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Comment by SenHeng | Hacker News Reader

I'm in the middle of building a PassivHaus. The building itself is mostly done and we're working on the interior. There are still a few gaps that haven't been plugged and the heat exchangers have not yet been installed. I'm above 800m elevation, snowstorms every weekend. It's cold here. My house also actually faces West instead of South, so I'm not getting much heat from the sun. This was a surprise to use because the previous house on the same site had the same orientation and was scorching during the evenings, it's amazing what a pair of Low-E triple paned windows can do.

Despite all that, the builders manage to work inside the building with a single kerosene stove[0]. And the building stays comfortable for several hours even after the stove has been turned off.

[0]: https://nimmi.jp/kurashi-stove/

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I'm looking into making a house sustainable right now and the windows are actually a point of contention. One side thinks super-high insulated (triple pane) windows are a waste of money, the other swears by them. Assuming the frame doesn't leak, does triple really make that much of a difference?

As others have said, solutions depend on your climate, and especially on whether you principally have heating or cooling loads.

For cold climates, designers such as Thorstein Chlupp (Rienna LLC, in Fairbanks, AK) rely on triple-paned high emissivity windows for solar gain, and external thermal shutters at night to reduce radiative loss.

For warm climates, you'll want low emissivity glazing, as well as awnings or landscaping which block direct summer sun while admitting light. For winter time, you can probably get by with internal thermal curtains in winter, though an external storm glazing or shutter may also be helpful.

Having windows face the equator (that is, south-facing in the northern hemisphere, north-facing south of the equator) will increase light and decrease heat loss. Glazing on the pole-side of your home is generally reduced, and in sufficiently cold climates, eliminated.

More than you'd ever want to know (2h26m video) here:

https://yewtu.be/watch?v=Xen_VWyDezY

Yes. Makes measurable difference. Especially big picture windows. Other things to consider: is the type of glass. In places like Arizona you may not want sunlight to get through, but further north, the sun can provide a great deal of heat. So you want transmissivity. To stop that in the summer, you have a overhang roof, far enough out, to block sun in summer but not winter. Also, be smart installing the window, to prevent leakage around the frame, lots of good tricks there. For example- Avoid tightness of frame.

You must also be careful on how you mount the windows. Have a look at the german standard called "RAL montage" to see that you need an inner and outer membrane and then have a look on where to mount the window inside the wall.. the best solution is to mount it outside the wall in the insulation, the second best solution is to align it at the face of the wall.

Generaly speaking, yes, BUT the design needs to be taken into account.

A window (good as it might be) is "worse" than walls (besides being much more costly), the modern design trends are for extremely huge windows, that (whilst they give much more light, which expecially in northern climates is a wanted feature) are a problem, from a thermal viewpoint.

The typical size of windows in "normal" houses varies (depending on countries) like 1/8 to 1/12 of area of the floor of the room they are in, modern designs can be often 1/5 or 1/6, it is clear that the less amount of window surface you have the less relevant are its characteristics, and you have to consider also the effect of shutters or similar.

This depends on your house - heat tends to leak out through the lowest path of resistance so if you have a well-insulated house with leaky window, it would certainly be the case but without considering what the rest of the house is like, it would be impossible to tell how much they would help.

Heat leaks out through all path of resistance not just the lowest. (The lowest might dominate though if it is orders of magnitude lower than the second lowest)

Depends on your climate and the heat differential between inside and outside. Triple glazing is effectively double the R-value of double glazing, so in a cold climate yeah..

In the house I'm living in, which was built in a transition point between making sure houses don't leak and the realization that you then need active ventilation, I have the problem that the windows are not insulating enough, so I end up with water condense on the inside when it's freezing outside. If you are going to replace the windows, I would definitely buy triple-paned, unless you only have a small temperature difference.

Windows have a U or R value like insulation, so you can use that to compare.

We are currently building a house and the triple glazed windows we chose have a U value of 0.9. The same manufacturer also makes double glazed windows which have a U value of 1.3.

I’ve not had a chance to test it in summer yet but it’s still cold to the touch even in the evening sun so I guess that’s a good sign?

I went with Low E specifically because I’d rather be cold than hot and wanted to block out the scorch from the evening sun.

For us it did. Estimated 2 degree Celsius on the inside during winter already make a big difference in comfort and how you will use the space in front of the windows.

Windows, walls, ceilings and so on have to match of course, our house is overall well insulated.

yes, it's like wearing a sweater vs. wearing two sweaters

Get yourself a FLIR (the phone attached ones are not that expensive) and check for yourself. It is a great tool.

they are worth it in cold climates if you use fixed or very fancy casement windows with maintained seals. Double-hung will just leak around frames and sides.

Also ensure you use a good brand which will be around when you need a replacement and hope to get an actual match.

They can be a dream in terms of noise blocking as well.

How is the ventilation and air quality? I work in a passive house in and we're experiencing significant issues with the indoor air quality when the building HVAC turns low.

I wouldn’t know, they aren’t installed yet. Japan doesn’t really do central heating or ventilation so I’ve got 4 smaller air exchangers all over the house and they’re supposed to work together somehow?

For heating a home efficiently, one approach is a rocket mass heater. It does require burning firewood, but if that's an acceptable/desirable quality, this technology seems far more efficient than standard fireplaces.

https://en.wikipedia.org/wiki/Rocket_mass_heater

I have thought about that but it’s a bit too much custom work to add into a passive house.

I might try one in a future garden shed/office.

Is a stove like that not really dangerous in an air-tight house? Where do the fumes go?

Most air-tight houses have an integrated MVHR (mechanical ventilation with heat recovery) system, which is kind of the inverse of an HVAC setup. There's a constant small air current being moved through the house, and when it exhausts to the outside world a heat-exchanger captures as much heat as possible from the exiting air and uses it to heat the entering air. Airtightness means you can control where the air enters and exits, which means this trick is possible.

All that being said, I'd expect a permanently-installed stove to have a flue (which results in the stove technically being a leak, but that's solvable). I assume the kerosene stove mentioned above is in use while the house is incomplete, so not yet airtight.

Yeah, like fish said it’s not airtight yet so probably not that big of a deal.

Sounds great. Do you have a blog or anything online about your project?

Unfortunately no.

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