Questionable Advice from Fujitsu Tech Support Line
Hey folks-
I’m an old contractor building a new house- hopefully my last! I think I’ve decided on an HVAC system utilizing two separate, single-zone Fujitsu splits in a tight, well-insulated 1200 sf single-story home. I’m doing a self-install, since I can’t find a knowledgeable contractor out here in the sticks. Manual J says I’ve got 16400 BTU heat, and 17350 cooling in zone 3A with design temps of 21F and 94F, but I think my loads may be even less. I like the idea of using two separate systems that will avoid modulation issues and overcooling in small rooms.
A call to Fujitsu Tech Line was confusing. Tech said a 7K BTU slim ducted air handler and a 7K wall unit were “close enough”, for an 18K dual-zone system, but if I was using two single zone, 9K outdoor units, I should match two 9K BTU air handlers to them. Never got a reason why the difference, and not convinced I received good advice…
I’m thinking 9K is going to be too much, but I also don’t want incompatibility probs, and doubt we will be happy going with a single-zone for the entire house.
So- can I slightly undersize the indoor units relative to the outdoor units or should I just listen to the Fujitsu tech and match indoor and outdoor?
Opinions?
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Replies
With multi splits there is a tolerance for over under matching indoor/outdoor units. Maybe as wide as 70-130%.
But the min modulation will likely be lower with the 1:1 9k units even though their max output is higher.
Only reason to go with the multi split would be to get a base pan heater if that’s important to you. Otherwise the 1:1 9k will outperform is basically every metric.
The 9k, 12k, and 18k Fujitsu slim duct units all have the same minimum outputs. If modulation is your concern could you not go with a single larger unit?
> can I slightly undersize the indoor units relative to the outdoor units
What do you expect to gain by this?
> should match two 9K BTU air handlers
I didn't follow this either - you think that 2x9K = 18K is excessively oversized for a 17,350 Manual J?
Do review the latent performance at low loads (almost always a major mini-split weak point).