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Old 03-11-16, 09:31 AM   #5
gtojohn
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I agree, manual j can be off quite a bit. Our design temp here is 96F however in the past ten years we have long stints of 100f+ days. One year we had over 60 days straight of triple digits. HVACs sized too close to manual J couldn't keep up. Lots of unhappy customers. Heating obviously you need to plan for those extremes as well, just because you average 40f for a low doesn't mean you won't have a freak 20f week. Perhaps a good argument for multistage equipment that could ramp up when you need it.
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