central air conditioning installation, high velocity edition
May 28, 2020 8:34 AM Subscribe
We are in the process of getting quotes for installing central air. Yay!!!
Our house does not currently have ductwork. Our options are:
a) Conventional air conditioning with standard rectangular ducts installed
b) High velocity air conditioning (Unico) with mini ducts.
Our house's living space is only one floor, so the a/c handler and ducts would be in the attic, with all supply and return vents in the ceilings of our living space.
We wildly vacillate between conventional and high velocity. Our HVAC guy gave us quotes for 5 systems - 4 conventional and one high velocity. He said, " The Unico system is the most expensive and least efficient of all the systems. We would be fine installing a conventional system in your home as we have plenty of attic space. We typically use Unico systems in tight inaccessible places where conventional duct will not fit."
I don't want the ductwork to take up an inordinate amount of space in the attic, which I talked to him about when he was here assessing our space for the quote.
We were primarily considering the Unico because it would take up less space in the attic, which we use for storage.
I read in many places that high-velocity AC is more efficient than conventional AC, because it reduces humidity much more quickly and efficiently.
I've read that bad installations of high-velocity can be loud.
Does anyone have experience installing or living with high-velocity AC?
(Note: we are not open to mini-splits. Please don't suggest them.)
Our house's living space is only one floor, so the a/c handler and ducts would be in the attic, with all supply and return vents in the ceilings of our living space.
We wildly vacillate between conventional and high velocity. Our HVAC guy gave us quotes for 5 systems - 4 conventional and one high velocity. He said, " The Unico system is the most expensive and least efficient of all the systems. We would be fine installing a conventional system in your home as we have plenty of attic space. We typically use Unico systems in tight inaccessible places where conventional duct will not fit."
I don't want the ductwork to take up an inordinate amount of space in the attic, which I talked to him about when he was here assessing our space for the quote.
We were primarily considering the Unico because it would take up less space in the attic, which we use for storage.
I read in many places that high-velocity AC is more efficient than conventional AC, because it reduces humidity much more quickly and efficiently.
I've read that bad installations of high-velocity can be loud.
Does anyone have experience installing or living with high-velocity AC?
(Note: we are not open to mini-splits. Please don't suggest them.)
How sensitive are you to noise? We have traditional ducting, but for efficiency reasons it is now powered by a much higher velocity fan than the original system. The old systems like they had in the 80s were very quiet because they moved very cold air very slowly. Of course, it's more efficient from a conduction standpoint to create warmer air in the first place, and more efficient to transport it through ducts because the loss is proportional to difference in temperature. So when they installed our new system (this is California, your state may have different rules) they had to bring in an outside inspector to make sure they were pushing the air fast enough. Long story short, our new system, though of overall higher quality, is louder than the old one.
My uninformed guess is that the high-velocity is for people who have no other choice. Plenty of people have small to no crawlspace/attic in which to place ducting, and the question becomes, "Do I want a noisy but efficient whole-house system, or do I want to keep air-conditioning individual rooms?"
posted by wnissen at 9:47 AM on May 28, 2020 [1 favorite]
My uninformed guess is that the high-velocity is for people who have no other choice. Plenty of people have small to no crawlspace/attic in which to place ducting, and the question becomes, "Do I want a noisy but efficient whole-house system, or do I want to keep air-conditioning individual rooms?"
posted by wnissen at 9:47 AM on May 28, 2020 [1 favorite]
I would be surprised if there's a dramatic difference in the amount of usable space one type of ducting takes up over the other, and speaking as a light sleeper I would gladly sacrifice storage space for quiet while I'm trying to sleep.
posted by mhoye at 9:48 AM on May 28, 2020 [1 favorite]
posted by mhoye at 9:48 AM on May 28, 2020 [1 favorite]
I don't know about the specific high velocity unit you're looking at or the specific conventional units you're looking at. However, you'll likely see SEER ratings around 11 for high velocity and 13-14 for conventional units. The "dirty secret" of high velocity units is that their AC compressor efficiency is reasonable - but they need a massive, somewhat inefficient, and generally loud blower fan to move air. You can look at a energy savings calculator to see if this makes enough of a monetary savings for you to care.
