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I just bought a new townhouse, and the furnace needs to be replaced.
The townhouse was built in 1977, and the furnace is original to the unit. It has cracks on both sides of the heat exchanger, and needs to be swapped out.
I've had three estimates, and they've all said different things, and I'm not sure exactly what to do.
The furnace is 110,000 BTUs, which they all agreed was too much for my townhouse space (1500 sq ft on two floors, plus a basement). There is also a 14 year old hot water heater that is 40,000 BTUs. Both vent into a chimney.
Estimate #1: Suggested replacing with an 80,000 BTU 80% modular furnace made by York. Modular furnaces, he said, have better comfort level and save on energy. He also said that I need to put in a new flue liner in the chimney. He never checked the existing flue liner in the chimney, nor asked about replacing the thermostat. Cost: $5,800
Estimate #2: Suggested replacing with an 80,000 BTU 80% two-stage furnace made by York. He said that the 80% modular furnaces are new and prone to problems, and he doesn't plan to sell them for at least a few years until they get the kinks worked out. He said I would not need to replace the chimney flue liner, and explained the difference between three levels of Honeywell thermostat (the middle grade is included in price). Cost: $3,000
Estimate #3: Suggested replacing with a 90,000 BTU 80% two-stage furnace made by Carrier. He said this comes with a "safe chimeny adapter" which would mean I wouldn't need a flue liner - though he said I would need a flue liner if I bought a York without the adapter. He said that all details on the adapter were available at the Carrier website, but they are not - and it looks like it's more to protect the furnace than to protect the chimney. He includes the lowest grade Honeywell thermostat. Cost: $3,500
So, three estimates, three different opinions, and I'm as much in the dark as before. I'm going to continue to get opinions before deciding, but was hoping there were some HVAC experts on hatrack that might be able to chime in.
Posts: 3960 | Registered: Jul 2001
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They save on energy because they are never running at 100% capacity.
Standard furnaces are either on or off, 100% or 0%. So, if the thermostate is set at 67 degrees, and it senses the house is at 65 degrees, it will come on full-bore until the thermostat hits 67.
Two-stage furances have two "on" levels, one at around 60% and the other at 100%. It first kicks on at 60% for 15 minutes, and if it doesn't reach the target level, it jumps to 100%.
Modular furnaces have multiple levels. They first kick on at 50%, then increase gradually 1% at a time until they hit the target level. So, if after 15 minutes the target hasn't been reached, they go to 51% for a time, then 52%, etc, until the target is hit. In that way, they are almost never running at 100% capacity, and thus save on energy.
So, modular would definitely save the most, but it is new technology for 80% efficiency furnaces and may be prone to version 1.0 problems. They are also the most expensive. Standard are the least energy efficient and cheapest.
Posts: 3960 | Registered: Jul 2001
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We had to have our furnace replaced three months ago. When Michigan Consumers Power sent out someone to check our furnace and see why it would not turn on, he discovered a crack in the heat exchanger and said he was required by law to shut down the furnace and tag it as not being usable. This information was also forwarded to the local government regulatory agency, who sent us a note asking if we had replaced the furnace or had it repaired yet. (The contractor who installed our new furnace gave us the signed postal reply card for us to send in required to satisfy the government.)
A crack in the heat exchanger is serious, because it can let carbon monoxide into the living space, and kill everyone. We were fortunate, actually, that the furnace stopped working, so we had to get it checked. I did notice an odd, kind of scorched smell the last few times the furnace was on, before it quit.
Anyway, let me suggest you get someone to give you a quote on replacing your furnace with a Rheem. They are not advertised as much as Carrier or York, but seem to be as highly regarded, relying more on word-of-mouth.
Our local contractor advised us that the Rheem furnaces tend to be a little noisier, which could matter if you do not have a basement to put it in. We don't have a basement, the furnace is in the utility room with the washing machine and hot water heater (sharing the chimney with the hot water heater) and dryer. So he recommended the quietest Rheem model, which is a "Rheem Classic Series Super Quiet 80." The 80 of course means it has an 80% efficiency rating. (Our 25-year old Lennox furnace was not rated, but contractors estimated it was probably about 60%.)
It is still a little noisy, but the moderate rushing sound is easy to ignore, not a bother to us at all. We are just glad to have heat!--and have it reaching the furthest bedrooms in the house. And the new digital thermostat keeps the temperature in the living room within a quarter of a degree of where it is set. So we set it at 72 and the ambient temperature stays at 72.
