The founders of FlexDrill, Sævar Einarsson and Andreas Michalka, asked me for these animations. The background is in Make Europe Cool Again.

This is a hard topic, so animations are much easier to understand than a wall of text.

First, the problem: Vienna is getting hotter.

Vienna · Wien Hohe Warte · 153 years

Vienna’s nights stopped cooling down

One observatory, 153 unbroken years of daily temperature, and where the last thirty years of it point.

Each column is one year at the GeoSphere Austria observatory in the 19th district, counted from the daily values. The dashed line continues the last thirty years to 2050: arithmetic on this record, not a climate model.

DAYS AT OR ABOVE 30 °C PER YEAR · WIEN HOHE WARTE 2024: 45, the highest in the 153 years 0102030405060 about 54 days by 2050 18731900192519501975200020252050 NIGHTS AT OR ABOVE 20 °C PER YEAR · SAME STATION, SAME SCALE 2024: 26, the highest in the 153 years 0102030 about 23 nights by 2050 18731900192519501975200020252050 One column per year, both panels on the same zero baseline and the same scale. The line is fitted to 1996 to 2025, then dashed to 2050. GeoSphere Austria daily data, station 105 Wien Hohe Warte, raw and not homogenised. The dashed line is arithmetic, not a climate projection.

Days at or above 30 °C averaged 6.5 a year from 1873 to 1900 and 31.3 over the last ten. Tropical nights were close to absent for a century: 0.8 a year to 1900, 1.6 in the 1961 to 1990 normal, 11.1 in the last ten. No year before 2015 reached twenty of them, and 2024 reached twenty six alongside 45 days. Summers swing hard, and 2025 fell back to 27 and 7.

Heat kills about three times as many people as the roads

AUSTRIA, JUNE TO SEPTEMBER 2024 989 heat-related deaths Modelled estimate, 95% confidence 607 to 1,355. AUSTRIA, 2024 351 road deaths Counted.

2024 was Austria’s hottest year on record. Heat killed an estimated 989 people between June and September, about 2.8 times the 351 who died on the roads.

Imported natural gas is costly

VIENNA, 2023 0 100% Natural gas, share of grossdomestic energy consumption Fossil carriers, share offinal energy Imported, share of Vienna’senergy 42.6% over 69% 85.8% Financed Russia’s war machine Gazprom supplied Austria until 16 November 2024, and the EU still buys 10 bn euros a year (Commission) Affected by Persian Gulf conflicts The Strait of Hormuz has been shut since 28 February 2026: about a fifth of the world’s LNG stopped moving (EIA) Prone to trade wars In the July 2025 tariff deal the EU said it intends to buy 750 bn dollars of US energy by 2028 (Joint Statement) Vienna’s target: out of fossil heat by 2040. Until then the winter half of the bill is set outside Vienna.
Counted from raw GeoSphere Austria daily data for one station on the leafy northern edge, which is not the whole city. Sources and method

