New Furnace question.

[Danh]

Just had a new furnace installed that came with a surprise. It seems that at least high-efficiency furnaces and perhaps all, have a very hearty appetite for cold air intake. Older homes, even those built in the 80s, don’t have cold air ductwork that match those requirements. The result is blower motors working really hard to inhale cold air, noise, and perhaps shorter blower life.

So, if you’re getting a new furnace, measure the square inches of your cold air returns and make sure they are comparable to those of the heat ducts. If not, question your HVAC contractor about the consequences. In addition, make sure your air filter fitting is of sufficient size for the new furnace.

I fell afoul of both these problems and had to install a new cold air return and a new air filter box. I’ve had a long relationship with my contractor and they have been terrific but are trying to adjust to what seems to be suddenly introduced technology across all brands. I’ve spoken with one other homeowner who randomly brought up the same problem with a different producer.

 

[thastinger]

So...an 80% efficient heating system with a cooling coil and external compressor of about 3.5-4.5 tons should cost about what installed? Name brand.

I don't think you can even buy an 80% furnace anymore, I know you can't buy a heat pump that is less than 15 SEER

 

[Nukeman7]

I don't think you can even buy an 80% furnace anymore, I know you can't buy a heat pump that is less than 15 SEER

Trane and other companies have several models of 80% efficiency gas furnaces available. EPA/DOE has been suggesting a proposal to mandate 90%+ furnace efficiency beginning in 2029, but it has not gained traction so far.

 

[nickaluch]

Just had a new furnace installed that came with a surprise. It seems that at least high-efficiency furnaces and perhaps all, have a very hearty appetite for cold air intake. Older homes, even those built in the 80s, don’t have cold air ductwork that match those requirements. The result is blower motors working really hard to inhale cold air, noise, and perhaps shorter blower life.

So, if you’re getting a new furnace, measure the square inches of your cold air returns and make sure they are comparable to those of the heat ducts. If not, question your HVAC contractor about the consequences. In addition, make sure your air filter fitting is of sufficient size for the new furnace.

I fell afoul of both these problems and had to install a new cold air return and a new air filter box. I’ve had a long relationship with my contractor and they have been terrific but are trying to adjust to what seems to be suddenly introduced technology across all brands. I’ve spoken with one other homeowner who randomly brought up the same problem with a different producer.

Yes when I had a new system installed I went with bigger duct work for the supply and returns. The old duct work very high quality but just not big enough to move the air. With that I added a few new supplies while I had everything open to help balance the comfort

 

[PandaBear]

I don't think you can even buy an 80% furnace anymore, I know you can't buy a heat pump that is less than 15 SEER

In some climate you still can. A lot of people buy them because they don't want to redo the exhaust / vent work for condensation of the higher efficiency furnace and they don't use that much heat.

I have a <80% one installed in 94 and it is probably used only 40 days a year a couple hours each time right before sleep. I would just keep replacing draft fans until the heat exchanger is burnt through.

 

[I<3oil]

I don't think you can even buy an 80% furnace anymore, I know you can't buy a heat pump that is less than 15 SEER

We just had an all new furnace and new outside AC unit put in a year ago Oct.....it was $6700 all in. We had quotes from $5600 up to $9800. 80% furnace (110k btu) and a 13 SEER AC unit.

 

[tbm5690]

Time for a new furnace. Are there any pros/cons to a one stage versus a two stage furnace? Is Bryant a decent brand? Is 96% efficiency good for a modern furnace? I seem to recall going for super high efficiency had some downsides, perhaps longevity. TIA.

You're not as cold as me, but after having a 2 stage I don't think I'd ever go back. 2 stages don't have increased issues from what I've seen...it's the modulating furnaces that come with higher maintenance cost typically. 96% is good yes...the highest I've seen is 97%. 2 stage means more comfort...mine barely uses stage 2 unless it's ramping up to a higher temp. The BTU rating on the furnace will be the stage 2 output...in my case it's a 60K BTU furnace but about 48K BTU for stage 1 heat.

