Can You Save Money by Closing HVAC Vents in Unused Rooms?
Energy Vanguard Blog
Your air conditioner, heat pump, or furnace probably uses a lot of energy. Heating and cooling makes up about half of the total energy use in a typical house. For air conditioners and heat pumps using electricity generated in fossil-fuel fired power plants, the . A question I get asked frequently is whether or not it's OK to close vents in unused rooms to save money. The answer may surprise you.
The photo above shows a typical vent for an ducted HVAC system (air conditioner, heat pump, or furnace). On the return side, you'll typically see plain grilles, but on the supply side, where the conditioned air gets blown back into the house, most HVAC contractors install registers like the one above. It has a lever of some sort that allows you to adjust the louvers behind the grille.
You'd think that since it's adjustable, it must be OK to open or close it to suit your needs, right?
The blower and the blown
The blower in your HVAC system is the heart of the air distribution. It pulls air from the house through the return ducts and then pushes it back into the house through the supply ducts. In high-efficiency systems, the blower is powered by an electronically commutated motor (ECM), which can adjust its speed to varying conditions. The majority of blowers, however, are of the permanent split capacitor (PSC) type, which is not a variable speed motor.
In either case, the system is designed for the blower to push against some maximum pressure difference. That number is typically 0.5 inches of water column (iwc). If the filter gets too dirty or the supply ducts are too restrictive, the blower pushes against a higher pressure.
In the case of the ECM, a high pressure will cause the motor will ramp up in an attempt to maintain proper air flow. An ECM is much more efficient than a PSC motor under ideal conditions, but as it ramps up to work against higher pressure, you lose that efficiency. You still get the air flow (maybe), but it costs you more.
The PSC motor, on the other hand, will keep spinning but at lower speeds as the pressure goes up. Thus, higher pressure means less air flow, and, as we’ll see below, low air flow can cause some serious problems.
The important thing to remember here is that no matter which type of blower motor your HVAC system has, it's not a good thing when it has to push against a higher pressure.
Closed vents increase pressure
In a well-designed system, the blower moves the air against a pressure that's no greater than the maximum specified by the manufacturer (typically 0.5 iwc). The ideal system also has low duct leakage.
The typical system, however, is far from ideal. Although most systems are rated for 0.5 iwc, the National Comfort Institute, which has measured static pressure and air flow in a lot of systems, finds the typical system to be pushing against a static pressure of about 0.8 iwc. Now we're ready to address the question of closing vents.
When you start closing vents in unused rooms, you make the duct system more restrictive. The pressure increases, and that means an ECM blower will ramp up to keep air flow up whereas a PSC blower will move less air. Most homes don't have sealed ducts either, so the higher pressure in the duct system will mean more duct leakage, as shown below.
The more vents you close, the higher the pressure in the duct system goes. The ECM blower will use more and more energy as you do so. The PSC blower will work less but not move as much conditioned air. In both cases, the duct leakage will increase further.
What about heat?
In addition to moving air, your air conditioner, heat pump, or furnace is also cooling or heating that air that flows through the system. The air passes over a coil or heat exchanger and either gives up heat or picks up heat.
In a fixed-capacity system—and most are—the amount of heat the coil or heat exchanger is capable of absorbing or giving up is fixed. When the air flow goes down, less heat exchange happens with the air. As a result, the temperature of the coil or heat exchanger changes.
If air flow is low, it'll dump less heat into the coil in summer, and the coil will get colder. If there's water vapor in the air, the condensation on the coil may start freezing. You might even end up with a block of ice, as shown in the photo below. And ice on the coil is really bad for air flow.
It's also bad for the compressor as not all of the refrigerant evaporates and liquid refrigerant makes its way back to the compressor. If you want to have to buy a new compressor, this is a good way to do it.
Same thing if you have low air flow over a heat pump coil in winter. You could get a really hot coil, high refrigerant pressure, and a blown compressor or refrigerant leaks.
Similarly, low air flow in a furnace can get the heat exchanger hot enough to cause cracks. Those cracks, then, allow exhaust gases to mix with your conditioned air. When that happens, your duct system can become a poison distribution system as it could be sending carbon monoxide into your home.
9 unintended consequences of closing vents
Let me now summarize the problems I've described above that can result from closing vents in your home. The first thing that happens is the air pressure in the duct system increases, which may give rise to these negative consequences:
Increased duct leakage
Lower air flow with PSC blowers
Increased energy use with ECM blowers
Comfort problems because of low air flow
Frozen air conditioner coil
Dead compressor
Cracked heat exchanger, with the potential for getting carbon monoxide in your home
, as I described last week
Condensation and mold growth in winter due to lower surface temperatures in rooms with closed vents
You're not guaranteed to get all the problems that apply to your system, but why take the chance.
