Air Inflitration: Double Hung vs Slider

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Air Inflitration: Double Hung vs Slider

#1 Post by zaphod » Wed Feb 06, 2013 12:06 pm

Would like to see some discussion on air infiltration comparing double hung to horizontal double sliders.

People have mentioned that DH have better AI numbers than HS. Why?

Is that for a given window size, where the DH would have a shorter sash-to-sash seal length compared to a slider in the same opening?

Given the same product line from the same manufacturer is there typically difference in the sealing package between the two?

If you have a square opening, where the DH and HS would have equal sash-to-sash length, would the AI be thee same (all other things equal)


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Re: Air Inflitration: Double Hung vs Slider

#2 Post by Randy » Wed Feb 06, 2013 12:14 pm

The differences are a result of the variance in sill type and weatherstripping use. Sliders typically jump up .05 - .07 cfm over the double hung.
Last edited by Randy on Wed Feb 06, 2013 1:28 pm, edited 1 time in total.

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Re: Air Inflitration: Double Hung vs Slider

#3 Post by HomeSealed » Wed Feb 06, 2013 12:26 pm

At the same size, a dh will have superior AI ratings to the equivalent SL except in very rare cases. It is really just in the way that the window is designed and operates including the sill and weatherstripping as randy mentioned. I don't know if there are tests to support it, but given that the meeting rail (where the two sashes meet) is one of the weak points of a unit in terms of tightness, I would say that it is certainly feasible that it would be a contributing factor given that fact that it is far longer on the slider as you pointed out. I also notice some difficulty in sealing the ends of the meeting rail on sliders as there is a somewhat awkward interface where the sash goes into the track of the frame. This area is given extra attention in product design, but will invariably end up being the leakiest point on the window in my experience.
That said, I often have people request a twin dh where the could otherwise get a SL because they perceive that it will be tighter, however it is important to keep in mind that you are doubling the leakage on two units compared to the one SL. It would not be accurate to merely double the published DH AI rating as that is merely an average, however you get the idea. Additional length in sash to frame interface= more area for potential leakage.

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Re: Air Inflitration: Double Hung vs Slider

#4 Post by Windows on Washington » Thu Feb 07, 2013 8:44 am


Not much to add here. Both the design (pocket in most cases) as well as the interlock and weatherstripping possibilities, will somewhat handicap the slider when it comes to final performance numbers.

There are some good ones on the market but as a general rule, they will be about as leakier as randy pointed out above.

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