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SEER rating (seasonal energy efficiency rating) has nothing to do with ductwork. Those ratings are developed in a lab and measure equipment efficiencies only, directly at the equipment inlet and outlet. Ductwork does impact SYSTEM efficiency.
Let's say the system is 100k/80% eff heating for example, the old ducts in the attic leak 25% as described by the DOE, and the winter outdoor design temperature is 30°. The furnace leaks 25% of it's 130° air to the attic and the replacement air drawn from the outside is 30.
100k at 80% efficiency and you're now down to 80,000 btus at the furnace outlet....20,000 lost up the flue. 1500 cfm x .25 is 375 cfm air lost at 130 and replaced at 30...that works out to 40,687 btus lost thru leaks.
You're still paying for 100,000 btus but delivering 39,000 to the house. It only gets worse in the air conditioning mode. Tight ductwork trumps higher efficiency equipment on older system all the time.
New equipment doesn't tolerate undersized ductwork like past equipment. It impacts the efficiency and is hard on the equipment requiring more repairs more frequently and an early retirement of the equipment.
SEER rating (seasonal energy efficiency rating) has nothing to do with ductwork. Those ratings are developed in a lab and measure equipment efficiencies only, directly at the equipment inlet and outlet. Ductwork does impact SYSTEM efficiency.
Let's say the system is 100k/80% eff heating for example, the old ducts in the attic leak 25% as described by the DOE, and the winter outdoor design temperature is 30°. The furnace leaks 25% of it's 130° air to the attic and the replacement air drawn from the outside is 30.
100k at 80% efficiency and you're now down to 80,000 btus at the furnace outlet....20,000 lost up the flue. 1500 cfm x .25 is 375 cfm air lost at 130 and replaced at 30...that works out to 40,687 btus lost thru leaks.
You're still paying for 100,000 btus but delivering 39,000 to the house. It only gets worse in the air conditioning mode. Tight ductwork trumps higher efficiency equipment on older system all the time.
New equipment doesn't tolerate undersized ductwork like past equipment. It impacts the efficiency and is hard on the equipment requiring more repairs more frequently and an early retirement of the equipment.
In other words, make sure your ductwork matches the SEER rating of your A/C!
Interesting comment on the flex duct. Can you expand on it a little bit? In my attic where the handler is located, I have likely flex duct from the handler to all of the air vents in the ceilings for the floor below. They're insulated tubing hanging from straps attached to the rafters. Done when house was built in 2000. Are you saying that I should expect to replace those soon? What makes them fail?
Thanks!
The inner part is plastic, and after many years in a hot attic it will get brittle and start to tear, especially where there’s sharp turns.
1. Your ductwork is old and inefficient and "leaks like a sieve." I'm no expert, but I've inspected the ductwork in the attic and I didn't find any leaks, so I don't know where that comes from.
2. New systems push more air at lower velocities and require larger ductwork to do so, otherwise it strains the air handler fan.
3. The temperature difference between the air produce by a higher SEER system and the attic air might be greater than the insulated ducts can handle and this will cause condensation which will drip.
The upstairs is approximately 1000 sq ft. My first quote is for about $5000 just for the ductwork. I'm sort of scratching my head trying to figure out how that works. The three big items mentioned are the ductwork, the condenser and the air handler. The total quote was upwards of $15k. I'm sort of baffled that this could cost $15k. I know it isn't apples to apples, but the downstairs unit (albeit, it is an all-in-one; there's no separate air handler) was $3500 and is more tonnage than the upstairs unit. So, this quote is pretty much saying that the material and labor is $5000 for ducts, $5000 for air handler and $5000 for condenser?
It simply seems astronomical. I'm getting a second (and likely third) quote. That just doesn't seem right. I'm not looking for the highest end system. Something like a 15-16 SEER. No idea why the quote is that high.
The average older house has at least 15% duct leakage unless someone has gone to the trouble of sealing the ducts. Every single seam and connection needs mastic or tape. If they're not sealed with mastic or tape, they're leaking. Full stop, they are leaking. Might not be "a lot" of air individually, but it adds up quickly.
Where the "boots" for your registers pass from unconditioned space to conditioned space (attic or basement) needs to be caulked or taped, or you're leaking air. If you actually see air movement, you're probably losing more than 15% of your air. You can find leaks with a smoke pencil
New systems don't "push more air", the supply duct guidelines haven't changed, but in the past - and even today, most hvac contractors don't want to do the math to size and route ductwork in the most efficient manner. Your builder may have had an engineer design correct ductwork, but there's a 97% chance it wasn't installed properly even if the design was correct.
Return air is the biggest problem I've encountered - I haven't owned a house yet that had enough. If you aren't pulling an equal amount of air out to the amount you're supplying through the supply ducts, you're pressurizing the room & sending conditioned air outside through outlet holes, baseboards & windows.