A Kickstarter project to avoid
I recently wrote about all the IT folks who are trying to follow in Nest's footsteps and profit from the home energy efficiency movement. I used the
as the example of companies that think you can solve problems just by creating a product with a smartphone app.
Well, meet a more malignant idea: the E-vent. (You can find it easily enough by searching on the term "Kickstarter E-Vent.") It's just a Kickstarter project right now, and maybe it won't get funded. If it does get funded, however, it will be subject to all the problems I described above. It doesn't matter whether you close the vents by getting up on a ladder in your home or from the beach in Cozumel. It's still a bad idea.
The E-Vent page on Kickstarter says they monitor the air temperature and open vents if the temperature gets too cold while air conditioning or too hot while heating. Of course, that’s not going to work unless they monitor the temperature right at the coil or heat exchanger. And that still probably wouldn’t work because there’s a wide range of acceptable temperatures for different systems.
This is an HVAC product developed by people who don't know some very important principles of heating and air conditioning. Let's hope they don't kill anyone.
The only way closing vents could work
The fundamental problem here is that closing supply vents in your HVAC system changes what comes out in particular locations. It doesn't change what the blower is trying to do. Nor does it change the amount of heat the air conditioner, heat pump, or furnace is trying to move or produce.
It's possible you may be fine closing a vent or two in your home, but it will depend on how restrictive and leaky your duct system is. If it’s a typical duct system with 60% higher static pressure than the maximum specified, closing even one vent could send it over the edge. If it’s a well designed system with low static pressure and sealed ducts, you shouldn’t have a problem as long as you don’t try to close too many.
The only way something like this could work is if closing a vent signaled the blower to move less air and the air conditioner, heat pump, or furnace to move or produce less heat.&(Properly designed zoned duct systems do this by using variable speed ECM blowers with multi-stage systems.) Otherwise you're subject to those 7 unintended consequences, one of them potentially deadly.
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Thanks to Curt Kinder, David Butler, John Semmelhack, Eric Sandeen, and Dale Sherman for suggestions in the comments below that made this article better and more complete.
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make the door open和mmake the door opened那一个对?为什么?
make the door open和mmake the door opened那一个对?为什么?
make加双宾语结构,其中用形容词做宾语补足语.所以应该用open就可以了
open 就好了，是形容词。不需要用 opened。如果有动词的固定搭配,比如make sb do sth 这里的这个do用不用考虑时态问题,比如说he made me to open（opened） the door yesterday那个对?_百度作业帮
如果有动词的固定搭配,比如make sb do sth 这里的这个do用不用考虑时态问题,比如说he made me to open（opened） the door yesterday那个对?
如果有动词的固定搭配,比如make sb do sth 这里的这个do用不用考虑时态问题,比如说he made me to open（opened） the door yesterday那个对?
这个显然是前面的对,不需要考虑时态问题,因为make 是一个典型的使役动词,后面接动词原形,属于固定搭配 下面是详解役动词 使役动词 1.使役动词是表示使、令、让、帮、叫等意义的不完全及物动词,主要有leave.get.keep.make(使,令),let(让),help(帮助),have(有；让；从事；允许；拿)等.2.使役动词后接受词,再接原形不定词作受词补语.接宾语时,人称代词用宾格.He made me(宾格) laugh.他使我发笑.I let him go.我让他走开.I helped him repair the car.我帮他修理汽车.Please have him come here.请叫他到这里来.3.使役动词还可以接过去分词作受词补语.I have my hair cut every month.我每个月理发.4.使役动词的被动语态的受词补语用不定词,不用原形不定词.(主)He made me laugh.他使我笑了.(被)I was made to laugh by him.我被他逗笑了.使役动词有以下用法：a.have somebody do sth让某人去做某事 I had him arrange for a car.b.have somebody doing sth.让某人持续做某事.He had us laughing all through lunch.注意：用于否定名时,表示“允许” i won't have you running around in the house.我不允许你在家里到处乱跑.使役性动词（Causative Verb） 1.make /have/ let +sb +do sth.2.get/set/leave + sb to do/doing sth.
无需考虑时态问题，时态只体现在make这一动词上
不用考虑He made me open the door yesterday 才对made已经是过去时态了 希望能够帮到楼主
不需要。这里的do的意思就是动词原形的意思。
应该是原型open，介词to后面加动词原形。您的浏览器版本过旧
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