DIY mini-split across 3 zones. Was it worth it? Two years of load data.

Installed a Mitsubishi MXZ-3C24NAHZ2 multi-zone system (24,000 BTU outdoor unit) with three 9,000 BTU indoor units myself two years ago. This is not a quick project — I logged about 40 hours of work over three weekends — but it's been completely reliable and the performance has exceeded what I expected.

Why mini-splits made sense for my situation
My house has no ductwork. Previous heat source was propane forced-air (with its own air handler in the crawlspace). Adding central ducting to the house would have cost $12,000–18,000 according to three HVAC quotes. The mini-split system I installed cost $3,800 in equipment and maybe $400 in materials (line sets, disconnect boxes, conduit, mounting hardware). It heats better, cools better, and cost $14,000 less.

What DIY means for a mini-split
The compressor and refrigerant lines in a pre-charged DIY system (like the Mr. Cool DIY series) are factory pre-charged — no EPA 608 certification needed, no recovery equipment, no vacuum pump for the refrigerant lines if you use a pre-charged unit. However, Mitsubishi, Daikin, and other commercial-grade units are NOT pre-charged. They require:

• A vacuum pump to evacuate the line set before opening the refrigerant valves
• A micron gauge to verify the line set holds vacuum
• The refrigerant is already in the outdoor unit; you're pulling vacuum on the lines and indoor coils, then opening valves to flood them

I used a two-stage vacuum pump ($120 refurbished) and a digital micron gauge ($65). The vacuum procedure takes about 45 minutes per zone. If the lines don't pull to below 500 microns and hold for 30 minutes, there's a leak to find and fix before opening the refrigerant valves.

Performance at cold temperatures
The Hyper-Heat designation on Mitsubishi's H2i series means rated heating down to -13°F (-25°C). My actual experience: at -10°F the system heats adequately but you can feel it working harder — the defrost cycles are more frequent (maybe every 40 minutes versus every 90 minutes at 20°F) and the discharge temperature is lower. I added baseboard electric resistance heaters in two rooms as emergency backup, which have run a total of about 8 hours in two Idaho winters. The mini-splits handle 95% of heating demand.

At summer temperatures my garage zone cools to 68°F from 95°F outdoor in about 35 minutes. The SEER ratings are real in my experience — my annual electricity for HVAC (heat + cool) is about 2,400 kWh for a 1,600 sq ft house, versus ~900 therms of propane previously ($1,800/year at $2.00/therm). My HVAC electricity cost is about $264/year at my rate. Net savings: ~$1,536/year.

What I'd flag for first-timers
The line set penetration through exterior walls is the fussiest part. You're drilling a 3-inch core hole, routing refrigerant lines + communication wire + condensate drain + electrical in a single sleeve, sealing around it against air infiltration and pests, and keeping the line set slope consistent so condensate drains properly. Plan this carefully before cutting. A slightly wrong hole location is painful to fix after the fact.

The communication wire (the multi-conductor signal cable between indoor and outdoor units) is often the source of commissioning errors. Mitsubishi uses a 3-wire S-Bus communication protocol. Polarity matters. If the indoor unit displays a communication fault, this wire is the first thing to check.

Permits: mini-split installation requires a permit in most jurisdictions. The electrical connection (240V 20A or 30A circuit per outdoor unit) definitely requires a permit. Some jurisdictions also require a refrigeration mechanic license for the refrigerant handling even on pre-charged lines. Check locally before you start.