The 153-year series. Days at or above 30 °C and nights at or above 20 °C per year, counted from daily maxima and minima at station 105 Wien Hohe Warte, GeoSphere Austria dataset klima-v2-1d (https://doi.org/10.60669/gs6w-jd70), Creative Commons Attribution 4.0. The day counts reproduce GeoSphere’s own published annual tropical-day totals for every complete year; the night counts are a derivation from the daily minima, not a published GeoSphere product. Every value from 1993 onward was re-checked against the station’s daily record, including 2020, which really did record no tropical night at this station. The daily record is raw, not homogenised: GeoSphere states that homogenised daily Austrian series exist mostly only for the post-war period, so pre-war threshold counts carry instrument and siting uncertainty the modern years do not. The series starts in 1873, the first full year at Hohe Warte; the daily data before that comes from Wien Favoriten and Wien alte Universität, low inner-city sites averaging 16.7 heat days a year, and the step between them is site change, not climate. The dashed line to 2050. An ordinary least squares fit to the thirty years 1996 to 2025, extended to 2050. It gives plus 0.78 days and plus 0.39 nights a year, reaching about 54 days and 23 nights in 2050. This is arithmetic on one station’s record and nothing more: it is not a climate projection, it carries no emissions scenario, and the year-to-year scatter around the fit is about 9 days and 6 nights, which is why the line is drawn dashed and the 2050 values are given as approximate. A fit to the last fifty years instead gives about 46 days and 18 nights, and a fit to the whole 153 years gives about 24 and 8, below where the station already sits, because the record is not a straight line. This station understates the city. Hohe Warte is the leafy 19th district at 198 m. Wien Innere Stadt, the dense core, recorded 52 days and 53 nights in 2024 against 45 and 26 here, but its record only starts in 1985 and cannot carry a long trend, which is why it is not drawn. That nine-year series is published by the Gesundheitsdienst der Stadt Wien (MA 15), Abschlussbericht Wiener Hitze-Gesundheitsmonitoring, Sommer 2025, and the same counting method reproduces it exactly, which is the check that the thresholds match. The annual mean. GeoSphere Austria dataset klima-v2-1y (https://doi.org/10.60669/6yna-mw14), parameter tl_mittel, same station: a decadal mean of 9.92 °C for the 1970s against 12.02 °C for 2016 to 2025, about 2.1 °C. Stadt Wien’s Klimafahrplan monitoring states that since the 1970s the annual mean air temperature in Vienna has increased by close to three degrees Celsius, and records 2023 as the hottest year in nearly two and a half centuries of Vienna measurement. The city does not publish the station or baseline behind its figure, so the two are reported separately and neither is used to confirm the other. The human cost. 989 heat-related deaths in Austria between June and September 2024, 95% confidence interval 607 to 1355, is a modelled estimate from AGES, the national public health agency, Hitze-Mortalitätsmonitoring. 351 road deaths in Austria in 2024 is a count from the Bundesministerium für Inneres, Unfallstatistik. The two bars are drawn to one scale, whose full width is 1,355, for size and not because they are the same kind of number: one is modelled, one is counted. No Vienna-specific heat-death figure or multiple is shown, because the agency’s Vienna estimate for summer 2025 is 48 with a 95% interval of -66 to 153, which includes zero. The energy figures. 42.6 percent gas of gross domestic energy consumption, over 69 percent of final energy fossil and 85.8 percent imported are 2023 figures from Stadt Wien MA 20, Energie in Zahlen 2025; the three shares have different denominators, which is why they are three separate bars. The 2040 exit from fossil heat supply is MA 20’s Raus aus Gas target. No count of Vienna households heating with gas is shown, because no primary source carries one. Financed Russia’s war machine. Gazprom Export supplied Austria on contracts written to 2040, halted deliveries on 16 November 2024, and OMV terminated the contract on 11 December 2024, per OMV’s own release. Austria’s direct Russian supply ended with the Ukraine transit on 1 January 2025: E-Control, the Austrian regulator, calls the country independent of Russian gas from that date, substituting imports from Germany and Italy, while noting in the same report that around 70 percent of what suppliers procured in 2025 has no traceable origin. So the card is written in the past tense on purpose. The 10 billion euros a year is the European Commission’s own figure for what the EU still spends on Russian gas, money it says will “no longer finance Russia nor its aggression against Ukraine” once the phase-out completes; it is EU-wide, not Vienna’s. The Council adopted that stepwise ban on 26 January 2026, with long-term pipeline contracts prohibited from 30 September 2027. Affected by Persian Gulf conflicts. The US Energy Information Administration dates the closure of the Strait of Hormuz to 28 February 2026 and puts the effect at “over 10 billion cubic feet per day (Bcf/d) of global LNG supplies, or approximately 20%”, mostly from Qatar’s Ras Laffan, with no laden LNG vessel crossing between 1 March and 24 April. Iran declared the strait closed on 4 March 2026 and QatarEnergy declared force majeure the same day. The crisis was still running when this page was built, through a cycle of partial reopenings, so the status and any price figure need re-checking before reuse. Prone to trade wars. The United States and the European Union joint statement of 21 August 2025 records that “the European Union intends to procure U.S. liquified natural gas, oil, and nuclear energy products with an expected offtake valued at $750 billion through 2028”, alongside a United States tariff floor of 15 percent on European goods. It is an intention rather than a contract, and roughly three times what the EU spends on gas at current prices, which is why the card says what the EU said it intends and claims nothing about delivered volumes.

