Manual J Heat load of a house has a multiple of (1.7) * (house BTU usage)?

by jdl   Last Updated October 10, 2019 02:21 AM - source

Is this correct?

So my 33,000 BTU house, via measurements, appliances, people,... we now...
- multiply by 1.1 (Duct loss/gain factor)
- multiply by 1.3 (Moisture Removal) ...odd... larger systems don't pull out moisture
- multiply by 1.2 (BTUH x 1.2 factor)
yields a multiplying my 33,000 x 1.7 yielding 57,000 BTU 
     or divide by 12k and get 4.8 TON HVAC.

My house originally came with 3.5 ton hvac which matches well with the 33kBTU x 25% more for heat loss. The excess humidity was pulled out and felt comfortable and breathed well.

Contractors say, via manual J Heat load, that we need a 5 TON Hvac. Well the 5 ton unit doesn't remove the humidity, it seems to build it up. We have to open doors and windows over night to get ride of the humidity.

(Home at NIGHT, with doors and windows open)  RH:  40% -> 33% 
(Home during DAY, with doors and windows closed)  RH:  33% -> 40% 

**Note, outside humidity is 10% at 95F during the day.

Tags : hvac

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