This is a question/situation that we deal with on a daily basis, especially this time of year. Customers have a room/rooms or an entire floor of the home that is uncomfortable and they do what they are able to attempt improving the comfort in their home. Besides adjusting the thermostat up or down, the only other readily accessible "control" they have over their heating and cooling is the supply registers in their living space. Some fine tuning of the supply registers to balance the system and direct airflow is reasonable and acceptable; however, more often than not we find folks have completely closed off entire rooms or even floors in attempt to direct their heating or cooling airflow to uncomfortable areas of their home or perhaps in a misguided attempt at saving money on heating and cooling costs. Let's look at those reasons in more detail and talk about why it really isn't a good idea in almost every case.
First, let's talk about energy savings because that one is pretty clear-cut. Closing vents to save money in heating and cooling costs will generally not work and could even cost you more. That might sound counter-intuitive - if I'm heating/cooling less of my home, how can that cost more? There was actually a study performed by Lawrence Berkeley National Laboratory back in 2003 that showed just that. Now, that test simulated a home in California with a single, large central return and ductwork in unconditioned space. Here in Northwest Indiana and South Chicagoland we typically have ductwork in conditioned basements with return registers in most rooms rather than a central return. So, I believe the conclusion is the same but for a couple of different reasons.
When you close off the supply registers to a room you do a couple of things. We'll assume it's heating season and you're trying to save some money by not heating a room you don't use often, so you close the register(s) in that room and close the door. What you can't keep from happening by doing that is the cold coming through the walls, ceilings, floors, and windows. It will cool off that room just the same as it did before. In fact, if it gets cold enough, you may find yourself fighting condensation problems on the walls and ceilings of that room which can damage materials and even lead to mold growth.
Two things then occur -- since very few people have insulation inside interior walls and doors, that cold will come into the house just like it always has. Also, the return duct inside that room is going to draw in the now colder air from within the room, and since we've shut off the supply vent it will create a negative pressure inside the room that will increase the infiltration of cold air through any cracks or crevices.
You also increase what is known as the static pressure inside the ductwork of your home. Higher static pressure is going to affect the airflow through your furn and to your entire home. If you have a standard blower motor on your furnace, higher static pressure is actually going to slow down the fan and decrease airflow to the entire home. It can actually get low enough that the heat being created inside the furnace is unable to get out quickly enough and the furnace can overheat and hit the high limit, causing it to shutdown. Repeatedly running on high limit is terrible for the furnace and will significantly shorten the life of the components, especially the heat exchanger. The problem is similar in the summer - low airflow can lead to a frozen coil which could lead to liquid refrigerant making its way to the compressor which can kill that vital component in short order. In other words, you can literally destroy your important and expensive heating and cooling equipment with something as seemingly harmless as closing a few vents.
So what should we do when we want to save money on Heating and Cooling? Installing more efficient equipment is a surefire way to reduce your energy cost/consumption. What else? Reducing your load by better sealing, windows, and insulation is another option. By simply reducing the amount of heat that is being gained/lost through the walls, ceilings, and floors we make less work for the HVAC equipment. Finally, turning the temperature in your home down in the winter and up in the summer can make a big difference. Either all the time (wear sweaters in the winter) or through the use of a properly programmed thermostat can make a large dent in one of your largest costs. Finally, getting your equipment professionally tuned-up every year can make a huge difference in efficient and safe operation.
If you have a variable speed blower in your furnace you are benefiting from the more energy efficient design of the motor at regular speeds. However, when faced with increased static pressure from closed vents, a variable speed blower will do what it can to still match the requested airflow which means spinning faster and working harder, sometimes to an extreme. At that point you are using much more energy to run the system, it will be much noisier and you certainly won't be saving any money.
The event that inspired this article was a customer with a 3 year old furnace that needed to have the heat exchanger replaced last year once again had over 50% of their registers closed in the home. That customer must have comfort issues they are trying to solve by closing registers, so let's talk about that.
If you have a single room that is getting too much heat in winter (or cooling in the summer) I think it is alright to close the register into that room. Assuming you have at least 10 registers in your home, you're reducing available airflow by less than 10%, something most systems can handle. What isn't OK is when people have a single room that isn't getting ENOUGH heat so they try to close all the OTHER registers to "force" the air where they want it. As we discussed before, closing registers will actually decreases all the airflow in the house to the point that it may be causing damage to your heating and cooling equipment. Also, decreased airflow throughout the home is likely to cause new comfort problems in other rooms where there were none before.
So, what's a person to do when they have comfort problems in their home? Here at Illiana, we face a lot of these comfort concerns every day and we thankfully have a number of solutions to offer.
Multi-stage and variable capacity equipment can go a long ways to improving home comfort and often improve efficiency at the same time. Being able to more closely match the output of the heating and cooling equipment to what your home actually needs at the time allows for longer run-times which allows airflow to circulate through all the rooms of the house at a slower rate, rather than experiencing the "blast furnace" effect with equipment that is larger than it needs to be in the winter or the "meat locker" in the summer.
That 2-stage or variable speed equipment also comes with a critical component - a variable speed blower motor. A key feature is the ability to run the blower all the time - even when not heating or cooling - at a low speed that is quiet and energy efficient but allows air to circulate throughout the home to keep temperatures much more even between rooms and even between floors. If you're not due for or can't afford new equipment, there's good news - we can retrofit a version of the variable-speed motor into most furnaces to get the same energy savings and comfort benefits.
What about homes with multiple floors that just aren't comfortable? That's a great application for zoning. Properly designed and installed zoning systems allow different temperature zones within a home with existing equipment to provide comfort and savings unavailable any other way. In my own home, a zoning system was the only way to have both floors be comfortable at the same time. Before I installed the zoning system it was either way too cold or way too hot upstairs depending on the season and I simply could not get it right up there for any length of time. Zoning solved the problem for me and it could for you too.
Finally, the addition of another source of heating or cooling may be the solution. We've helped a number of folks that have beautiful 4-season rooms and bonus rooms that were never comfortable until we added a ductless Heating and cooling system for them. Sometimes areas have insufficient ductwork or have a temperature and climate so different from the rest of the home they simply need their own heating or cooling. We've even done bedrooms in homes where someone needed different temperatures than the rest of the house and a ductless system solved that problem. By simply adding an independent source of heating/cooling to the problem area you are then free to let the main system take care of the rest of the home as intended. While a higher cost option, sometimes it is the only thing that can truly make things comfortable and efficient.
So, to recap, here are the downsides to closing registers:
- Lower airflow with standard furnace blowers
- Higher energy usage and noise with a variable speed blower
- Increased room infiltration possible from localized negative pressure
- Possible condensation in closed off rooms, potential mold growth
- Comfort problems from reduced airflow throughout the home
- Frozen evaporator coils that cause cooling problems
- Dead compressor from frozen coil
- Cracked heat exchanger from low airflow through furnace which leads to potential Carbon Monoxide poisoning
So, if you find yourself with comfort problems or you're looking to reduce your heating and cooling bill, don't close registers. Instead, give us a call and see if we can't help give you a real solution to your comfort needs. After all, we're Your Christian Owned and Operated Neighborhood Comfort Specialists Since 1987!