Why not just install air conditioning?

Six reasons you cannot cool a Vienna flat with AC

Fitting a real air conditioner, the kind with a unit outside, is often simply not possible in a Vienna building. Five rules stand in the way, and what is left is not much of a machine.

01 Illegal if visible from public space It must not be seen From the street, no. Stadt Wien, MA 19 review of external appearance 02 Noise complaints it runs at night, all summer Your neighbours cannot sleep Many air source units are noisy, and summer nights are when they run. MA 37: air units typically 50 to 75 dB sound power 03 Requires permit § 61 BO, Vienna building code And it is hard to get The permit turns on the same two things: how it looks, how loud it is. MA 37 Leitfaden, its own note on § 61 BO 04 about 14 m, calculated Night sound limit 35dB+6dB at the boundary, plus the corner So you need about fourteen metres you do not have. MA 37 Leitfaden, category 3. 14 m is calculated 05 cool air still on gas No hot water 58% of a Vienna household's energy goes to heat, hot water and cooking It moves air, and nothing else. The radiators stay exactly as they were. Stadt Wien MA 20, Energie in Zahlen 2025 06 Portable AC is poor 2.6kW→1.5kW what it is rated at, and what it puts in the room It holds 2.7 K below outside. A split holds 8 K. Rated EER 2.65, against SEER 5.7 for a split. Heat goes out, warm air comes back in. EU review study of Reg. 206/2012, Tasks 2 and 3

So most people do none of it. In 2024, heat killed 2.8 times as many people in Austria as the roads did: 989 against 351. 989 is a modelled estimate from AGES. 351 is a counted figure from the interior ministry. They are not the same kind of number.

The one system with nothing on the facade and nothing in the courtyard is the one under the building.

The 14 m in panel 4 is calculated from the city's own formula, not a figure Vienna publishes. Sources, panel by panel

Panels 1 and 3. Stadt Wien, "Klimagerät, Begutachtung": a split outdoor unit is permissible where it cannot be seen from public space, and all changes to a building's external appearance are reviewed by the Architecture and Urban Design department, MA 19. The MA 37 Baupolizei guide adds its own warning that a protected zone, a courtyard or a roof position can still make a permit necessary under § 61 of the Vienna Bauordnung, which is why the permit turns on the same two things as the panels either side of it, appearance and noise. Vienna does not ban air conditioning, and none of these panels says it does. Panels 2 and 4. Magistrat der Stadt Wien, MA 37 Baupolizei, "Leitfaden Schallschutz haustechnischer Anlagen". Category 3, dense city housing, carries a night planning value of 45 dB, and the guide requires a 10 dB reduction to reach the base level actually used, which gives 35 dB at the nearest neighbouring boundary. The same guide sets the reflection surcharge at 6 dB in a corner. It states that air-to-water heat pumps run between 50 and 75 dB sound power, which is the basis for panel 2 calling these units noisy. Panel 2 deliberately shows the complaint rather than the limit; the limit is panel 4. The same guide grants a flat 5 dB deduction to units serving heating and hot water and states that the bonus expressly does not apply to cooling and air conditioning, and it does not require the night limit to be proved at all by plant that does not run between 22:00 and 06:00. Neither concession reaches a machine whose whole job is cooling on a summer night. The 14 m is calculated, not published. It follows from the guide's own distance formula, for a 60 dB sound power level picked inside the 50 to 75 dB range the guide gives for these units, in a corner, against the 35 dB night limit. Vienna publishes no such distance. The guide also says of itself that it gives no legal certainty, and that only an expert opinion under ÖAL-Richtlinie 3 Blatt 1 demonstrates compliance. Panel 5. Stadt Wien MA 20, "Energie in Zahlen 2025": space conditioning, hot water and cooking together account for 58 percent of an average Vienna household's energy use. An air conditioner addresses part of the first of those three and none of the other two. The panel claims only that: it moves air, it makes no domestic hot water, and it does not feed the radiators already in the building. No claim is made that such a unit cannot heat air, because a reversible one can. Panel 6. The two capacity figures and the two efficiency figures come from the European Commission's own review of this regulation: Viegand Maagøe and ARMINES, Review of Regulation 206/2012 and 626/2011, Air conditioners and comfort fans, May 2018, for DG ENER. Its base case for a single-duct portable is rated at 2.6 kW, which is also the EU sales-weighted average size, and the study finds it "can only supply 1.5 kW at 2.7 K temperature difference indoor / outdoor", against the 8 K a properly sized fixed split holds at 35 °C outdoor. Those two kW figures are one simulated base case at one operating point, not a measured ratio for the category: US DOE states that differing air flows and heat losses "would preclude a fixed translation factor", so no percentage is claimed here. Rated EER 2.65 against SEER 5.7 are the study's sales-weighted declared values across ten EU countries, and they remain two different measurements, which is the point. The regulation's own floors, for reference, are SEER 4.6 for a split under 6 kW against a rated EER of 2.6 for a duct unit. The mechanism drawn, air blown out of the window being replaced by outside air pulled in through every gap, is the reason the category is regulated separately. Double-duct units behave better and are rare in the EU. The line below the strip. AGES heat mortality monitoring for the 989 heat-related deaths estimated in Austria from June to September 2024, which is a modelled attribution of excess mortality and not a count. Bundesministerium für Inneres for the 351 road deaths counted in Austria in 2024. The comparison is Austria-wide on purpose: the AGES estimate for Vienna alone has an interval that includes zero. What the strip does not argue. Not that air-source heat pumps fail. Only the narrower thing the panels show: the leniencies in this method, the 5 dB bonus and the exemption for plant that does not run at night, are written around heating-season and daytime running. Cooling meets neither.

