Pretty much. Assuming your system is properly balanced in the first place, you can close a small portion of the vents without screwing anything up too much, but A) that's a big assumption, and B) most houses only actually have 6 or 7 vents, so closing 2 is enough to throw it off quite a bit.
That being said, if you're reading this, CHANGE YOUR FURNACE FILTER, people! All those case-quantities of Filtrete that we keep buying because they're unspeakably cheap? Use 'em! Change it every month or two.
Many furnaces are two stage or variable burner so only run 100% on the coldest days if properly sized. In my house due to large open stairways I have to close vents on a given floor depending on the season or it over heats or cools one of them. Did that with my old single stage 92% eff furnace for decades with no problems. I recently replaced it just because my A/C crapped out with a 96% one. Furnaces have temperature sensors to prevent overheating the exchangers. As always just cause you saw something on the internet doesn't make it true. Not saying this auto vent is a good idea or not but it obviously blocks some of the airflow when open so will reduce what can be delivered to the room.
A lifetime ago I did HVAC installation for new buildings. Some of the ideas presented are true but not as much as suggested. I'd go as far as closing 30% of the vents but no more than that.
There's no particular balancing factor beyond what is naturally occurring. The BTU of the furnace is calculated based on square footage and climate, and # of vents based on room size and location. Same size furnace may have more or fewer vents in a particular installation and flow rate through them depends on the building layout and furnace location.
It is true that if too many vents are closed it will negatively effect burner and motor heat buildup, but there's plenty of margin to close a few vents. The more common reason to do it isn't to save power though, it's that distant rooms with more bends in the ducts tend to receive less airflow so when you set the thermostat to a temperature then you go room to room and close vents the amount needed to get the coldest room to reach the thermostat setting and the rest to a flow rate that matches that. Otherwise you have to add assist blowers or in-duct dampers that add to cost or noise and you may still need to adjust room vents.
I was about to add a comment but then noticed that dave_c got it right. More interesting problems occur with central AC systems where duct resistance, filter size, MERV ratings and supply vent closing all affect flow rate over the coils. The latter usually must be at least 400 ft3/min/ton of capacity. All air handler blowers are rated and the parameters within the tolerated resistance ranges provided by the manufacturers. This is also why it's a bad idea to use thin filters with high MERV ratings.
My thermostat has been on the fritz lately, so I've been regulating the house temperature by closing all of the vents, when necessary. Am I correct to understand that this is not a good idea?
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http://www.doityourself.com/forum/gas-oil-home-heating-furnaces/412840-closing-vents-unused-rooms-bad-ok.html#b
That being said, if you're reading this, CHANGE YOUR FURNACE FILTER, people! All those case-quantities of Filtrete that we keep buying because they're unspeakably cheap? Use 'em! Change it every month or two.
:D
There's no particular balancing factor beyond what is naturally occurring. The BTU of the furnace is calculated based on square footage and climate, and # of vents based on room size and location. Same size furnace may have more or fewer vents in a particular installation and flow rate through them depends on the building layout and furnace location.
It is true that if too many vents are closed it will negatively effect burner and motor heat buildup, but there's plenty of margin to close a few vents. The more common reason to do it isn't to save power though, it's that distant rooms with more bends in the ducts tend to receive less airflow so when you set the thermostat to a temperature then you go room to room and close vents the amount needed to get the coldest room to reach the thermostat setting and the rest to a flow rate that matches that. Otherwise you have to add assist blowers or in-duct dampers that add to cost or noise and you may still need to adjust room vents.
Thank you!