Why passive solar fits Wichita
Three local facts make the case.
Winter sun. Wichita receives sunshine about 58% of possible daylight hours in January, based on NCDC comparative climatic data. That matches Kansas City and trails western Kansas (Dodge City 67%). January is when a solar greenhouse earns its keep.
Winter sun angle. At 37.69°N, the noon sun on December 21 stands 28.87° high (90 − 37.69 − 23.44). That's 1.4° higher than Kansas City. Low sun comes in under the roofline and reaches deep into the house, so the back of the greenhouse gets light, too.
Zone 7a. The 2023 USDA map moved Wichita from zone 6b to 7a. Typical first fall freeze falls between Oct 20 and Nov 4, and the last spring freeze between Apr 5 and 14, per NWS Wichita. A passive solar house stretches both ends of that window.
The cost of winter is real, though. Wichita averages 4,592 heating degree days a year, with 986 in January and 911 in December (1991–2020 normals). Passive solar is how you cut the share of that load you pay for in gas or electricity. Our one-winter heating guide runs the numbers.
The five design decisions
| Decision | What we do in Wichita | Why |
|---|---|---|
| Orientation | Long axis east-west, glazing faces true south | Maximizes glazing area facing the low winter arc |
| North wall | Opaque and insulated, light-colored inside | Little winter sun comes from the north; this wall loses heat and gains almost nothing |
| Glazing tilt | 48°–61° from horizontal, chosen by season | Perpendicular to Dec noon sun is 61.1°; latitude + 10–15° is 48–53° |
| Thermal mass | Water barrels, masonry or earth | Stores daytime heat for the night |
| Venting | Large, high and low vents; automated openers | Kansas summers overheat glazed buildings fast |
Orientation: east-west long axis
A greenhouse with its long side facing south presents the most glazing to the winter sun. We site the ridge east-west and aim the glazing at true south, not magnetic south. Shade from trees, fences and your house matters more in winter than in summer, because winter shadows are long. At the December solstice, any obstacle shades about 1.81 times its height at noon.
Insulated north wall
In winter, the sun sits in the southern sky. A glazed north wall loses heat all night and gains little by day. We build the north wall (and often the east and west ends) as framed, insulated walls. The inside face gets a light or reflective finish to bounce light back onto your benches.
Glazing tilt
There are two ways to set the angle.
- Perpendicular to the December noon sun: 90 − 28.87 = 61.1° from horizontal. Best for midwinter gain.
- Rule of thumb, latitude + 10–15°: 48–53°. A compromise that performs better in February, March and October.
If your goal is greens through January, we lean steep. If it's spring seed starting, we lean shallower. The sun-angle guide shows how the incidence angle changes by month. Glazing material is a separate choice; see polycarbonate vs. glass and our hail-resistant glazing guide. We'll tell you which panel lines fit your budget and hail exposure when we quote.
Thermal mass: a worked example with water barrels
Water stores a lot of heat for its volume. One cubic foot weighs about 62.4 lb and takes about 1 BTU per pound to warm 1°F, so it holds about 62.4 BTU per °F.
Take ten 55-gallon drums along the north wall:
- Volume: 10 × 55 = 550 gallons ÷ 7.48 gal/ft³ = 73.5 ft³
- Storage: 73.5 × 62.4 = 4,588 BTU per °F
- If the water warms 10°F during a sunny day and gives it back overnight: 4,588 × 10 = 45,880 BTU
- At a 20°F swing: 91,760 BTU
Now the night loss. These inputs are assumptions for illustration; replace them with your design's numbers: 200 ft² of south glazing at U = 0.6 BTU/hr·ft²·°F, 300 ft² of insulated walls at U = 0.05, inside held at 40°F with 10°F outside (a 30°F difference), for a 14-hour January night.
- Glazing: 200 × 0.6 × 30 × 14 = 50,400 BTU
- Walls: 300 × 0.05 × 30 × 14 = 6,300 BTU
- Total: 56,700 BTU
On these assumptions, a 10°F swing in ten drums covers about 80% of that night's loss (45,880 ÷ 56,700). The glazing is 89% of the loss, which is why night insulation matters so much. Weight matters too: 550 gallons of water is about 4,590 lb, so we plan the floor and footings for it. See greenhouse foundations.
Two cautions. Water only gives back heat when it's warmer than the air, so a cloudy stretch drains the bank. And this is one night, not a season; a run of gray January days still needs backup heat.
Night insulation
Because the glazing loses most of the heat, covering it at night pays off. Options include interior thermal curtains on tracks, insulated panels that fit the glazing bays, and bubble insulation on the inside face. In the example above, cutting the glazing loss in half would cut the total night loss by about 44%.
Venting for Kansas summers
A passive solar greenhouse is built to collect heat, and in a Kansas summer that becomes a problem fast. We design for:
- Low intake and high exhaust vents so hot air rises and leaves by itself.
- Automatic vent openers so the house doesn't cook while you're at work.
- Shade cloth for the south face in midsummer.
- An exhaust fan option for hot, still days.
The same steep glazing that catches December sun sheds some of the high June sun. At the June solstice, Wichita's noon sun is 75.8° high, so it strikes 61° glazing about 47° off perpendicular (75.8 − 28.9), compared with 0° in December. More of it reflects away.
Wind and structure
A passive solar house has a tall, solid north wall that acts like a sail. Our framing and anchoring follow Wichita design wind loads; see the wind-rated greenhouse design guide.
Passive solar vs. earth-sheltered vs. climate battery
Passive solar is the base layer. You can add an earth-sheltered design that sets the floor 3–4 ft below grade, or underground air storage. Each adds cost and adds heat. We'll tell you which one your goals justify.
Pricing depends on size, glazing, mass and site work. National cost guides rank solar greenhouses as the most expensive style, at about $35–$45 per sq ft (LawnStarter, Dec 2025). Insulated-panel kits run higher: Ceres lists its 18 × 24 ft BackYard kit at $68,277, before shipping and installation (Ceres, Oct 2026). Timing depends on season, permits and materials; your quote gives a schedule.
Frequently asked questions
Does a passive solar greenhouse work in Kansas winters?
Yes, with backup heat for cold, cloudy stretches. Wichita gets about 58% of possible January sunshine and a 28.87° noon sun at the December solstice. A well-oriented house with insulated north wall, steep glazing and thermal mass captures a large share of its own heat.
What angle should passive solar greenhouse glazing be in Wichita?
61.1° from horizontal is perpendicular to the December 21 noon sun. The common rule of thumb, latitude + 10–15°, gives 48–53°, which works better for spring and fall.
How many water barrels do I need?
It depends on glazing area and night temperatures. In our worked example, ten 55-gallon drums store 4,588 BTU per °F. A 10°F daily swing covers about 80% of an assumed 56,700 BTU January night loss for a house with 200 ft² of glazing.
What USDA zone is Wichita?
Zone 7a on the 2023 USDA map. It was zone 6b on the previous map.
How do I keep a passive solar greenhouse from overheating in summer?
Use low intake and high exhaust vents with automatic openers, shade cloth on the south face, and an exhaust fan for still days. Plan venting at design time, not after the first hot week.
Get a quote
Tell us where it will sit and what you want to grow. We'll set the orientation, glazing angle and thermal mass to fit your goals and your lot.