Ground-source heat pumps solve this, but a conventional drilling rig cannot get into a Vienna courtyard.

The attempt: a rig that reaches 200 m tries to get into a Vienna courtyard garden

Two hard stops at the way in, what the machine does to the only open ground the block has, and the trench and the indoor work that still follow the hole. A generic Gründerzeit street, drawn to one scale above ground.

cut through the front wing 0 m2050 100150200 m depth below ground depth compressed below 20 m borehole width exaggerated to stay visible 2.5 m to the neighbouring plot 3.20 m passage height most rigs need (VÖBU) 7.5 t 7.5 t, drills to 200 m minimum access width 1.5 m 2.3 m clear height of this gate 1.4 m access width Beretta T41, distributor listing the mast jams under the 2.3 m soffit 2.3 m transport height 4.95 m operating height, same machine about 1.5 t of spoil per 100 m drilled. 200 m of hole: about 3 t. basement, drawn schematically trench back across the garden and connected up inside churned ground, standing water The same gate, seen head on 3.20 m x 2.50 m VÖBU: enough for most rigs. That is the dashed rectangle. 2.3 m x 0.85 m Stadt Wien: drilling is still technically possible at this, but only at shallower depths. 1.5 m minimum access width of the rig standing on the street.
Down the street
Sources and drawing notes

