More Q&A Spotlight
Member SNMC is thinking about installing a high-velocity HVAC system for his new home in Climate Zone 7A. A high-velocity system uses an air-handler that distributes air at a higher pressure through smaller diameter ducting, increasing the rate of airflow and, theoretically, its efficiency. (For more on velocity and airflow rates, see The Best Velocity for Moving Air Through Ducts.) The smaller ductwork is also supposed to be easier to install in tight spaces. His builder’s HVAC vendor recommended the system; the vendor told SNMC that high-velocity systems have been used in residential builds.
SNMC goes on to say that a heat pump will be the primary HVAC driver. He also plans to install a hydronic system in the finished basement with a TV/rec room and spare bedroom, which he hopes can provide auxiliary heat to the upstairs space. (He admits that hydronic systems are expensive, but thinks the comfort is worth the cost.)
So, is a high-velocity HVAC system a good plan? This is the topic for today’s Spotlight.
Do drawbacks outweigh benefits?
Both Patrick Osullivan and Peter Engle testify to high-velocity systems’ ability to cool things down in the summer, and Engle says they are very good at dehumidification. Osullivan had a Unico high-velocity system in his home and says another benefit is that the smaller ductwork can be placed where larger ducts can’t fit.
Generally, though, the members posting in this thread don’t show a lot of love for high-velocity systems.
On the subject of size, members DCcontrarian and Akos add some insight. DCcontrarian writes that “high-velocity systems are rare in new construction, and … they’re usually used in retrofits, where they can be used in places where there’s no room for ductwork.” Akos points out that while the systems’ branch lines…
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9 Comments
When I attended the Better Building Better Business conference in Green Bay, WI in 2004 I believe, high velocity HVAC was featured in at least one home we toured. Never heard much about it after
that. I like the idea of smaller ductwork but with a typical velocity and very energy efficient building.
Doug
This is exactly the conundrum I am experiencing now. These excellent systems are excellent in new homes. I have a beautiful 110 year old Craftsman home I am starting a major remodel on to increase its energy efficiency. If I chop large portions of the rooms and ceiling height I can install all these wonderful large ducts or mini-splits. Also my floor joists are limited to the 2x10's that it was built with. I would like to continue to heat with the cast iron radiators with a new heat-pump "boiler". But trying to get AC and fresh air is a hair pulling effort. I would certainly not put a SDHV system into new construction but it does have its place. Too bad it is 2.5 times $ a regular system. It may be a bit noisier but have you tried to watch TV next to a portable AC unit? Energy Vanguard does not have answers for old homes it seems. Would the energy saving/fresh air group of us want us to tear down these old homes instead to build new? That doesn't seem very carbon neutral.
estebang,
"Energy Vanguard does not have answers for old homes it seems. Would the energy saving/fresh air group of us want us to tear down these old homes instead to build new? That doesn't seem very carbon neutral."
Where in the article did you get anything that drew you to those conclusions? Allison doesn't generally recommend high velocity systems. That doesn't mean he is telling you to burn down your house, or has no ideas about how to incorporate HVAC into older structures.
You are correct. It is a bit of a rant of my frustration. I apologize for bringing Allison in to it. I did reach out to make contact but thru whatever means it did not work out. I understand he is not in control of what equipment is out there. Although there is a definite lack of interest in attacking old homes from the general movement. I have reached out to many consultants and designers with many a lack of reply. Either so busy they cannot, or hear what the job is, and wither on the vine. Ranting off and I will better construct questions / replys from here on.
When renovating old homes, your options are limited if you want to preserve the original look. That's your choice, not the fault of the consultant. Wall-mounted mini-splits solve a lot of problems but some people find them unattractive. They are not bad looking if you prioritize comfort and efficiency.
Air-to-water systems are promising but the water temperature they put out doesn't work with legacy systems unless they were grossly oversized.
If you can get your building envelope efficient enough, you might consider one of these combination units:
https://www.minotair.com/home_us/?doing_wp_cron=1708616563.7287321090698242187500
https://buildequinox.com/?gclid=CjwKCAiA_tuuBhAUEiwAvxkgTslwZk3Se8T5TnRwxZB1V68PSFgph_R_1IVZhQCnRDjFqoddySWV_BoC1JYQAvD_BwE
I was thinking those units were interesting on the get go, but when you really pencil out the system efficiency, it's quite low in comparison to a basic ERV combined with a basic heat pump. If it's a new build, a bottom shelf panasonic ERV fed into the return duct of any basic ducted minisplit will net a better system efficiency and cost less. The problem is, you completely lose the "free" heat exchange properties of a traditional ERV by doing all the heat exchanging mechanically through the heat pump, and even though it extracts more heat out of the outgoing air, it does so at the cost of running the pump. And in the end, it only can extract so much heat before that outgoing air is below the temp of the incoming air.
" Wall-mounted mini-splits solve a lot of problems but some people find them unattractive. They are not bad looking if you prioritize comfort and efficiency."
Sadly, with Instagram and design shows, looks often take a oversize role in choices. I asked a Designer about all the Aria vents she was spec'ing for house and how they would compromise airflow. She said, form over function. I thought, I could never work with you. Function first, then make it look nice. Her clients were all in as were others from another house I spoke with. They said they would follow their Designer 100% since they wanted it to look nice. She told them to put a huge Town and Country gas fireplace in a office that was about 12x12. They are going to need a fire suit when the turn on a 50,000 BTU fireplace in such a small room. But it will look nice when it's not on.
It's something I deal with daily, as I'm not able to talk many of my clients into mini-split systems so they end up spending far more on other systems that don't work quite as well.
I like the efficiency of minisplits but honestly I don't like the idea of servicing and cleaning several minisplits throughough the house; from that point of view a centralized HVAC sounds easier to manage in the long run. Then there is the filtration issue and the house layout basically has to be open. So estetics is not the only limit with miniplits.
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