Comments on: Do You Really Need That Much Window Area?

By: Gene DeJoannis

Gene DeJoannis — Mon, 21 Aug 2023 16:55:19 +0000

BTW, Mark, you are correct that the R-15 claim for the attic door insulated cover is bogus. Even a cover made of 2″ of polyisocyanurate is not R-15, and that is about the best you can get.

By: Gene DeJoannis

Gene DeJoannis — Mon, 21 Aug 2023 15:36:05 +0000

Mark K, Danny is correct that the air flow will help prevent condensation, but the point of putting heat supplies bellow windows was originally basic comfort. Even good windows will have a higher heat loss than walls and so the cool surface will create a downdraft that will be uncomfortable. The heat source below the window counter-acts the cool, denser air dropping to the floor and should reduce the draft problem. As far as condensation goes, the glass surface will be the coldest thing in the room, and if it gets below the indoor air dew point, you will have condensation. Multiple glass surfaces (storm windows, double or triple glazing) will raise the the inside surface temperature and reduce the chance of condensation, unless you raise the indoor humidity too high. Having a heat source below the windows raises the glass temperature and reduces the chance of condensation. So heat below windows improves comfort by reducing drafts AND the likelihood of condensation on the glass. Super-insulated walls, air-tight construction and triple-glazing (i.e. passive house methods) make these issues go away, and supply air from a central interior location works fine.

By: Stacy Long

Stacy Long — Mon, 21 Aug 2023 14:14:03 +0000

In reply to Mark Kennedy. If installed perfectly, this product provides an air barrier and reflective barrier. Most reflective insulation is known for the R value scam. If you include proper spacers, this might get you R8, but the material R value is no higher than 2 from the double bubbles. I'm not saying the product itself is a scam as it may help prevent extremely hot attics from transferring too much heat into your house, but the marketers are acting up again. As for question 1, it was allegedly needed to prevent mildew and excess condensation when everyone had crummy single pane windows, but I agree it is wasteful even as some are in my 1992 double wide with storm windows.

By: Danny Gough

Danny Gough — Mon, 21 Aug 2023 13:49:02 +0000

On the contrary Mark K. Moving air across a cold glazed surface will reduce the risk of condensation. Moreover, since surface temperatures substantially influence thermal comfort, warming the surface can somewhat offset the radiant heat transfer from the body. The same is true for summer,. Although poor performing windows and an improperly installed cooling system could accidentally produce condensation, I don’t recommend it.

By: Mark Kennedy

Mark Kennedy — Sun, 20 Aug 2023 15:27:59 +0000

Two things:

1. Why do HVAC persons put the supply register in front of the window where it; creates condensation, thus slowly destroying the glass to frame connection and imparts a good deal of the heating and or cooling to the outside world?

2. How can this product have an r-value of 15 if it is made of Aluminum, have people no shame?

https://www.amazon.com/SmartATTIC-Attic-Insulation-Cover-Aluminum/dp/B0896Y8BXB/ref=mp_s_a_1_17?crid=3EPM741CJPJZF&keywords=attic+stairs+insulation+cover&qid=1692544062&sprefix=attic+stair%2Caps%2C114&sr=8-17&ufe=app_do%3Aamzn1.fos.18630bbb-fcbb-42f8-9767-857e17e03685

Respectfully submitted.

By: BayouBro

BayouBro — Fri, 18 Aug 2023 02:29:36 +0000

In reply to RICHARD MACCREA.

I was referring to aluminum foil in windows.

https://www.fema.gov/blog/6-ways-stay-cool-extreme-heat
Insulate your house.
You can keep your house cooler by insulating it and covering your windows with drapes or shades. Use window reflectors such as aluminum foil-covered cardboard to reflect heat back outside.

Throwing out ideas
Exterior curtains – mostly for patios
Outdoor window shades i probably what I meant.

By: RICHARD MACCREA

RICHARD MACCREA — Wed, 16 Aug 2023 17:47:00 +0000

In reply to RICHARD MACCREA.

I feel dumb for my reply about aluminum foil. I think you were referring to reflective film. There are a few considerations:
1. Unless it has holes, it is also a vapor barrier. You would need to be sure this wouldn’t cause problems with the rest of your insulation vapor barrier systems.
2. Don’t install it where you spend more heating than cooling, or it will increase your energy costs. (Also true for light colored or reflective roofing)
3. I have seen recommendations that there be a ventilated air space on the hot side of the reflective barrier. That might not be easy to do. That air space can get very hot in some circumstances. Make sure that is considered.

By: RoyC

RoyC — Wed, 16 Aug 2023 17:36:56 +0000

In reply to Robert Adams. I agree with Robert's points on trees being more of a liability than a benefit and he didn't even mention dealing with leaves in the fall.

By: Paul Szymkiewicz

Paul Szymkiewicz — Tue, 15 Aug 2023 19:44:07 +0000

In reply to Paul Szymkiewicz.

All good points, Roy. I just don’t think trees are a problem, they are part of the solution. Windows, and their orientation, size, number, glazing type, fixed shading devices, as well as operable ones are a big part of it. Solar heat gain is mostly desirable in some climates and mostly unwelcome in others.

When designing a subdivision, I would think about solar access first (for PV and for passive gain), and that would be relatively easy to do. Then I’d add site features to help with east/west solar gain (if mostly unwelcome). The individual home designs would also need to play ball. For example, run most streets as close as possible to being parallel to east/west line, and if the houses are close enough (which in a lot of new subdivisions it can be as little as 10-15ft) most would shade one another from east and from west. Then you tinker with window placement, horizontal and vertical shading devices etc.

Finally, in the context of this particular blog, the answer to the question “Do you really need that much window area?” is, in my opinion, “it depends”, because “that much” is a moving target if we are considering performance (thermal comfort, energy, daylight, etc) based on climate.

Finally, I don’t see solar PV as being “pushed”. It’s there, available, cheaper than ever, just reach out and grab it. Every kW on your roof makes a difference.

By: Robert Adams

Robert Adams — Tue, 15 Aug 2023 19:17:07 +0000

Shade trees are a great idea at first… Then when you realize all the costs involved with having trees over the long run they will end up costing you far more than the energy they are saving you. When you look at just the tree trimming costs alone you will never recoup that in energy savings. Then the house damage that occurs from falling branches etc. And then when the tree gets old enough or it dies or is damaged in a storm that tree can cost thousands to have removed.
We have many large oak trees and the do provide shade in the morning and the late evening but during the hottest part of the day they are useless as they don’t shade the house much at all. I would never have large trees near a house ever again as the liability they cause isn’t worth the miniscule energy savings.

As for shading windows there are external shade screens that are pretty popular here in TX and other places out west where it gets hot and stays hot for months on end IE 100*-110* for 7-9 hours a day. You won’t see that stuff as much in the *south* IE GA and other more northern states as it doesn’t get very hot there and not for very long the few days a year it does get hot.