mini split ?

[EVOLVO]

What is the best way to use a mini split for heating my house? Should it be left at a preset temp 24/7, or should it be turned down at night and up during the day. Which way is the most efficient?

 

[theoldwizard1]

First, a mini-split is not the best solution for HVAC in a typical US house. Putting air handlers in each room can quickly get very expensive. Plus the mini-splits that can handle multiple air handlers are less efficient than the one that can only handle 1 air handler.

The answer to your question depends on a lot of things. First, is personal comfort. Some people LIKE to sleep in a colder room. Second, is how much insulation you have or how fast your house loses heat.

The short answer is, turning it down at night will save some money.

 

[EVOLVO]

Ok, thanx. A bit more info. We're in the PNW so winters are pretty moderate. The house was built in 2000 with 2X6 walls and good inso, it seems to be pretty airtight. We're looking at a Fujitsu, the salesman (!) says he can heat our whole 1800 sq ft two story with one air handler (18000 btu, I'm not sure of that). His theory is if you leave it on 24/7 it will be more efficient because once the house is up to temp the unit won't have to work as hard to maintain it there, thereby saving $$$. But as you guessed my wife likes a cooler night time temp. We have high efficiency propane forced air now. I guess if we choose to cycle the mini we could fire the propane to take the chill off and than turn it over to the mini.

 

[tyme2par4]

The short answer is, turning it down at night will save some money.

To an extent. With a furnace, you can set it back 10 degrees at night, and in the morning it will fire up and bring the house up to temp quickly.
With a mini split, you really only want to set it back a couple degrees. Setting it back farther will cause it to work hard getting the temp up, and unless it's oversized, it will take a lot longer than a furnace to warm up.

We're looking at a Fujitsu, the salesman (!) says he can heat our whole 1800 sq ft two story with one air handler (18000 btu, I'm not sure of that). His theory is if you leave it on 24/7 it will be more efficient because once the house is up to temp the unit won't have to work as hard to maintain it there, thereby saving $$$..

Fat chance of conditioning 2 floors with a single head. They will never stay anywhere near the same temp. Not to mention if you have any interior walls...
I had a 15k BTU Mitsubishi in my previous house (2000 sqft colonial). That did a decent job of keeping the first floor comfortable, but there was virtually zero effect on the temp upstairs. And on colder days, the rooms farther from the head were noticeably cooler.

Also, personally I would go with Daikin or Mitsubishi over Fujitsu any day. I have a Fujitsu in my current house. They are cheaper, but I hate the fact that you only have 2 degree steps for temp settings. Also I feel like they don't circulate the air well enough, so it's only the right temp near the head.

 

[EVOLVO]

I was pretty stunned when he told me that. I told him if I wasn't happy I wanted another one installed for free, he said he'd do it at cost (fat chance of that). OK so here's the real deal. Besides our house we have a rental cottage and rental house nearby. I had the Mitsu guy come give us an estimate on all three at once. I can't remember how many units he wanted to do but I do remember he said, gulp $40,000 The Fujitsu guy came in 75% under that @ $10,000. But because wifey likes to sleep cool we only did the rentals. He put one 12,000 btu head in each. The cottage is only 750 sf, the other is about 1800sf but is pretty wide open. They seem to be working pretty well, no complaints from the renters and this only cost $6000 + we got an $800 rebate from the PUD on one unit for getting rid of the electric forced air. Anyway we sleep upstairs so the cooler temps up there might be acceptable.
The Fujitsu's we have can be adjusted in 1* steps and has a swing mode on the directional vanes. I can feel the air moving when I stand in the doorway between the living room and kitchen, about 15-18 feet away so sounds like they have addressed the issues you had.
Thanx for your reply!

 

[justinjoyal]

Conditionning a 2-story house with a single air handler is tricky and never perfect but it can work rather well in some cases.

A few degrees stepback is fine but recovery is not as quick with a mini-split (gets longer the colder it is outside.)

Sometimes trickier in A/C mode because humidity control can become an issue.