DIY Door Draft Guard $1.26 for 2 doors (63c ea)

I've used it on 2 interior doors. Probably wouldn't be so good for exterior. The foam will break down from exposure to the elements. You could give it a try, might have to replace it next year but it's not costing you much anyway.

mmyk72 said:   I wouldn't think an exterior door that only has a small leak would work. The foam would keep the door from closing against the bottom threshold altogether.

But if someone keeps the whole house on the cold side and heat up a room or two more, this is a great way to isolate those rooms.

I am one of those. Let me try this. I was infact thinking about isolating my master bed from rest of the house.

I can imagine this and the "real" one too probably can scratch up your floor once some dirt/debris get caught under it and dragging it back and forth. Good DIY idea though OP!

There are some basic things about home HVAC equipment you need to remember. The heated/cooled air, leaving your furnace via floor (ceiling, whatever) registers is not going to disappear – it has to go back to the return grille in the same amount. There only 2 valid cases to use these draft guards: to block draft under your entry doors and/or to block draft under the doors to the rooms that have air dampers installed in their air supply lines, so there is no air from HVAC coming into them (regular registers in a closed position are not a suitable alternative to an air dumper).
Otherwise, you are creating a negative pressure in your house, with some rooms “over pressurized”. That’s why the most ideal scenario when every room with air registers has to have a return grille located across from it. Usually, it never the case, there is a central air return with a dirty air filter, additionally blocking the air flow, so all the inside door are REQUIRED to have an opening under them (gap), and it is actually regulated. With no gap, the system is going to suck the missing air from outside the building envelope, or, if it is an extremely sealed tight construction, you will be creating a situation in your air handler when it is “air starved”. Booth of the situations are bad for your HVAC system and for your wallet.

omarECD said:   How do you keep the foam in place? I imagine it's going to move around from the friction against the floor.All I can say is it stays put on solid floors (hardwood, tile). Might shift on carpet, dunno. If the gap between the door & floor is too small there may be an issue, but the standard gap seems to match the 1" foam pipe insulator well.

77Rus said:   There are some basic things about home HVAC equipment you need to remember. The heated/cooled air, leaving your furnace via floor (ceiling, whatever) registers is not going to disappear – it has to go back to the return grille in the same amount.
...
Agreed, those are good points. I use one on a door to the mudroom where the washer/dryer live. It's not the garage, though it's adjacent. The mudroom is inherently leaky because of the drip lines leading outside so it's important to keep that room sealed off.

Another is on a door leading to a leaky bathroom. The vent fan allows exterior air in and gets frigid in the winter. I'll be sealing that vent duct with a Battic Door when the weather becomes more bearable, but for now sealing & shutting the door helps. I can see how if every room were sealed off it would cause a problem for the HVAC, but if it's one room (or a small % of rooms in a large house), the other airways would compensate and have more airflow. Is that not true?
Also keep in mind that this doesn't seal the door 100%. If you want some air to continue flowing, you can cut it shorter so it doesn't fill the entire bottom surface of the door.

Remember when mobile homes used to have a 2 inch gap under all the interior doors, that was for he return air to the furnace. I know lots of people that keep the door closed to a bedroom to "keep the heat in". The room stays chilly because the heated air can't get in unless the cold air can get out.

77Rus said:   There are some basic things about home HVAC equipment you need to remember. The heated/cooled air, leaving your furnace via floor (ceiling, whatever) registers is not going to disappear – it has to go back to the return grille in the same amount. There only 2 valid cases to use these draft guards: to block draft under your entry doors and/or to block draft under the doors to the rooms that have air dampers installed in their air supply lines, so there is no air from HVAC coming into them (regular registers in a closed position are not a suitable alternative to an air dumper).
Otherwise, you are creating a negative pressure in your house, with some rooms “over pressurized”. That’s why the most ideal scenario when every room with air registers has to have a return grille located across from it. Usually, it never the case, there is a central air return with a dirty air filter, additionally blocking the air flow, so all the inside door are REQUIRED to have an opening under them (gap), and it is actually regulated. With no gap, the system is going to suck the missing air from outside the building envelope, or, if it is an extremely sealed tight construction, you will be creating a situation in your air handler when it is “air starved”. Booth of the situations are bad for your HVAC system and for your wallet.

Appreciate the explanation and advice, 77RUS. And thanks Peas for posting because we have a sizable gap underneath our front door and your post would be an improvement to our current door guard

jimates said:   
And certain areas of the south they are still called "trailer houses"
Naa we call em semi stationary Meth labs

I just bought this from Lowe's today and it looks (and hopefully works) great!
Thanks OP.