What matters most for a mini split in a mixed climate?
Short answer: That it heats and cools about equally well. From New Jersey to Oklahoma, a mini split runs 967 to 1,583 cooling hours and 1,681 to 2,346 heating hours a year (ENERGY STAR), so it is the air conditioner in summer and the main heat in winter. The coldest design day in these cities is 6.8°F in St. Louis, inside what the MRCOOL DIY series heat at (down to −12°F and −13°F). The coldest night of the last ten winters was −17°F in Wichita, colder than that, so keep a backup heat source for the coldest nights. For the lowest bill across both seasons, pick DIY 5th Gen.
This guide covers Delaware and compares it with the other mixed-climate states, from New Jersey to Arkansas. Those states also have their own page.
Mixed-climate states compared
These states have real summers and real winters. The table shows the numbers HVAC sizing uses for their main cities.
| State | City (climate zone) | Summer high | Winter low | Cooling hours | Heating hours |
|---|---|---|---|---|---|
| New Jersey | Newark (4A) | 91.1°F | 12.1°F | 1,007 | 2,340 |
| Delaware | Wilmington (4A) | 89.5°F | 12.8°F | 1,015 | 2,346 |
| Delaware | Dover (4A) | 90°F | 13.9°F | – | – |
| Maryland | Baltimore (4A) | 91.3°F | 13.5°F | 1,050 | 2,172 |
| Virginia | Richmond (4A) | 92.4°F | 17.4°F | 1,188 | 1,980 |
| West Virginia | Charleston (4A) | 88.8°F | 9.6°F | 967 | 2,088 |
| Kentucky | Louisville (4A) | 91.7°F | 10.2°F | 1,150 | 1,975 |
| Tennessee | Nashville (3A) | 92.3°F | 14.9°F | 1,375 | 1,768 |
| North Carolina | Charlotte (3A) | 91.9°F | 21°F | 1,325 | 1,865 |
| Missouri | St. Louis (4A) | 93.5°F | 6.8°F | 1,215 | 2,009 |
| Kansas | Wichita (4A) | 97.3°F | 7.9°F | 1,225 | 1,981 |
| Oklahoma | Oklahoma City (3A) | 97.6°F | 14.6°F | 1,436 | 1,724 |
| Arkansas | Little Rock (3A) | 95.6°F | 20.1°F | 1,583 | 1,681 |
Design temperatures: ASHRAE 2021 (1% cooling, 99.6% heating dry bulb). Climate zones: 2021 IECC by county (PNNL guide). Hours: ENERGY STAR heat pump savings calculator (full-load hours; – means the city is not in its table).
One system for both seasons
In a mixed climate the same mini split cools all summer and heats all winter. The inverter runs at partial speed most of the year, which is where the efficiency comes from.
Which system for a mixed climate
What size for your room
Measure each room (length × width) and match it to an indoor unit.
| Room size | Indoor unit | Single zone voltage |
|---|---|---|
| Up to 250 sq ft | 6K BTU (multi-zone only) | – |
| 251–400 sq ft | 9K BTU | 115V |
| 401–550 sq ft | 12K BTU | 115V |
| 551–800 sq ft | 18K BTU | 230V |
| 801–1,050 sq ft | 24K BTU | 230V |
| 1,051–1,550 sq ft | 36K BTU | 230V |
Go one size up for rooms with west or south windows, a top floor under the roof, high ceilings, poor insulation, or a kitchen. A garage that isn’t insulated also goes one size up. Full sizing guide
Several rooms? See multi-zone systems
What it costs to run
Yearly cost to heat and cool one 12K room, at each state’s average power price.
