Just about all the HVAC-related sites indicate that shutting off vents (“registers” in the industry parlance) can potentially damage your unit because it adds stress to you unit and duct work since it increases pressure.
All sounds plausible, but the FQ: Are there any actual studies to show how much sooner it can damage your unit and venting than if you left them all open?
JFTR: I don’t do this, and have never heard of anyone doing this until I saw this discussion on ‘another forum’ elsewhere.
The damage won’t be to the ductwork or the fan, they can easily handle the slightly higher static pressure with no problems. The real problem is from the overall lower airflow - the refrigerant coil is designed to have a certain amount of airflow through the coil, around 400 cubic feet per minute (CFM) per ton of cooling capacity. Maybe a bit more or less, but around 400 CFM per ton. If there is not enough air through the coil, the coil may ice up. At any rate, low airflow can change the suction and discharge pressures across the compressor, which might cause problems.
Note that the fan and ductwork have to deal with air pressure, and the compressor has to deal with refrigerant pressure. The compressor is the expensive bit of the system.
Why then do they make the registers with closeable vents? Seems counter-intuitive.
The closeable part of register is called a damper, and they are needed to balance the airflow in a duct system. It’s a bit of an effort to design a duct system that is close to being naturally balanced, and even if you did design it, the installer will have other ideas that necessitates the use of dampers. Even so, you shouldn’t have a damper 100% closed, but people are people, what are you going to do?
In that case, you shouldn’t have a damper that can be 100% closed. And yet, we do.
I may be wrong, but I thought the dampers were inside the ductwork and controlled by the thermostat? I’m speaking of the the louvered, covered openings in the ceiling that have a slide to open and close.
Yes, it was explained to us that everything needs to be a constant except for the computer controlled temperature settings in order for HVAC to stay healthy and work accurately. No vents are to be closed, no classroom/office windows opened, etc.
Residential grills, diffusers, registers, whatever you want to call them, are the cheapest available in most cases. People want high dollar kitchens, flooring, etc. but won’t spend more than three bucks on the entire duct system. Commercial and industrial systems can be much better because buyers of those systems have specific requirements and can spend the money needed to meet them. Very rare for a homebuyer to do so.
The more vents that are closed, the more resistance the blower motor will feel when trying to push air into the house. It’s going to be more of an issue the more vents are closed. Closing one vent is no big deal. Closing half the vents may cause problems.
Also, a lot of people mistakenly think that closing a vent will mean that vent’s air will be directed to another vent. That is, they think the airflow is still 100% of what it was even with the vent closed. But the overall airflow in the house is actually reduced for each vent closed. This means that your HVAC may have to run longer in order to reach the desired temperature, which means more wear-and-tear on the system. That might be an okay tradeoff if it means a hot part of the house is more comfortable with certain vents closed off.
I’ll clarify that I am assuming that the OP is talking about a run of the mill residential central AC system, which usually do not have dampers controlled by a thermostat. However, on commercial systems and higher end residential systems, yes, such dampers can be in a system.
Does the blower actually experience resistance? It might speed up and maybe cause the blower motor to overheat and wear the bearings faster. You can hear that effect if you block either the inlet or outlet of a vacuum cleaner. When it’s not moving air the motor will speed up, but then could overheat if run too long.
Hmm. I’ve never lived in a house (as and adult) that didn’t have thermostat-controlled dampers. Who knew?
I’ve never lived in a house with AC, so who knew opening and closing dampers was a thing.
I always have, and I can’t say I’ve ever heard of shutting them off completely.
Usually what I’ve run across is when there’s a small room like a home office with a register in the ceiling, and the corresponding ac or heat is too much for that space, so whoever’s in there will adjust the register to keep that room comfortable and similar to the rest of the house rather than like a little walk-in freezer or oven.
Otherwise, they’re almost all left wide open as a matter of course- from what I understand for central ac/heat you want full airflow on both the return and the output ducts, so that the air gets well mixed and the thermostat can run the ac/heat appropriately.
Well this sucks to consider. I have a brand-new heat pump after my ~28 year old Ruud finally died. The problem is I also have a new thermostat and it doesn’t seem to kick on the AC as eagerly as the old one did. The thermostat is on the first floor and it was getting up to 80 on the second floor even with the thermostat set to 74.
My solution was to close some of the first-floor vents so the first floor and the thermostat wouldn’t get cooled as quickly and hopefully more cool air would go upstairs. It’s been working but I don’t want to damage anything. I’ve already been warned by the techs that the new units aren’t built as well as the old ones.
What might work better is to get some register fans to pull more air into the hot areas. They replace the plain vents in those rooms and have fans to pull more air into the room. Some of them have sensors so they only turn on when the HVAC system turns on. They can help pull extra air into those rooms and make them more comfortable. But they might only help with a small temperature difference.
I had a similar situation with a hot upstairs and the register fan wasn’t sufficient. This was a loft apartment with only one vent in the loft. The register fan was too weak to make a difference. It helped a bit, but there was still too much of a temperature difference. What I ended up using was an actual duct fan that could move a significant amount of air. A duct fan is a fan that is meant to be installed in the ducts itself. I removed the register and put the duct fan in the incoming duct and that moved enough air to keep the loft cool.
If you have a duct/register fan that doesn’t have a sensor to know when to turn on, one option is to plug the fan into a Temperature Controlled Outlet. Rather than the fan only coming on when the HVAC is on, the outlet can turn the fan on if the room gets too hot. Even if the HVAC is off, the fan will pull cooler air from other parts of the house into the hot room.
I had never heard of register fans but yeah those seem like a good option especially if the register is close to a power source/plug.
Even at 100% they still leak a bit, so no they are not 100%. However yes most HVAC systems can afford to close 1 of them, some even 2, after that it may cause undesirable things.
But another reason is sometimes you are not running an air conditioner but just the fan which has far less issue with closing down more vents.
Most dampers, if they even have them, are not controllable. They are set with handles.
Very few people have zone control with dampers in their homes.
Closing registers on the first floor shouldn’t be a problem. You may get more cold air upstairs, but the real problem is getting the hot air in the room back to be cooled through the returns. Heat rises and cold air will sink down, so it probably works fine in the winter, but has trouble in the summer. Most returns are not controllable at all, but people cover them with furniture or block them some way.
I most definitely have electronic-controlled dampers, as do everyone in my neighborhood.