 

[Nukeman7]

Secondly I think Bryant is on the low end but not bad. Most companies own "three different brands " i.e. high medium and low end. Make sure whatever you buy make sure it has access panels for easy repairs. Third don't under any circumstances purchase a heil brand. My friend works for his cousin in hvac and apparently Heil won't sell you parts just a number of a repair company.

Bryant is owned by Carrier and is mid-tier. Heil is Carrier's lower-grade brand, but most of the internals are interchangeable. Officially, most of the major brands other than Goodman won't sell parts to the public, but there are dozens of HVAC online parts stores that will sell nearly any part to the residential customer. I have sourced various proprietary parts for Trane, Lennox and Carrier from Amazon and SupplyHouse.com. Goodman uses many generic off the shelf parts available locally.

Here is a list of the major manufacturers and the brands in their family:

• Carrier Corporation owns Carrier, Bryant, Arcoaire, Comfortmaker, Day & Night, Heil, Payne, and Tempstar.
• Trane Technologies owns American Standard, Trane , Oxbox, and RunTru.
• York owns York, Coleman, and Luxaire.
• Rheem Manufacturing owns Rheem and Ruud.
• Daikin owns Goodman, Amana, and Daikin.
• Nortek Global owns Maytag, Frigidaire and Broan.
• Lennox owns Lennox, Ducane and Armstrong.

 

[hrv]

I don't think you can even buy an 80% furnace anymore, I know you can't buy a heat pump that is less than 15 SEER

You sure can there are many 80% gas furnaces on the market by just about every company....

 

[slug_bug]

Thanks for all of the great info and advice everyone!

 

[RhondaHonda]

There’s a new refrigerant coming in equipment manufactured after 2024 so if you are also considering replacing the AC, that’s something to keep in mind so you aren’t the guinea pig.

I would think a variable speed fan in a 2-stage furnace would be ideal. Nothing too fancy or expensive to repair but better comfort and less noise. That’s what I’ll likely go with when the time comes.

 

[HowAboutThis]

Time for a new furnace. Are there any pros/cons to a one stage versus a two stage furnace? Is Bryant a decent brand? Is 96% efficiency good for a modern furnace? I seem to recall going for super high efficiency had some downsides, perhaps longevity. TIA.

When I lived in the Upper Midwest I had a variable speed type thing. One of the super duper efficient ones. I just remember the house always felt warm because it would basically always be blowing a little bit of warm air doggone near continuously. Rarely shut off, but had a way to reduce natural gas volume and fan speed and such. I liked it. Over 5 years don't recall ever having an issue with it. House was also super energy efficient and some 3rd party rated 5-star energy efficient or something along those lines. Had insulated concrete foundation for the basement, blown in foam around everything near outside walls, blown insulation in the attic, etc. Thing was air tight and had an air exchanger to help the place breathe LOL. It was great!

With that said, if your house isn't as energy efficient I can't tell you what you'll get from more than a 1-stage. I currently have a 1-stage, 80% efficient, that I posted about having way too many cycles per hour. I think it's oversized. Bought the house, wasn't here for the furnace install. If you're upgrading from, say, an 80% or 90% to a 96% efficient, I believe those numbers tell you how much energy gets pushed to your house vs. how much gets shot out the chimney (if it's gas) or wherever else (if it's electric). But you're making a ton of assumptions---is your duct work in good shape? Have air gaps and leak a lot? How leaky is your house? Etc. So there are a ton of variables to think about while you're buying. If you get a 60K BTU 80%, you're essentially going to get 48K BTU's to your house (assuming the ductwork doesn't lose a bunch of energy). If you get a 60K BTU 96%, you're essentially going to get 58K BTU's to your house. So some things to keep in mind are if you're replacing an 80% with a 96%, you may not want to just swap a 60K BTU for another 60K BTU because you could potentially end up "oversized", given the increase in efficiency and BTU's making into your home. A REALLY good contractor will do calculations and have an idea. I'm pretty confident whoever installed in the house we moved into just slapped in a furnace without using their brain. Because I've had to adjust the CPH to get longer, and supposedly more efficient, burner run times. I'd venture our furnace is close to twice the BTU's it needs to be.

