heavydawson Registered User
#1

We're at the planning phase of a new build. I'm interested in installing MHRV in conjunction with a ground source heat pump. We've got a 150mm cavity with standard 100mm blocks, and 150mm Xtratherm CavityTherm full fill boards.

Herself desperately wants sliding sash windows, so I'm concerned about air leakage. I won't mention the companys name here, but we're looking at sashes with the following rating:
Thermal Transmittance - 1.4W/m2.K
Solar Factor - 0.45W/m2.K
Effective Air Leakage - 0.01W/m2.K

I haven't been able to draw the conversion from effective air leakage in terms of Watts to air changes by volume.

Wondering if someone can help deciphering how to factor window air leakage into an estimation of how the windows will affect air changes?

#2

The effective air leakage rate of any one single item tells you very very little. I'm not saying it's not usefull - perhaps it's best use though is to compare one window with another.

Another way is to ask does the trade lit state the m3/h/m leakage rate , tested to BS 6375 -1 2009 ? Or does it state a Classification number according to this standard. This BS divides windows ( and external doors ) into 4 classifications 1 being the poorest , 4 being the best.

Even with this determine this you really can't zoom in on one aspect of a building to decide on air tightness/MVHR. The whole assembled building must be tested.

BryanF Moderator
#3

heavydawson said:
We're at the planning phase of a new build. I'm interested in installing MHRV in conjunction with a ground source heat pump. We've got a 150mm cavity with standard 100mm blocks, and 150mm Xtratherm CavityTherm full fill boards.

Herself desperately wants sliding sash windows, so I'm concerned about air leakage. I won't mention the companys name here, but we're looking at sashes with the following rating:
Thermal Transmittance - 1.4W/m2.K
Solar Factor - 0.45W/m2.K
Effective Air Leakage - 0.01W/m2.K

I haven't been able to draw the conversion from effective air leakage in terms of Watts to air changes by volume.

Wondering if someone can help deciphering how to factor window air leakage into an estimation of how the windows will affect air changes?

re air-tightness: ask to speak to previous cleints where an air-test has been carried out. or even better their A-T tester
the solar factor seems a bit low too,it may be worth asking the increase in cost to improve this

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