We had another quote earlier from a contractor that dealt with Carrier, and the comparable Carrier cost about $500 more than the Rheem, according to the estimate we were given. Our Rheem cost about $2800 fully installed. That included having the contractors remove and dispose of the old furnace, and do the sheet metal work needed to make the furnace fit the existing ducts (the Rheem was only about 2/3 the size of our old Lennox). Both were figured based on the square footage of our house, so they were the same capacity. We have a fairly large, four-bedroom house with a 20' by 20' living room.
The Carrier and the Rheem both were also available with units that had 90% efficiency ratings, but they cost many hundreds of dollars more. Since we had been getting by with a 60% efficient furnace for all that time, we figured a one-third improvement to 80% was good enough.
[ November 28, 2008, 04:42 PM: Message edited by: Ron Lambert ]
Posts: 3742 | Registered: Dec 2001
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quote:Originally posted by FlyingCow: They save on energy because they are never running at 100% capacity.
Standard furnaces are either on or off, 100% or 0%. So, if the thermostate is set at 67 degrees, and it senses the house is at 65 degrees, it will come on full-bore until the thermostat hits 67.
Two-stage furances have two "on" levels, one at around 60% and the other at 100%. It first kicks on at 60% for 15 minutes, and if it doesn't reach the target level, it jumps to 100%.
Modular furnaces have multiple levels. They first kick on at 50%, then increase gradually 1% at a time until they hit the target level. So, if after 15 minutes the target hasn't been reached, they go to 51% for a time, then 52%, etc, until the target is hit. In that way, they are almost never running at 100% capacity, and thus save on energy.
So, modular would definitely save the most, but it is new technology for 80% efficiency furnaces and may be prone to version 1.0 problems. They are also the most expensive. Standard are the least energy efficient and cheapest.
How does this save energy? It sounds like it would just take longer to heat up the house.
If it saves energy why doesn't it have a higher efficiency rating?
Posts: 4287 | Registered: Mar 2005
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quote:How does this save energy? It sounds like it would just take longer to heat up the house.
If it saves energy why doesn't it have a higher efficiency rating?
Modern furnace/boilers should have at least an 84% afue efficiency. By law the afue must exceed 80%. Natural gas furnaces can easily exceed 90% afue by condensing the water out of the flue gas. In that case, you don't use a chimney, you use a plastic vent, because plastic won't be corroded by the condensate.
For maximum efficiency, the furnace should run as close as possible to 100% duty cycle. Every time it shuts down, the heat remaining in the furnace goes up the flue. So if you turn down the firing rate, it runs longer, and shuts down less often, which saves energy. Also, shutting down allows condensation to form and starting up generally creates soot. So preventing short cycles increases the life of the furnace.
FlyingCow: What kind of fuel you are using? Also, you are using the term "furnace." I assume you mean forced hot air. Yes?
I'm assuming the flue lining he's suggesting has to do with flue diameter to correctly match the flow rate from the furnace. Old flues were invariably sized larger than needed. Same with furnaces. They used to oversize them so you'd have "plenty of heat," except that every time they short cycled, you would go through a period of cold before the furnace kicked back on. That's what he means by "better comfort level."
The three estimates you got don't seem inconsistent to me. The first guy is obviously placing trust in a new technology that is based on sound science, but as it has been pointed out, may need the kinks worked out. I don't know enough about these furnaces to tell you how reliable they are, but the two stage furnace is going to be WAY more efficient than an old single firing rate burner. The modular furnace just carries the same paradigm to a greater extreme.
Since it's clear that since the modular furnace is significantly more expensive, I would tend to stay with more proven technology. I am concerned about the sizing difference between the 2nd and 3rd estimate. It's pretty important to get that size right. The 3rd estimate could be stuck in the old "give you a nice big furnace so you'll have plenty of heat" mentality, but I don't know.
Posts: 3735 | Registered: Mar 2002
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The furnace would be natural gas, and it is forced air.
The first estimate (public service) had talked a bit about the size of the flue with regard to the flue liner. He said between the furnace and hot water heater, I had been pushing 150,000 BTUs... and with the new furnace, that would drop to 120,000 BTUs, which would mean the current flue is too big. (I am also thinking of replacing the 14-year-old water heater, perhaps with an on-demand model... not sure how this affects the numbers, and didn't think to ask)
He never actually looked at the flue to see what size it was, though. He suggested bringing it down to 5" x 5", and assumed it was a 7" x 7".
Is there anywhere I can read up on this to know for sure? Three "experts" all had different opinions on the matter.
What I didn't like about him was that he really seemed like he was pushing for a big sale. Modular furnace (didn't even quote standard or 2-stage) and pushing hard for a flue liner without even looking at the existing one.
As for the cracks in the exchanger, the inspector said they were hairline and not yet serious, but that I should definitely look into replacing it sooner than later.