Your installer will tell you the high velocity unit can be made as quiet as a conventional unit. They're generally correct if you just measure by decibels (loudness). However, high velocity units tend to sound like there's wind going around your house as opposed to the more "background" white noise that you get from a conventional unit. So, it might be equally as loud (best case), but people tend to notice the high velocity noise more.
Even if the high velocity unit isn't too loud for you, it's also... high velocity. You'll be noticeably uncomfortable being around the outlets due to the air velocity. There are also generally more outlets than you expect, since installers want to use 6-7 of them per ton of cooling.
High velocity units are not "bad" - they're an adequate solution to houses that have minimal space for ducts and air handlers. Essentially their only advantage is their size. That shouldn't be discounted if you have limited storage area in your house. However, in every other way, high velocity units are inferior to conventional.
(or mini-splits, can be ducted just like conventional units!)
posted by saeculorum at 10:16 AM on May 28, 2020
Your installer will tell you the high velocity unit can be made as quiet as a conventional unit. They're generally correct if you just measure by decibels (loudness). However, high velocity units tend to sound like there's wind going around your house as opposed to the more "background" white noise that you get from a conventional unit. So, it might be equally as loud (best case), but people tend to notice the high velocity noise more.
Even if the high velocity unit isn't too loud for you, it's also... high velocity. You'll be noticeably uncomfortable being around the outlets due to the air velocity. There are also generally more outlets than you expect, since installers want to use 6-7 of them per ton of cooling.
High velocity units are not "bad" - they're an adequate solution to houses that have minimal space for ducts and air handlers. Essentially their only advantage is their size. That shouldn't be discounted if you have limited storage area in your house. However, in every other way, high velocity units are inferior to conventional.
(or mini-splits, can be ducted just like conventional units!)
posted by saeculorum at 10:16 AM on May 28, 2020
I would be surprised if there's a dramatic difference in the amount of usable space one type of ducting takes up over the other, and speaking as a light sleeper I would gladly sacrifice storage space for quiet while I'm trying to sleep.
It really depends on the installers - our house is old so it's installed like octopus arms running everywhere and the warm air return pipe is 24" diameter - it's pretty big. The AC ducting makes many parts of the attic inaccessible unless you are a gymnast.
posted by The_Vegetables at 1:13 PM on May 28, 2020
It really depends on the installers - our house is old so it's installed like octopus arms running everywhere and the warm air return pipe is 24" diameter - it's pretty big. The AC ducting makes many parts of the attic inaccessible unless you are a gymnast.
posted by The_Vegetables at 1:13 PM on May 28, 2020
When researching houses to purchase, one of our requirements was traditional ductwork. Many high velocity houses do so because there is no other choice, and it is often cheaper. There are many reports of them not being able to "keep up" with the cooling demands of the house (because of the retrofit-nature, installers often did a poor job, it was underbuilt, etc). Also, they have a specific look to them that we don't prefer.
As for your attic space, even if the ducting took a lot of space, you could install shelves or other storage solutions for a fraction of your AC budget. I wouldn't personally even consider that as a limiting factor.
posted by bbqturtle at 1:18 PM on May 28, 2020
As for your attic space, even if the ducting took a lot of space, you could install shelves or other storage solutions for a fraction of your AC budget. I wouldn't personally even consider that as a limiting factor.
posted by bbqturtle at 1:18 PM on May 28, 2020
I barely notice the sound of the HV system installed in my sister's house. Not sure when it was installed, and given the massive soffits it runs through it likely replaced a standard ducted system.
The ducted system in my house is at least 20 years old and is loud as heck. I think our registers are original 1940s ones, so that might be part of it.
So there's a data point.
posted by MonsieurBon at 1:19 PM on May 28, 2020 [1 favorite]
The ducted system in my house is at least 20 years old and is loud as heck. I think our registers are original 1940s ones, so that might be part of it.
