Hello, is there a way to install something like a "valve" inside the forced air heating duct branch that delivers heated air to rarely used areas in the house? I have tried to shut the vents on those walls, but it made the temperature just a bit lower, which was not enough. I am looking for something like cutting the duct and putting a manual shutter to block the flow whenever heat is not required.
Would appreciate any suggestion. Thanks, h.

Is there a return air duct in that area?

You can install a zone valve and thermostat and close off any return lines. You can also install a manual duct damper. You will still need to close off any return.

Is there a return air duct in that area?

No.

You can install a zone valve and thermostat and close off any return lines. You can also install a manual duct damper. You will still need to close off any return.

No, that area has no return duct.

Go to HD or Lowe's and buy a manual duct damper. It fits in line and seals off the duct. Depending on how many supply lines you have to the area, you may need to buy more then 1. They are about $10 or less. When you install it, a fairly easy DIY job, you turn the handle perpendicular to the duct to close and in line to allow flow.

How do you disconnect a duct? Mine is all wrapped in (modern foil) insulation so I can't just go look.
Does it just slide apart or is there a strap? Can a decrepit old lady do this?

How do you disconnect a duct? Mine is all wrapped in (modern foil) insulation so I can't just go look.
Does it just slide apart or is there a strap? Can a decrepit old lady do this?

There is a short stretch of the duct that is easyly accessible. I will probably cut it with a utility knife where I want to put a duct damper: it is a soft, flexible material. Then insert a short segment of same diameter pipe with a damper in it. The final plan depends though on what kinds of dampers are available at the store.

Sorry to butt in - I want to do this too - and most of my ducts are the big rectangular kind.

Sorry to butt in - I want to do this too - and most of my ducts are the big rectangular kind.

Dear decrepit old lady : in round metal ductwork you find a joint and install a sleeve with the damper or drill two holes opposite each other and install just the damper. Probably not possible with large rectangular ductwork. In flex duct it is easier.
Respectfully submitted :The decrepit old man.

Sorry to butt in - I want to do this too - and most of my ducts are the big rectangular kind.

Whatever duct you have it most probably is standard. Which may mean two things: the damper you want to install is available in HD or other plumbing shops (like, a sliding shutter screen or the one on the photo) or you may be able to replace a short rectangular segment with a round piece with a damper in it. I have seen round short metal duct pipes with a damper inside.

Thanks, both of you. I'm mostly concerned about how hard it is to take sections apart to retrofit, given that there is no flexibility.
I'm wondering if it makes sense to replace those big ducts with round flexible ducts and if that is more energy efficient anyway, and if the furnace fans can adjust to the change?

Just talking two rooms that are part of the biggest zone. (I might just stuff towels into the vents this winter, since the flaps don't close very well. But there is still plenty of warm air lost trying to get out.)

Well if this is not something you want to change very often you could;

Remove the registrar cover, lay some plastic over the hole, Put the registrar cover back in place, pushing the plastic inside the duct. Trim the excess plastic around the registrar.

This should almost completely seal the duct. If you want to open the duct, remove the registrar and throw away plastic.
Cheap and easy to do.