Why Closing your Air Vents Will NOT Save you Money???

[Arnie Goetchius]

A local Plumbing contractor says the following:

?In the case of a central heating and air conditioning system, closing off vents has the same effect as a dirty air filter. It simply restricts airflow. Heating systems are designed to heat the whole home and are sized accordingly. Shutting off a section of airflow increases the air pressure in the system, in turn increasing the amount of duct work leakage."

"A more energy efficient way to control individual temperatures in unused rooms is by using a ductless heating and cooling mini split systems that are mounted on the wall and wired using a simple wiring process to an outdoor unit. No ducts are used so installation doesn?t take much time at all. Ductless heating and cooling mini split systems are a flexible solution.?

My question: Is closing the ducts to three unused bedrooms and an unused bathroom a bad idea and it won?t save any money on the gas bill?

[clare]

Correct You make the furnace work harder and less efficiently by closing off the ducts unless your furnace is undersized for the home (which is EXTREMELY rare. Most furnaces are at least 50% oversized

[trader_4]

Wrong. There is no such thing as "working harder". If you have a couple rooms that are unoccupied and you close them off and close off the heating vents, you will burn less fuel, because you're heating less space. And if you have leaky ducts, they need to be fixed. In extreme cases, if you closed off a lot of vents then you could have problems, more likely with ] AC than with heating. I have two rooms cut off that way, heating system works fine.

[Unquestionably Confused]

While I agree that closing off ductwork will increase the back pressure and cause "leakage" (unless the installer was absolutely anal about sealing all seams and joints with metal tape, etc) the only downside that I visualize is that the blower motor will have to work harder.

Let's look at an average home of ~1500 sq feet with 3 bedrooms and the thermostat for the FANG system centrally located in, say, the living room or central hallway.

We close off all three BR vents directing the total output of the furnace to the Kitchen, LR, Dining Room, Hall and Baths. Seems to me that its going to more quickly bring the area where the thermostat is located up to temperature and then shut down. This, I think, would be especially true if the BR doors were also closed during this period.

Giant savings? Likely not, but if you're not heating a third (?) or half (?) the house, how can there not be some savings realized?

It's not that unusual to adjust temps differently in different areas. In our case, we have a combo of electric baseboard heat and ducted central air. We built in 1974 and, believe it or not, the next time the heat is turned on our bedroom will be the first time (other than an initial test to ensure it was properly wired and working). We like it cold for sleeping. Winter time it's rarely above 55 degrees in there provided we don't close the bedroom door.

[TimR]

On Wednesday, January 27, 2016 at 8:13:12 AM UTC-5, [e-mail] wrot e:

The question though is whether the blower motor is oversized.

I'm more familiar with commercial than residential. In commercial, vents a re often adjusted to balance air flow to the different areas. Some might b e fully open but most probably partial. Of course in commercial the blower is usually adjustable too.

At any rate, I'm not so sure closing a few vents adds enough restriction to the system to affect airflow. A dirty filter blocks the only place air sh ould be going through, but the supply has lots of outlets. Unless the blow er is barely keeping up, closing a few vents probably just slightly increas es flow in the others, and the thermostat maybe satisfies faster.

In the rooms you are not heating, the temperature differential between outs ide and in will be smaller, so you will lose less heat overall.

[Stormin Mormon]

Colder rooms means less heat loss. Which means money savings on heat.

That's my simple minded view.

[Stormin Mormon]

So, if the air leaking out of the back bedroom is colder since the vent is closed, you still need to put the same ammount of heat into the house?

[bob_villain]

If the heat vent is closed and the cold air return is not blocked...there will be negative air pressure in that room that will draw in some warm air. How much would be the question...

[Vic Smith]

It'll save money. The contractor is selling a mini-split system. Don't be fooled.

[DerbyDad03]

I think that the comment related to the cold air return is key. If the cold air return is not blocked, then the cold air from that room will lower the overall return air, requiring the furnace to heat it back up. It will also cause warm air from the rest of the house to be drawn in under the door, assuming that is the largest "leak" into the room.

In the one room that I have closed off, I also crafted cold air return covers from foam pads and then placed a heavy box in front to hold it in place. This allows me easily remove the vent covers when I want to heat the room. The room is above an unheated garage and gets pretty cold. I wouldn't want all that cold air sucked back into the furnace.

(I love those pads. My list of uses for them just keeps growing and growing.)

[DerbyDad03]

As others have said, you can save money by closing of a room or two. However, if you close the output vents, you should also block the cold air return.

If the cold air return is not blocked, then the cold air from that room will lower the overall return air, requiring the furnace to heat it back up. It will also cause warm air from the rest of the house to be drawn in under the door, assuming that is the largest "leak" into the room. If it doesn't come in under the door, it's going to come in from someplace, which might be from the outside.

[Micky]

No. It restricts airflow to some rooms but not to others. That is different. Here's a hint, Any time *any* one uses the adverb "simply", he's probably trying to buffalo you. Either he doesn't understand himself or he's trying to trick you. It took reading thousands of usenet posts to notiice this fact.

The things that are really simple you generally don't need to have explained to you and when you hear a simple explanation, it is obviously true on its face. When people say "simply" (and a synonym I forget) they are almost never talking about something simple.

Hopefully, they have been sized accordingly.

If there is already leakage, an increase in pressure of 20% would increase leakage by 20%. That's still only a little bit in most cases.

Yeah, but to do all that you have to buy whole new systems, his plural, not mine. That many more electroniccs and pressure systems to go bad. IIUC, the labor to replace a condensor etc. for a small system is as much or almost as much as for a whole-house system, and with 2 or 3 (or 4) systems, after the first few years, something will be breaking all the time.

I think it will save money, especially if those rooms have outside walls, as I'm sure the bedrooms do. More later.

[Stormin Mormon]

You know, I'd never really put the thought into words, but this sure does make sense. I'll let you know if I pick up on the synonym for simply.

[Arnie Goetchius]

Thanks for all of your comments. It looks like the next step is to block off the returns in the unheated rooms. I found a "Magnetic Vent Cover" here that I will try:

[trader_4]

I bought one of those and it was totally worthless. The magnet is so weak, the cover heavy, that it won't hold on.

[Unquestionably Confused]

That's simple. Bullshit!

[TimR]

Do you actually have returns in all rooms? I don't, I have one return in the hallway, and the room doors are undercut to allow air return.

If you do, where is your return filter?

At any rate, it doesn't really matter.

The heat loss in that room is less when the room is cold than when it is heated. So the return air you pull back has lost less heat with the supply ducts closed.

[DerbyDad03]

I have returns in all bedrooms, 2 in the living room and 1 in the family room.

The filter is "in" the furnace, right at the main return trunk where all returns meet.

[taxed and spent]

you have REGISTERS in each room.

[DerbyDad03]

Not true.