Porch sliding door and heat gain.

Dinarius

Not sure if this is the right forum.

We live in a standard, late 1950s, semi-detached.

It’s not warm in winter, despite having the walls injected and double-glazing installed throughout when we did it up about 12 years ago. We’re considering having it retrofitted, but cost is an issue.

Meanwhile, we’re thinking of sealing the porch with a sliding door. Are there any figures available on the gain to be made from doing this?

Thanks.

D.

10-10-20

Hi! Not so much heat-gain (unless it opens into the house), but it will reduce the heatloss by cutting down the air which escapes from in and around the front-door. Is the front door a newer type (Palladio or such) or older PVC or wood? Is it drafty?

Lumen

I've seen numbers bandied about like 80kWh/m2/y but you could probably calculate it yourself based on the specifics of your house.

For example, take a volume of hallways, stairs, landings, open plan rooms which are directly connected to the front door (e.g. 80sqm x 2.5m = 200m3).

Assume that half of that volume of air (100m3) gets dumped outside when you use the front door, and that you use the front door 10 times a day. That's 1000m3 of warm air lost per day.

Average temp differential indoors-outdoors is 12C (average day-night is 8C from memory) .

So over the course of a year you need to warm up 365000m3 of air by 12C.

Specific heat capacity of air is 1.2 kJ/m3/°C.

So that 365000x1.2x12=5,256,000kJ = 1460 kWh. That's your heat loss with no draught lobby.

If you use the draught lobby like an air lock you're going to save almost all of that.

Its far from a perfect calc because some of your heating is be provided by solar gain.

You could sanity check the "half volume of air lost" calculation by testing the temperature drop after you've used the front door, e.g. if outdoor temp is 8C and the temp drops from 20C to 14C in the hallways a couple of minutes after the door is closed then it's about right.

10-10-20

https://www.boards.ie/discussion/comment/121552935#Comment_121552935

Good job on the hypothetical maths, like it. 👍️

GreeBo

If you are using the front door a lot in winter then a porch will surely help (as long as you close the front door before opening the porch :))

However, I would be surprised if this is the main culprit for a cold house.

Whats your attic like? What depth of insulation and what type?

Is your house on a concrete slab or suspended wooden floors? I'll assume its suspended timber with multiple vents in the "crawl space". If so, how deep is the crawl space? Insulating and adding an air retarder layer here will likely make the biggest difference in my experience.

Do you feel draughts around the skirting board and sockets? If so thats a tell tale sign off too much air movement under the floor making its way into the house and washing out all your nice warm air.