The spec for insulated flex ducts has changed over the years, but not enough to cause sweating.
The biggest install problem with flex ducts is calculating the loss in airflow caused by bending them. Air loses a lot of speed in flex duct, and just a couple tight bends (or leaving the ductwork loose & saggy) can turn a textbook install into one that does not deliver the rated airflow by a mile.
I'm being told by an installer that gave me a quote that I need new ductwork. He didn't explicitly say the ductwork is bad or in a state of disrepair. It seemed to have more to do with the type of system he'd be installing needs different ductwork (larger or smaller size? I don't know?). He kind of looked at me funny when I said "How about we get a system that works with what I got?"
I guess this is where I'm confused. Is it that new HVAC systems (he'd be replacing a unit from the 90s) simply can't use "old ductwork" for whatever reason? He did point out that the way things are right now, the volume of air being moved into one room (a bathroom) is equal to the volume of air being pushed into the smallest bedroom.
So sure, there's likely some inefficiencies with old ductwork, but to replace what is currently there that seems to do the job for about $5000 seems unnecessary.
But maybe I'm missing something here. What are valid reasons that I'd need to replace my ductwork? If it matters, we are talking about a split system (condenser outside, air handler in the attic, ducts in attic).
And some installers price their jobs with the duct work comprising very little part of the total bill, so it becomes a "might as well" inclusion on part of the consumer.
My full install was $3500 for a 2 ton XR14, air handler, and duct work in NC. (House is only 1,053 square feet)
Only thing I didn't like was when I asked for a price quote w/o ducts being replaced, installer stated the existing was rated R4 and the new was R8. When I saw the old duct removed, it was plastic-wrapped stating R6.5. I verified the new was R8, but he didn't have to lie and give me inaccurate numbers for me to make a decision.
For an otherwise hard worker and great performing new system, it's a little dark spot in my experience that concerned me.
We had a new heat pump put in yesterday. We chose the company to install it because they did the j-calculations and shared them. They asked a lot more questions about what temp we like in the day and night, how much we are home, how many people etc. They wanted to know if we had a problem area and we said the kitchen has always been too warm.
They suggested a slightly larger duct and when they started the install, they realized the kitchen duct was off of the end of another line. They decided to run the duct directly to the kitchen. What a difference! I’ve usually had to turn on the ceiling fan whenever I’m in there. The tiles are actually cool in there today.
We’ve seen other floor plans of this house that have sold and our kitchen has been switched with the family room. I’m guessing the ductwork was laid out for the kitchen where our family room is. A room where you are up and moving around, like working in the kitchen and then add stove and oven to that, compared to a room where you are likely to be sitting watching TV makes a big difference in how much air they need.
I love this house and I love the kitchen being off on its on from the open area of the living room, dining room and foyer, but the heat issue has been a disappointment. We replaced builder grade windows with impact resistant hurricane ones last year with and that made a difference in the heat from the sun, but didn’t eliminate the heat issue from not enough air flow within the kitchen.
We are so happy we replaced our old unit. It was still working but almost 20 years old and beginning to have some small problems. Living in FL, no AC is not an option in the summer, so we decided to be proactive. We had no idea replacing the unit would end up with a ductwork change that solved our kitchen problem.
We had a new heat pump put in yesterday. We chose the company to install it because they did the j-calculations and shared them. They asked a lot more questions about what temp we like in the day and night, how much we are home, how many people etc. They wanted to know if we had a problem area and we said the kitchen has always been too warm.
They suggested a slightly larger duct and when they started the install, they realized the kitchen duct was off of the end of another line. They decided to run the duct directly to the kitchen. What a difference! I’ve usually had to turn on the ceiling fan whenever I’m in there. The tiles are actually cool in there today.
We’ve seen other floor plans of this house that have sold and our kitchen has been switched with the family room. I’m guessing the ductwork was laid out for the kitchen where our family room is. A room where you are up and moving around, like working in the kitchen and then add stove and oven to that, compared to a room where you are likely to be sitting watching TV makes a big difference in how much air they need.
I love this house and I love the kitchen being off on its on from the open area of the living room, dining room and foyer, but the heat issue has been a disappointment. We replaced builder grade windows with impact resistant hurricane ones last year with and that made a difference in the heat from the sun, but didn’t eliminate the heat issue from not enough air flow within the kitchen.
We are so happy we replaced our old unit. It was still working but 20 old and beginning to have some small problems. Living in FL, no AC is not an option in the summer, so we decided to be proactive. We had no idea replacing the unit would end up with a ductwork change that solved our kitchen problem.
The flexible duct tubing is prone to damage and I have seen quite a few examples of where it has sagged/crimped up where it was supported by a cable tie or strap. So yes, it should be fully inspected to see if there are any flow restrictions or tears that need to be fixed.
How about showing us some pictures of what you have now.
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