Project Lukewarm

Project Lukewarm was a research programme of the United States Department of Unnecessary Research (DUR) that sought to identify the exact indoor temperature at which no occupant of a shared space would complain. Conducted by the department's Bureau of Thermal Indifference between 1991 and 2019, it was among the longest-running studies in the department's history, involving more than 48,000 participants in 1,377 rooms at a cumulative cost of approximately $31.4 million.

Project Lukewarm

Overview
Agency	United States Department of Unnecessary Research
Component	Bureau of Thermal Indifference
Duration	June 3, 1991 – September 30, 2019
Directors	Ingeborg Salt-Wheeler (1991–2004) Calvin J. Ostermeyer (2004–2019)
Participants	48,212 occupants
Test sites	1,377 rooms in 44 states
Cumulative cost	$31.4 million
Result
Finding	No temperature eliminates complaints
Nearest approximation	70.9 °F (21.6 °C)
Complaint rate at optimum	11.4%

The programme's final report concluded that no such temperature exists. The temperature producing the fewest complaints, 70.9 °F (21.6 °C), still drew objections from 11.4 percent of occupants, roughly evenly divided between those who found it too warm and those who found it too cold. The finding, sometimes called the Lukewarm limit, has been cited in workplace thermostat disputes, in the Office Microwave Accords and in at least two state legislatures.

Background

Complaints about office temperatures had been among the most common categories of constituent correspondence received by the Office of Marginal Inquiry, the DUR's predecessor, which logged 9,400 such letters between 1961 and 1988. Existing engineering standards defined thermal comfort as a range rather than a point, and acknowledged that some proportion of occupants would always be dissatisfied. The founders of Project Lukewarm regarded this as an unexamined assumption. Ingeborg Salt-Wheeler, the programme's first director, wrote in its 1991 charter that "a range is merely a temperature that has not yet made up its mind".

The project satisfied the three statutory tests of the Unnecessary Research Act of 1987 because, according to the department's grant memorandum, "the answer is unlikely to exist, and if found, nobody will set their thermostat to it".

Methodology

Phase I: the Fixed Room studies (1991–1998)

The first phase took place in 64 conference rooms in federal buildings across nine states. Each room was held at a single temperature for a period of two weeks, after which the temperature was adjusted by 0.1 °F. Occupants recorded complaints on standardised Form BTI-7 ("Thermal Objection"), which offered the options "too warm", "too cold", "both, at different times" and "other".

Phase I encountered difficulties with what researchers termed "pre-emptive objection": a tendency of participants to submit complaints before entering the room, based on the temperature they expected. Approximately 14 percent of BTI-7 forms received during the phase were dated earlier than the occupant's first recorded entry. A further 3,100 complaints were attributed to the forms themselves, which were printed on unusually cold paper.

Phase II: Blind thermostat trials (1999–2008)

The second phase introduced placebo thermostats, which could be adjusted by occupants but were not connected to any heating or cooling equipment. Researchers found that 62 percent of occupants who adjusted a placebo thermostat reported feeling more comfortable within ten minutes, regardless of the direction of adjustment. The finding was considered potentially useful and was referred to the department's Inspector General, who ruled in 2004 that it did not constitute "unauthorized necessity" because placebo thermostats were already in widespread use in commercial buildings.

Salt-Wheeler retired in 2004 and was succeeded by Calvin J. Ostermeyer, a former building engineer at the Hollis Annex.

Phase III: Convergence (2009–2019)

The third and largest phase used 1,180 rooms of varying sizes and functions, including offices, waiting rooms, school classrooms, a bowling alley in Lesser Tumbleton, Minnesota and the passenger cabin of a regional bus. Temperatures were controlled to within 0.02 °F by purpose-built units designated "Goldilocks III". Complaints were recorded electronically by means of two buttons, one blue and one red.

Ostermeyer's team applied an iterative narrowing procedure: after each six-month round, the temperature range tested was reduced to the band in which complaints were lowest. The table below shows the results of selected rounds.

Phase III convergence rounds (selected)

Round	Year	Range tested (°F)	Optimum (°F)	Complaint rate at optimum	Too warm : too cold
1	2009	64.0–78.0	71.2	19.8%	47 : 53
4	2011	68.0–74.0	70.6	15.1%	41 : 59
8	2013	69.5–72.5	71.0	13.0%	52 : 48
12	2015	70.4–71.4	70.8	12.2%	49 : 51
17	2017	70.80–71.00	70.92	11.6%	50 : 50
21	2019	70.88–70.94	70.91	11.4%	50 : 50

By round 17 the complaint rate had ceased to fall in any meaningful way, and the ratio of "too warm" to "too cold" complaints had reached parity. Ostermeyer later described this as "the point at which the room begins to argue with itself".

Findings

The final report, published on September 30, 2019, set out four principal conclusions:

1. No indoor temperature produced a complaint rate of zero in any room with more than two occupants.
2. The temperature producing the fewest complaints was 70.91 °F, rounded in the report to 70.9 °F.
3. At this temperature, complaints were evenly split between "too warm" and "too cold", and approximately 2 percent of occupants submitted both.
4. Complaint rates were more closely associated with the identity of the person who last touched the thermostat than with the temperature.

The fourth finding, which the report called the Last Hand Effect, drew considerable attention. Rooms in which a thermostat had been visibly adjusted by a colleague generated complaint rates up to 34 percent higher than identical rooms at the same temperature in which no adjustment had been observed. The report concluded that "the problem is not the temperature; the problem is each other".