So there's a data point.
posted by MonsieurBon at 1:19 PM on May 28, 2020 [1 favorite]
We have a Unico system throughout our three story, 1912 home that has had its attic converted into living space.
Architecturally, it's a work of art. The designers were able to preserve the classic interior design of the home, as well as opening up the attic into living quarters, while making the entire space air conditioned without any visible ductwork. All of the ducting is hidden in closets, in the tight space between floors, and in a few areas, a very small (6" or so) channel that's been architecturally integrated with the home. Other than the presence of the little Unico portholes in each room, you'd never guess the house was outfitted for air conditioning. You wouldn't even think there were ducts.
The Unico is not nearly as quiet as a modern ducted system (which can be virtually silent), but it is not nearly as loud as older ducted systems, like the one in my parents' house. You'll certainly hear the system turn on and off, and there's a low-level whoosh while the system is in operation, but it's not particularly loud - it's the sound of air pushed through a smaller channel. You wouldn't struggle to hear, say, music or a TV over it.
Our system is effective at holding temperature, but it struggles if you ask it to substantially lower temperature. It's the kind of system that you set to a temperature at the beginning of the season, leave it there, and the system will indeed hold things to that temperature. However, if you turn it off and the house gets up to the high 80s, it's going to be hours and hours before it's back down in the low 70s. It honestly doesn't work well with a smart thermostat for this reason.
Costs of operating the system on a square foot basis seems similar to other systems I've used. I've done a lot of reading on the system, and in the end, I just don't know who to believe in terms of the efficiency question versus ducted systems.
While the Unico system excels at integrating with living spaces and multi-story houses, and is really the only way our house could have AC without ruining it, if I were in a more conventional home with a conventional attic, and a ducted system were substantially cheaper, I might indeed go with that and "work around" the ducts in the attic - or purchase external storage with the savings. In the end, I think the decision has much to do with the higher cost of the Unico versus the convenience of the amount of extra space it will provide in your home, and whether that cost is worth it to you for the specific amount of extra space it makes possible.
posted by eschatfische at 2:51 PM on May 28, 2020 [2 favorites]
Architecturally, it's a work of art. The designers were able to preserve the classic interior design of the home, as well as opening up the attic into living quarters, while making the entire space air conditioned without any visible ductwork. All of the ducting is hidden in closets, in the tight space between floors, and in a few areas, a very small (6" or so) channel that's been architecturally integrated with the home. Other than the presence of the little Unico portholes in each room, you'd never guess the house was outfitted for air conditioning. You wouldn't even think there were ducts.
The Unico is not nearly as quiet as a modern ducted system (which can be virtually silent), but it is not nearly as loud as older ducted systems, like the one in my parents' house. You'll certainly hear the system turn on and off, and there's a low-level whoosh while the system is in operation, but it's not particularly loud - it's the sound of air pushed through a smaller channel. You wouldn't struggle to hear, say, music or a TV over it.
Our system is effective at holding temperature, but it struggles if you ask it to substantially lower temperature. It's the kind of system that you set to a temperature at the beginning of the season, leave it there, and the system will indeed hold things to that temperature. However, if you turn it off and the house gets up to the high 80s, it's going to be hours and hours before it's back down in the low 70s. It honestly doesn't work well with a smart thermostat for this reason.
Costs of operating the system on a square foot basis seems similar to other systems I've used. I've done a lot of reading on the system, and in the end, I just don't know who to believe in terms of the efficiency question versus ducted systems.
While the Unico system excels at integrating with living spaces and multi-story houses, and is really the only way our house could have AC without ruining it, if I were in a more conventional home with a conventional attic, and a ducted system were substantially cheaper, I might indeed go with that and "work around" the ducts in the attic - or purchase external storage with the savings. In the end, I think the decision has much to do with the higher cost of the Unico versus the convenience of the amount of extra space it will provide in your home, and whether that cost is worth it to you for the specific amount of extra space it makes possible.
posted by eschatfische at 2:51 PM on May 28, 2020 [2 favorites]
This thread is closed to new comments.
posted by mightshould at 9:44 AM on May 28, 2020 [2 favorites]