Anyway, I'd get multiple quotes, ask multiple places, hear what they have to say, research online (although I've found some of those people that claim to know things don't know as much as they claim). In, hopefully 10 more years, when this furnace needs replacing I'll be pretty anal about choosing a contractor that puts some thought into things, even if it costs more.

One thing you might want to think about is the efficiency of your current furnace and on "average" winter days time a few cycles when you have the temp set constant to see how long from the time the furnace starts until the time it starts again and how long the furnace actually runs in the time period. Then, if you know you have a say, 80% efficient 50K BTU, you could at least have a very rough estimate of the BTU's you'd need in a 96%.

 

[Nukeman7]

So there are a ton of variables to think about while you're buying. If you get a 60K BTU 80%, you're essentially going to get 48K BTU's to your house (assuming the ductwork doesn't lose a bunch of energy). If you get a 60K BTU 96%, you're essentially going to get 58K BTU's to your house. So some things to keep in mind are if you're replacing an 80% with a 96%, you may not want to just swap a 60K BTU for another 60K BTU because you could potentially end up "oversized", given the increase in efficiency and BTU's making into your home. A REALLY good contractor will do calculations and have an idea. I'm pretty confident whoever installed in the house we moved into just slapped in a furnace without using their brain. Because I've had to adjust the CPH to get longer, and supposedly more efficient, burner run times. I'd venture our furnace is close to twice the BTU's it needs to be...

One thing you might want to think about is the efficiency of your current furnace and on "average" winter days time a few cycles when you have the temp set constant to see how long from the time the furnace starts until the time it starts again and how long the furnace actually runs in the time period. Then, if you know you have a say, 80% efficient 50K BTU, you could at least have a very rough estimate of the BTU's you'd need in a 96%.

Don't take this the wrong way, but the statements highlighted above are fundamentally incorrect. A 60K BTU furnace will deliver the same amount of thermal energy to your home, regardless of whether it is rated at 80% or 96% efficiency. However, the 80% efficient furnace will consume more natural gas/propane to generate 60K BTUs. The furnace's fuel efficiency rating value has no bearing on the heat loss between the air handler and the discharge vent ducts inside the home. That is contingent upon the size, layout and condition of the conditioned air supply ductwork/insulation.

Once the HVAC contractor performs a Manual J calculation based upon the specific heating/cooling needs of your house, the proper size furnace and A/C unit can be determined. If the evaluation concludes that a 60K BTU furnace is the correct size, it won't be undersized/oversized whether you purchase an 80% or 96% efficient model. Likewise, if you need a 3 Ton A/C unit, selecting a 19 SEER unit wont make it oversized compared to a 15 SEER unit. It will just take less electricity for the 19 SEER A/C system to deliver the same degree of cooling as the 15 SEER unit.

However, it is true that some premium features such as multiple stage burners, variable speed scroll compressors and variable speed blower fans can affect the run times and how much the interior temperature fluctuates between the on/off cycles, thereby influencing the perceived level of comfort.

 

[greenjp]

Once the HVAC contractor performs a Manual J calculation based upon the specific heating/cooling needs of your house, the proper size furnace and A/C unit can be determined.

This is the real trick, isn't it? How many companies actually will do this vs. just look at what you already have and offer the same? In my experience it was "none" and this seems to be the norm.

2 stage furnace sorta helps wrt oversizing, we had one in our last home and as someone else noted it always ran in the first stage aside from when making up a large temperature difference.

In our new home we have two systems, one of which is the original from 2000. I have been gathering data on how the AC and heat operate at different outside temperatures and have determined that the downstairs 3 ton AC is massively oversized, both in terms of the run time on the hottest days and airflow requirement compared to the duct sizing. I'll be telling whoever we hire to replace it to go down to 2 tons, curious to see what sort of response I get to that.

jeff

 

[RhondaHonda]

Don't take this the wrong way, but the statements highlighted above are fundamentally incorrect. A 60K BTU furnace will deliver the same amount of thermal energy to your home, regardless of whether it is rated at 80% or 96% efficiency. However, the 80% efficient furnace will consume more natural gas/propane to generate 60K BTUs. The furnace's fuel efficiency rating value has no bearing on the heat loss between the air handler and the discharge vent ducts inside the home. That is contingent upon the size, layout and condition of the conditioned air supply ductwork/insulation.

