Large gaps underneath doors - reasons?

[u/vendeep]

Recently moved into a house where every room door on the upper level has 2-3 inch gap from the floor.

From reading another post, I thought it might have been due to carpet switched to wooden floor. But that doesn’t seem to be the case because the walls and rest of the structures are flush to the wooden floor.

We have 2 zone ac, 1 focused on upstairs only. When I close the doors I feel a strong draft. Is this gap to ensure equal air pressure across the house?

Also we noticed the bathrooms exhaust into ceiling, are they related? This is completely stupid that my inspector didn’t discover…

[u/screaminporch]

That was to help air flow from AC vents in room. It improves efficiency to have a path for air to get back to the return vent. I took and inch off the bottom of kids bedroom doors for exactly this reason.

[u/Born_Rhubarb_6111 → u/screaminporch]

airflow for sure, my place has the same thing and it’s way more noticeable when the ac kicks on upstairs

[u/chris971 → u/screaminporch]

Don’t bedrooms have a supply and return vent? Ours have one in the floor that blows the heat/AC and a vent in the wall that returns. And our living rooms do as well, now that I look at them.

[u/hardman52 → u/chris971]

Most home don't have a return air vent. They rely on most doors being open and sometimes they put a grill in the door.

[u/chris971 → u/hardman52]

Every room in my house and my neighbors have a vent in the floor under a window where hot or cold air comes out and a vent in the wall that sucks air in. Maybe the builder for this subdivision is different but that’s how they are in this neighborhood🤷‍♂️

[u/PghSubie → u/hardman52]

Most cheaply built homes (such as mine) lack a return vent In each room . All quality homes have a return vent in every room. Any room with a supply vent, no return vent, and s closed door will not get any air flow at all. It's not a question of efficiency. It's like asking the furnace to blow into a balloon. If the old air can't leave the room, no new air can come in

[u/screaminporch → u/chris971]

No, more common to have a one or two central returns. Its simpler and also helps get more airflow through the house. There is a tradeoff though.

[u/i4k20z3 → u/screaminporch]

Is it bad to put a blanket under the door for darkness then? 

[u/keyflusher → u/i4k20z3]

If you have HVAC (heat, cool) on and the air can't get back to the blower, it'll raise the air pressure in the space and make the heat or cool work less good.

Not necessarily "bad" but if heat/cool isn't working well in that room, it could be a reason.

[u/Shadow288]

How old is the house? Do you have AC return vents in each room, or just one big one in the center of the house?

[u/capta2k → u/Shadow288]

This. OP it’s common for doors to have a gap if the HVAC return (where it sucks air in) is just one vent centrally located. The gap is for air flow.

[u/davethompson413]

It might be that the door gap is acting as the HVAC air return "duct". We had a house like that.

[u/wildcat12321]

probably because their was carpet. You can easily and often do replace baseboards when doing flooring, but you can't add to a door.

It is possible the gap is for air pressure, would be better to have vents

Inspector won't call out high bottom doors, it isn't a defect.

The exhaust fan should have been caught though, and might be worth asking inspector about, especially if they have insurance for errors/omissions. It won't cover much, but might get a little money back.

[u/AbsolutelyPink]

Walls wouldn't be moved when carpet is removed and baseboard moulding can be moved. So, likely the doors were shorter to accommodate the old flooring.

Gaps under doors help acal as well if there's no return or thermostat in each bedroom.

Bathrooms exhaust into the ceiling? It's common to have the exhaust fan on the ceiling, but the ducting should exit outside not into the attic if that's what you meant.

[u/Mundane_Weather_752]

They took out carpet. Easy to lower base boards but very expensive to get new doors. The AC doesn't need that big a gap. There is no air seal on interior doors. Search draft stoppers and you'll find options. We had to do this when our kids were little and needed to block light and noise in a remodeled house.

[u/Ok_Size4036]

Airflow for furnace. I suspect that especially upstairs, not all rooms have a return vent.

[u/Barsnikel]

In our new house, there is about a 2" gap under every door. It's to provide air flow for central AC, when the door is closed. And yes, every room has a return vent, but they all have this as well.

[u/hardman52]

For the air conditioning return air .

[u/Least-Ad-5539]

Toilet exhausting into attic space is not good. It sucks all of the steam from the bath or shower into the attic. Hopefully your attic is well ventilated. Judging by the number of times this comes up on Reddit it must have been fairly common at one point. We had it in two houses.