| City | Power price | DIY Select | DIY EasyPro | DIY 5th Gen |
|---|---|---|---|---|
| Newark, New Jersey | 24.6¢ | $938 | $896 | $804 |
| Wilmington, Delaware | 18.7¢ | $715 | $683 | $613 |
| Baltimore, Maryland | 21.4¢ | $774 | $738 | $662 |
| Richmond, Virginia | 17.6¢ | $609 | $580 | $518 |
| Charleston, West Virginia | 16.3¢ | $562 | $536 | $481 |
| Louisville, Kentucky | 13.8¢ | $472 | $449 | $402 |
| Nashville, Tennessee | 13.4¢ | $443 | $420 | $373 |
| Charlotte, North Carolina | 14.9¢ | $508 | $482 | $429 |
| St. Louis, Missouri | 16.0¢ | $563 | $535 | $478 |
| Wichita, Kansas | 15.5¢ | $539 | $512 | $457 |
| Oklahoma City, Oklahoma | 14.8¢ | $487 | $461 | $409 |
| Little Rock, Arkansas | 14.4¢ | $478 | $452 | $400 |
Estimate, not a quote: (cooling BTU × cooling hours ÷ SEER2 + heating BTU × heating hours ÷ HSPF2) ÷ 1,000 × price. HSPF2 is the standard rating (Region IV) shown on the product pages. Hours: ENERGY STAR heat pump savings calculator. Power price: EIA, August 2026.
What the equipment costs
Prices for complete single zone systems: outdoor unit, indoor unit, pre-charged line set and remote. Shipping is free to all 12 states in this guide.
| Size | DIY Select | DIY EasyPro | DIY 5th Gen |
|---|---|---|---|
| 9K | $1,249 | $1,487 | $2,329 |
| 12K | $1,399 | $1,599 | $2,359 |
| 18K | $1,690 | $1,806 | $2,909 |
| 24K | $1,899 | $2,109 | $3,329 |
| 36K | – | – | $3,769 |
Rebates by state
Utilities with rebates on MRCOOL DIY models, from MRCOOL’s rebate data. Rebates checked November 2026. Amounts change; confirm with your utility.
| State | Utilities with rebates | Highest | Who installs |
|---|---|---|---|
| New Jersey | 3 | $12,000 | All need a participating contractor |
| Delaware | 2 | $3,000 | 1 of 2 need a participating contractor |
| Maryland | 3 | $1,700 | All need a participating contractor |
| Virginia | 1 | $400 | All need a participating contractor |
| West Virginia | None listed | – | – |
| Kentucky | 4 | $1,000 | 1 of 4 need a participating contractor |
| Tennessee | None listed | – | – |
| North Carolina | 2 | $2,100 | All need a participating contractor |
| Missouri | 1 | $1,200 | No contractor rule listed |
| Kansas | 2 | $783 | 1 of 2 need a participating contractor |
| Oklahoma | 1 | $600 | All need a participating contractor |
| Arkansas | 1 | $2,350 | All need a participating contractor |
Delaware
| Utility | Up to | Who installs |
|---|---|---|
| Delaware Electric Cooperative | $3,000 | No contractor rule listed, confirm with your utility |
| Energize Delaware | $2,125 | Needs a participating contractor |
DIY or a pro
MRCOOL DIY systems are built for a homeowner install: the line set comes pre-charged and connects by hand, so there’s no vacuum pump or refrigerant work. Most people hire an electrician for the new circuit, and permit rules depend on your city. Can you install a mini split yourself?
Which MRCOOL system for a mixed climate
Mini split questions for mixed climates
Is a mini split worth it in a mixed climate?
For most homes, yes: the same system cools all summer and heats all winter, so it replaces both a window AC and a space heater.
Will it heat on the coldest nights?
DIY Select heats down to −12°F and DIY EasyPro and DIY 5th Gen down to −13°F. The coldest night of the last ten winters was −17°F in Wichita, so keep a backup heat source for nights like that.
Does Delaware have its own page?
Delaware is covered here. Its numbers are in the tables above, and its rebates are below.
Are there rebates?
Some utilities list rebates for MRCOOL DIY models; see the tables. Many need a participating contractor. The federal 25C tax credit ended for systems installed after December 31, 2025.
How long does shipping take?
Verified orders ship from Kentucky in 2 to 4 business days, then 3 to 7 by freight. Shipping is free to all 12 states.