In our condominium community we have a rule requiring the main doors to be kept closed in the winter because our homes are heated by natural gas, for which we each pay in our condo fees (no individual metering, as it would be too costly to install meters).
Some scofflaws leave their main doors open anyway, and one jerk insists that his solid-glass screen door keeps in the heat. I’d like to find an authoritative link to convince others who might be persuaded to revoke the rule. Does anyone know of one?
TLDR version:
Closed single-pane glass door won’t insulate much, but will lessen convective heat loss.
Closed double-pane and/or gas-filled glass door will both insulate and lessen convective heat loss.
An open door will do neither, and will let a lot of heat escape.
Longer version:
What is a solid glass “screen” door? I thought “screen” implied a mesh of some sort to keep out insects yet let in air, whereas solid glass implies no airflow.
Anyway, if it’s a solid glass door (and not a screen), it depends on the particular construction of that door. Newer glass doors that are double-paned and/or gas-filled can be effective insulators, but older-style single-paned glass doors that just have a single piece of glass are terrible insulation.
This is measured using something called U-factor, and if the apartment is relatively new you might be able to look up the door model in a window/door insulation database (US-based). Otherwise you can assume that double-paned glass provides a moderate level of insulation (similar to a wood door) and single-paned glass almost nothing.
However, even without the direct insulation, an open door will cause convective heat loss from the hot air escaping your condo. This should be obvious to anybody with a modicum of common sense – the hot air mingles with the cold, kinda like leaving a refrigerator open – but there are fancy formulas that describe it too.
We have a double pane storm/screen door. It’s just like a window. We often leave the wooden door open and enjoy the sunlight. There are no cold drafts if its installed correctly.
“Jerk”, eh? Guess we know what side of the argument you’re on.
The glass door is acting like a big patio window, which means that it’s less insulative than keeping the door shut, but it’s not like he’s letting the arctic gales roar through his house. However this assumes that the seals and weatherstripping on the screen door are in good shape and there’s not any air leakage.
Is he wasting heat? Yeah, a bit. Is it enough to get the condo board bent out of shape? Eh, probably not, unless he simultaneously cranks the heat in his condo to 90. He could, for example, actually be one of those people who likes keeping his place cool in winter and keeps his thermostat at 65 which means that he’s using a lot less energy than the biddy in 3A who does keep the thermostat at 75 all winter.
It seems like the best way to resolve this, or at least a good way, would be to get a FLIR camera (I think Home Depot might even have them) and take some pictures of your house with the door closed. Then open the door, leave it open for an hour (to let the glass ‘screen door’ warm up) and take more pictures. The FLIR camera will give you a good idea of how much warmer the screen door gets with the interior door open. Maybe it heats right up to room temperature. Maybe the interior door is junk and it was already that warm. Maybe the insulation in your condo is crap and you’ll find that out.
But, FTR, there’s really no question that a glass door PLUS an air gap PLUS an interior door is better then just the glass exterior door. Just stand next to the exterior without shoes on in the middle of winter and tell me your feet don’t get cold after a few minutes.
If the door faces south and gets sunlight, It is likely that the apartment gets more heat than it loses on a sunny day.
(After reading this I realized that despite saying this like I knew what I was talking about, I am really not sure. I think that it is true).
The condo I live in has individual heating, and I wouldn’t have it any other way. While there is certainly some “heating of your neighbors” going on, I can’t imagine that it would be significant in a modern building. I can guarantee that the fuel usage for a building such as the OP describes would be significantly greater than for individually heated units. There is no incentive not to have the heat on high all the time.
Can’t directly answer w/o a more precise description of what you mean by; standard glass outer doors, main doors and solid-glass screen door and how they are installed in your given situation.
If the glass door has a low insulation value it will still hold in heat because the only way for heat to get to the outside will be through the door by conduction, that is traveling through the door itself. But with the door open warm air will travel out the top of the door way and cold air will enter the condo throught the bottom of the open doorway.