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skeeter20 · Nov 16, 2013, 09:23 AM

If I close the heat registers in unused rooms, will I get more heat to the rooms in use?

smearcase · Nov 16, 2013, 10:29 AM

This is one opinion about that:
"MYTH: Closing off vents and registers will reduce your heating bill.
False. If you have a modern forced air heating system, the pressure load is balanced throughout the house. Blocking the vent will impact how the system inhales and exhales air; it can throw the system out of balance, causing it to have to work harder or possibly break down.

Also the most energy efficient practice you can do is to have heat evenly distributed throughout the house. Blocking vents in certain rooms will make those rooms colder. Because heat moves from greater concentrations to lesser concentrations, these colder rooms will draw heat from other rooms in the house, making the whole house feel colder and causing you to raise the thermostat. "
From: Tips - Home Energy Myths Debunked - Heating, Air Conditioning -Furnaces, Air Conditioner, Heat Pump - DE, PA, MD | Horizon Services Inc.

joypulv · Nov 16, 2013, 11:58 AM

I'm not sure I believe a lot of it.
I have closed 1 vent in 1 room I don't use, and 2 at the far end of the big room I spend most of my time in (which are also farthest from the furnace, and hence have the coolest air), and am very happy I did. The place heats up in 2 minutes and the furnace runs a lot less. The louvers let a fair amount of heat through anyway, but the fans are blowing most of the air through the vents I do have wide open.

The bit about cold rooms - of course heat seeks a way out, but it's doing that all the time anyway, heading for windows and doors and ceiling vents and anyplace that's colder!

I do think that any room with a return vent will be sending colder air back to the furnace, making more work.

But I'd like to see something based on science.

smearcase · Nov 16, 2013, 12:16 PM

I gave that same info to my wife who is the chief engineer for heating control in our house and she ain't buying it either. Maybe the HVAC experts will come along and give us the straight skinny.

joypulv · Nov 16, 2013, 12:29 PM

OK, I found out more - if you have a return duct in any room you close off it isn't a problem. It's the negative pressure in a closed off room that is sucking air in from all the wrong sources that is the problem. I have return ducts in each room.
You can install wall vents ('transfer grills' or 'jump ducts') to solve this, low on a wall. (Or cut 14" off the bottom of doors.)

Grady White · Nov 16, 2013, 09:12 PM

Joypulv,
I certainly hope that 14" was a typo. I don't know of a soul who would cut 14" off the bottom of the doors.

I do not advocate the closure of registers or return grills. Most duct systems are maginally sized at best & restriction of air flow can, & often does, cause the furnace to "cycle on limit". This means the furnace burner shuts off while the fan continues to run to cool off the overheated furnace. After the furnace cools to below the point where the high limit (a safety switch) will close the burner is allowed to fire again.

ma0641 · Nov 16, 2013, 09:33 PM

Assuming constant fan pressure and volume, you will get more airflow. However, you will also have more realized skin cooling due to the velocity increase. Then, as Grady indicated, you have reduced airflow back to the return and overheating can arise. The only time closing all the unused room doors works is with gravity space heaters, not air flow heaters.

joypulv · Nov 17, 2013, 02:46 AM

I thought the 14" sounded strange but it was on 3 different non-profit energy sites.
Im not sure what 'more realized skin cooling' means. The change in velocity isn't that noticeable, and I for one have very little skin showing in winter.

And what about the air return in each room?

Grady White · Nov 17, 2013, 09:26 PM

Joypulv,
The "more realized skin cooling" is a term used to explain the cooling effect of increased air movement across the skin. An example would be to be outside on a cold day with no wind vs. being outside at the same temperature on a windy day. For all practical purposes it's another term for wind chill.
The part about returns pulling air from the wrong sources is pure horse hockey. If air can't get into a room, all the return grills in the world aren't going to pull air out. If they did, they'd suck the walls in.

joypulv · Nov 18, 2013, 01:19 AM

I do know what skin cooling and wind chill are. We are talking WARM air here is what I mean.
The energy non-profit sites I read said that the furnace finds air sources elsewhere (around the furnace itself) if individual room returns are non-existent or have no air to return. I see no reason to disbelieve that.

Grady White · Nov 18, 2013, 04:16 PM

I realize we are talking about warm air. The point I was trying to make is the faster the air is moving, the more of a cooling effect one senses.
Furnaces will suck some air through unsealed joints in the ductwork, furnace blower doors, etc. but the amount is usually not worth the cost of having all the ducts sealed. If ducts run through unconditioned areas, they should be sealed & well insulated.