Once the HVAC contractor performs a Manual J calculation based upon the specific heating/cooling needs of your house, the proper size furnace and A/C unit can be determined. If the evaluation concludes that a 60K BTU furnace is the correct size, it won't be undersized/oversized whether you purchase an 80% or 96% efficient model. Likewise, if you need a 3 Ton A/C unit, selecting a 19 SEER unit wont make it oversized compared to a 15 SEER unit. It will just take less electricity for the 19 SEER A/C system to deliver the same degree of cooling as the 15 SEER unit.

However, it is true that some premium features such as multiple stage burners, variable speed scroll compressors and variable speed blower fans can affect the run times and how much the interior temperature fluctuates between the on/off cycles, thereby influencing the perceived level of comfort.

I thought a gas furnace was measured as the input. 80k but at 90% efficiency yields 72k into the house. 80k btu at 80% efficiency is 64k into the house. Oil furnaces are output but I think gas are referring to the input.

 

[facility1]

Heil,Tempstar,Arco-air all the same furnaces,by a division of Carrier,,,all decent stuff ,the carrier brand is seperate line of furnace,,personally i have trane in my house which works fine,,can get parts at most local hvac parts houses,,,however Lenox has mostly specialized parts and only can (in most cases) need to go to a Lenox dealer and pay maximum prices,,Reem&Rudd have a nice set up,mostly builders use them ,i would avoid Goodman hvac stuff though. in all cases go through a reputable hvac contractor and look at rebates..

 

[hrv]

Just had a new furnace installed that came with a surprise. It seems that at least high-efficiency furnaces and perhaps all, have a very hearty appetite for cold air intake. Older homes, even those built in the 80s, don’t have cold air ductwork that match those requirements. The result is blower motors working really hard to inhale cold air, noise, and perhaps shorter blower life.

So, if you’re getting a new furnace, measure the square inches of your cold air returns and make sure they are comparable to those of the heat ducts. If not, question your HVAC contractor about the consequences. In addition, make sure your air filter fitting is of sufficient size for the new furnace.

I fell afoul of both these problems and had to install a new cold air return and a new air filter box. I’ve had a long relationship with my contractor and they have been terrific but are trying to adjust to what seems to be suddenly introduced technology across all brands. I’ve spoken with one other homeowner who randomly brought up the same problem with a different producer.

I have found the blower motor on my single stage carrier is much stronger then the old Goodman that was installed in 1998...You get a little more noise with the newer ones...esp the single stage over the slower older furnances...

 

[oil pan 4]

Single stage will be easier and cheaper to repair. The efficiency gained by a two stage will be more then wiped out on your first repair.

Agreed .
Yeah a single speed one could use a pretty typical motor, more likely for generic replacement parts.
For a 2 stage it's much more likely when the fan goes out that you have to have an OEM fan motor.

 

[oil pan 4]

Heat Pump?

 

[Touring5]

You're not as cold as me, but after having a 2 stage I don't think I'd ever go back. 2 stages don't have increased issues from what I've seen...it's the modulating furnaces that come with higher maintenance cost typically. 96% is good yes...the highest I've seen is 97%. 2 stage means more comfort...mine barely uses stage 2 unless it's ramping up to a higher temp. The BTU rating on the furnace will be the stage 2 output...in my case it's a 60K BTU furnace but about 48K BTU for stage 1 heat.

All true. A big benefit of 2-stage is reduced blower noise, since it runs on low heat most of the time.

Any increased repair costs are really only down to 3 parts: inducer motor, blower motor and pressure switch (uses 2 switches instead of just one). The difference in motors depends on whether they're simply multi-tap or ECM.