Access clearances. Stadt Wien, “100 Projekte Raus aus Gas”, FAQs Tiefenbohrungen im öffentlichen Raum (version 25.02.2025, produced with MA 28 and MA 45): drilling is still technically possible at a passage height of 2.3 m and a width of 0.85 m, though often only at shallower depths, while the Austrian drilling association VÖBU gives 2.50 m width and 3.20 m height as sufficient for most rigs. The same FAQ carries the 2.5 m minimum distance to the neighbouring plot, which comes from ÖWAV-Regelblatt 207. Machines. Beretta T41: 1.4 m access width, 2.3 m access height with the mast down, 4.95 m operating height, from a distributor listing seen only as a search snippet, so treat it as indicative. Comacchio GEO 205: 2.4 to 2.8 t, mast 2.6 to 4.7 m, boreholes in excess of 50 m, manufacturer datasheet. The 7.5 t tracked rig at 1.5 m minimum access drilling to 200 m, and the 2.8 t machine reaching about 100 m with “limited power reserves”, both come from one German contractor’s public equipment list (Hartmann GmbH) describing its own fleet. That is one company, not a survey of the market, and neither pair is an industry standard. Nothing on screen should be read as a market-wide access figure: the only clearances with a norm behind them here are the VÖBU and Stadt Wien ones above. Depths, output and spoil. Austrian closed loops average 107 m plus or minus 36, GeoBOOST deliverable D2.1. Roughly 3 to 5 kW from a 100 m borehole, and about 1.5 t of spoil per 100 m drilled, are trade figures. The “about 3 t” on screen is arithmetic on that trade figure, 200 m at about 1.5 t per 100 m, and it assumes the same hole diameter throughout. No source here gives a volume of flushing water, a number of working days, an area of ground disturbed, a length of connecting trench or a cost of putting a garden back, so none of those is stated. The last beat shows the trench from the borehole to the building and the connection inside it because both are part of the same job, and puts no figure on either. Drawing. Everything above ground is one scale, 28 pixels per metre. Machine heights are drawn at the sourced figures and the access widths are named where they are quoted; the horizontal extent of a machine in this side view is its length, which no source here gives, so lengths are illustrative. Below ground is a different, smaller scale, marked by the depth scale beside the boreholes: the first 20 m at one rate and everything below it compressed again, with the break drawn across the soil and labelled. Borehole width is exaggerated to stay visible, and the trench and the basement in the last beat are drawn at a legible size rather than at either scale. The block, the houses along the street and the garden are all generic: the houses are drawn apart so the street reads as separate buildings, and no frontage, gap between houses, passage width, courtyard size, storey height or planting here is attributed to a real address. The ruts, spoil, puddles, hoses, trench and basement plant are an illustration of the kind of working site a rig makes, not a survey of one. The hole count and spacing in the last beats are illustrative, not calculated for any building. Transport height and operating height are kept apart throughout, in both directions. What this does not claim. Not that drilling from a courtyard or a basement is impossible. Boreholes have been drilled from inside an occupied building and a patent for low headroom geoexchange drilling has been granted. The defensible statement is availability, not possibility: in this research, nothing commercially available was found that reaches 100 m or more in very low operating headroom. Compact rigs are not claimed to be incapable of depth; what is sourced is that the specific machines found trade depth for size. No setback from an existing building is asserted, because no regulator was found stating one. No FlexDrill figure appears anywhere in this piece.

What FlexDrill is designed to do instead: one borehole, one day, from a basement.

One borehole, one day, from a Vienna basement

A terraced house with no courtyard. The trailer never leaves the kerb.

0 m1020 50100150 200 m scale breaks here 0 m Vienna’s ground: 14.1 °C year round, and about 3 °C warmer every 100 m further down 1 m heat pump FLEXDRILL
Trailer at the kerb
Pre-commercial: every FlexDrill figure here is a company target. Sources and disclosure

Disclosure. The author is an angel investor in FlexDrill. The company is pre-commercial and has not drilled a full-depth borehole, so every FlexDrill number here (200 m, 1 m² footprint, one working day for the borehole, kit out the next morning, cuttings filtered in the trailer) is a company target, not a measured result. Sources. System description and schedule: flexdrill.at technology page and FAQ, which give 8 to 10 hours of drilling, 1 to 2 further days for the heat pump and indoor work, and 2 to 3 working days of total disruption. Full-length bottom-up grouting, gap-free and freeze-thaw stable: Stadt Wien MA 45, Merkblatt Tiefsonden, standard condition 4. Drill spoil and drilling water must be contained on site and must not reach the sewer, a watercourse or a neighbour's land: Amt der Tiroler Landesregierung, Leitfaden Erdwärmesonden, §7.1.3. Ground temperature: Vienna's shallow subsurface averaged 14.1 °C in 2021/22, measured city-wide in the 'Heat below the City' project (Kaminsky et al., EGU General Assembly 2024, abstract EGU24-9552); across 812 locations the range was 6.9 to 30.6 °C, so a site needs its own measurement, and the figure is rising by about 1 K per decade. Temperature climbs roughly 3 °C per 100 m of depth. Drawing. Depth is compressed below 20 m and the borehole width is exaggerated; a real borehole is about 15 cm across. Everything above ground, trailer and trolley included, is one scale.

It is cool what you can do with Claude Code and Fable over the weekend. I hope they will use these in their materials. I feel screenshotting is a game changer in Opus 5 and Fable.