Pros and cons, if any, of Low-E glass in pilothouse

[Geoff S.]

Ahoy All!

Long time, no post. Pointy head-scratcher du jour: I'm ordering new custom tempered glass for my trad ketch's center cockpit pilothouse. I'm being given the option of "Low-E" glass for an extra fee. I'm familiar with the replacement window salesman sales-pitch on the subject...but would it do me much/any good in a boat's pilothouse? I asked if there was any coloration to it (thinking ahead to judging nav light colors at night), and the glassmaker said no, but that "at some angles I might see a mirror image"...not sure I like the sound of that.

Given she'll be headquartered in Trinidad for the next buncha years, if there isn't any major optical trade-off and the "Low-E" treatment does actually deflect some UV, I can see some possible benefit in improved comfort and less damage to the woodwork inside the pilothouse...but then again, I intend to rig acres of sunbrella over her so I can walk on her decks anyway...so maybe moot?

Glad for anybody's dos centavos...

Geoff

[Bash]

Welcome back.

Low-E is a coating. It will dim the visibility slightly at night, but certainly not as much as having the glass tinted. It will significantly reduce heat in the pilot house, and will also protect the woodwork. It should only add about 10% to the cost of the job. For me, it would be a worthwhile expenditure.

[Pblais]

I agree with Bash. We have it in all the windows in the house and it does help on heat as well as when running A/C. Coating technology offers a lot of performance with just an up front cost and no maintenance. You don't get that on a boat very often. My dodger is tempered glass and it's nice but Low E for that wouldn't get me anything. On a pilot house it could be a blessing!

[Cheechako]

I have it in my house. It looks alot like a light gold coating.... you can see it when it goes bad! I have had 3 out of 12 windows go bad, then it becomes blotchy gold spots. It might help if your pilot house is enclosed, but my west facing house is hot anyway in the summer sun.... not sure the risk is worth the reward..... If they are a lot of work puting in I vote no due to risk of failure....

[sailorchic34]

In a house Low E glass does cut down on heat loss/ heat gain compared to regular glass. In California its pretty much required to meet title 24 heat loss requirements now a days in new construction.

A boat on the other hand has a whole lot less insulation, if any, in the cabin sides and top. So I see it being less helpful. Will it help, sure. But the extra cost may not be worth it. It is a coating as others have mentioned.. and sometimes fails.

Maybe compromise and use regular glass on the forward facing glass, so less reflection at night underway.

[LakeSuperior]

I think low emissivity (low e) glass would be a mistake in a Caribbean type warm marine environment. Low e works in the 3-5 and 8-14 thermal radiation tranmittance bands. Consider in the marine environment that the water temperature and sky temperature are normally colder than the air temperature. Therefore, the objective is to radiate heat to the cooler environment.

True low e does not block or retard the transmittance of solar radiation which peaks between 400 and 70 nanometer wavelengths.

Consequently, solar radiation will enter your pilot house and heat up the contents. The contents will re-radiate the heat in the 3-5 and 8-14 micrometer bands. If the low e coating is on the inside of the window the heat will be reflected back into the pilot house keeping it warmer.

If the coating is on the outside of the glass the radiant heat will be absorbed by the glass and heat up. The heated glass will not be able to radiate to the colder environment because of the low e glass. The glass will stay warmer and radiate more heat back into the pilot house.

If you are in a cold environment then low e glass would be of some benefit.