-versions won't have any problems. Do you agree/disagree?

    Bookmark   December 7, 2011 at 10:41PM
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I did a quick look at some of the reviews on Honeywell touch screen thermostats on Amazon. In general the reviews are very positive. Some of the very negative reviews were from people who were trying to do an installation with a heat pump or a 2 stage furnace. There were also complaints about poor customer service and confusing installation instructions. Some people had thermostats which were defective right out of the box.

The commercial version of the Honeywell thermostat is covered by a 5 year warranty when installed by a qualified technican. Your contractor will be responsible for proper installation. The contractor seems to have experience with this thermostat.

Please keep us updated on the installation and your thoughts about the furnace.

    Bookmark   December 8, 2011 at 8:56AM
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Final thought and I will leave this thread.

If you plan on staying in this townhouse for the foreseeable future, then not getting a var speed model is a big mistake.

The longstanding axiom applies.
Comfort, satisfaction, quality are long remembered over price.

You do want a two stage thermostat for a two stage furnace where the stat controls the staging over the timer on a control board. Big difference on best operation of furnace, comfort, and operational savings.


    Bookmark   December 8, 2011 at 9:29AM
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The honeywell 8000 series tstats are just fine. ITs the one i have on my wall at home, been there 6 years and we install them all the time for customers. NO problems there.

On another note. I would recommend a variable speed furnace if you can afford it.... opens you up to 2 stage cooling if you want it when you do replace your a/c later. just a thought.

    Bookmark   December 8, 2011 at 11:19AM
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