Using the “rated” or “max/maximum” BTU capacity when sizing a mini-split
michaelbluejay
| Posted in Green Products and Materials on
Here’s what I’m including in my article on HVAC sizing. I’m submitting it here for peer-review. Thoughts?
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Confusingly, equipment specs show both a “rated” BTU capacity as well as a “maximum” capacity. For example, a mini split I bought has a “rated” cooling capacity of 6000 BTU, and a “max” capacity of 11,184 BTU. Which figure do you use when matching the equipment to your Manual J?
The short answer is that you can use either, but in general I feel it’s better to match for max. [see details in the article linked below]
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So, after posting the above, I rewrote huge chunks of the article. I think there's more practical detail in my HVAC-sizing article than any other article on the same topic that I've seen. At the same time, I'm not infallible, so I hope some of you will check it out and share your thoughts, if I'm able to share the link and not have it rejected as spam: https://michaelbluejay.com/electricity/hvac-sizing.html
I know this is mostly link spam, but there is too many issues to leave it alone.
ManJ is very conservative, right sized equipment is already oversized, so using rated capacity will mean even further oversizing. For any sizing always use the max number.
The other thing is that chart. Except for a uninsulated pole barn, there is no livable house in cold climate that will have 40-60BTU/sqft heat loss. I've done fuel use based heat calcs on somewhat air slead uninsulated brick house in zone 5 and was 17btu/sqft. Some for the rest there:
https://www.energyvanguard.com/blog/air-conditioner-sizing-rules-of-thumb-must-die/