As for the sizing difference for the third estimate, he said that Carrier doesn't make an 80,000 BTU furnace - that they have a 70,000 and a 90,000 and the 70,000 would be too small.
Posts: 3960 | Registered: Jul 2001
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quote:It sounds like it would just take longer to heat up the house.
From what the three guys were saying, I'd very rarely ever need 100% burn to heat the house, especially in a townhouse. They are designed to heat a house from 0 degrees farenheit with four cold walls. The unit has only two cold exterior walls, and it is only very rarely that weather in NJ drops down to 0 or below.
It can pretty much run at 60% and heat the house without any difficulty.
Posts: 3960 | Registered: Jul 2001
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quote: I am concerned about the sizing difference between the 2nd and 3rd estimate. It's pretty important to get that size right. The 3rd estimate could be stuck in the old "give you a nice big furnace so you'll have plenty of heat" mentality, but I don't know.
Carrier doesn't make 80,000 BTU furnaces. They have 70,000 and 90,000. I had the 90,000 BTU carrier installed last year. Salesman recommended the 70,000 one first but when I asked why all the other contractors said 80,000, he changed it to the 90,000 one (and didn't mention that they didn't make 80,000 BTU ones ). In retrospect, I suspect the 70,000 one would have been enough for my 1650 sq ft townhouse.
About the thermostats, check and see how many wires you have running from the furnace to the current thermostat. If possible, you may want to run extra wires to get a more advanced thermostat. There are thermostats which allow you to control when the heat goes on high but they need more than 4 wires. With a standard 4 wire thermostat, it would be as what you've been told, 15 minutes at low then it automatically goes to high.
Posts: 176 | Registered: Aug 1999
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quote:...Carrier...adapter...looks like it's more to protect the furnace than to protect the chimney.
...the flue lining...has to do with flue diameter to correctly match the flow rate from the furnace.
Similarly, the adapter should have been designed to ensure the proper draft so that the furnace can run at optimum efficiency and safety during operation.
quote:As for the sizing difference for the third estimate, he said that Carrier doesn't make an 80,000 BTU furnace - that they have a 70,000 and a 90,000 and the 70,000 would be too small.
Ah, that makes sense. Sounds like you probably want the York two-stage, of the three mentioned, if not only for price, but because it's properly sized. As to the flue liner, you might want to ask for specifications on flue requirements. They ought to have documentation on this. It may be that the furnace outlet is sized to provide the correct backpressure so flue size is irrelevent. It sounds like that's what the "safe chimney adapter" does.
I'm curious though, that nobody mentioned condensing furnaces. They are far more efficient, they've been around since the '80s so they're pretty well established technology, and they vent through a plastic pipe in the wall, so flue size is irrelevent.
Posts: 3735 | Registered: Mar 2002
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They mentioned that townhouses generally are not allowed to have furnaces that vent through a PVC pipe through the wall, because there are regulations about proximity of this pipe to other units/windows/etc. If I were on an end unit, it might have been possible, so they said.
I'm going to call Carrier on Monday to see exactly what this "safe chimney adapter" does. My biggest concern at this point is whether I have to drop $1500 on a flue liner or not. I'm pretty much decided on getting an 80% two-stage.
Posts: 3960 | Registered: Jul 2001
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So, I called Carrier today, and they had no idea what I was talking about when I mentioned a "safe chimney adapter". They couldn't figure out what the HVAC was trying to describe, and said that it wasn't anything they manufactured.
So... yeah.
I'm starting to think the guy just didn't want to go through the trouble of putting in a chimney flue liner - though he sold the same thing to my neighbors on both sides. Curious.
I'm going to have a few more estimates come in and ask each about the flue liner. I wish there were more online about it.
Posts: 3960 | Registered: Jul 2001
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Is there a Trane representative in the area? Or have they merged with someone else?
We felt the Trane reps were the most professional, and they came in at the midpoint as far as estimates went.
Here's the other thing: If your furnace is that old, (ours was about the same vintage) even if you get a mostly *inefficient* furnace by today's standards, you are still going to be saving hundreds, if not thousands of dollars on natural gas, compared to the old one, because the old ones were that horribly inefficient.
--We have a single family detached house in the Chicago area. It is horribly insulated so there is lots of heat loss (we are working on improving that as we go) Our first winter's heating bills were up to $250/month. With the new furnace they are down to about $80/month.
Posts: 11265 | Registered: Mar 2002
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Also, since these contractors you are dealing with seem all over the map. I'd ask each how they handle your town's safety inspection and/or installation permits. Make sure they are responsible and aren't going to charge you extra for additional labor if it doesn't pass the first time.
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). In retrospect, I suspect the 70,000 one would have been enough for my 1650 sq ft townhouse.
