In 2020, we earned more than 20% of our revenue in Texas, where we have multiple strong mechanical capabilities in many markets, and Texas is also the home to our largest electrical team.
We finished the year with strong fourth quarter earnings per share of $1.17, and for the full year, we earned $4.09.
Revenue for full year 2020 was also a record at $2.9 billion.
Our 2020 free cash flow was an unprecedented $265 million.
At the end of 2020, we acquired a Tennessee Electric Company headquartered in Kingsport, Tennessee, and we expect they will contribute $90 million to $100 million of revenues in 2021.
Trent has been with Comfort Systems USA for 16 years, and I believe he will be a valuable leader, as we continue to grow and improve our operations.
So fourth quarter revenue was $699 million, a decrease of $21 million compared to the same quarter last year.
Our same-store revenue declined by a larger $68 million.
However, our recent acquisitions of TAS and Starr offset that decline somewhat as they added $48 million in revenue this quarter.
Revenue for the full year was $2.9 billion, an increase of $241 million or 9% compared to 2019.
Full year same-store revenue in 2020 was 2% lower than in 2019 due to the factors I just mentioned.
Gross profit was $137 million for the fourth quarter of 2020, an increase of $4 million.
And gross profit as a percentage of revenue rose to 19.6% in the fourth quarter of 2020 compared to 18.4% for the fourth quarter of 2019.
For the full year, gross profit increased $45 million, and our gross profit margin was approximately flat at 19.1%.
SG&A expense was $89 million or 12.7% of revenue for the fourth quarter of 2020 compared to $87 million or 12% of revenue for the fourth quarter of 2019.
The prior year fourth quarter benefited from insurance proceeds associated with the cyber incident of approximately $1.6 million, and that reduced SG&A last year.
For the full year, SG&A as a percentage of revenue was 12.5% for 2020 compared to 13% for 2019.
On a same-store basis, for the full year, SG&A declined $6 million, and that decrease was primarily due to austerity relating to COVID, such as reductions in travel-related expenses.
During the fourth quarter of 2020, we revalued estimates relating to our earn-out liabilities, and as a result, we reported an overall gain of $7 million or $0.18 per share.
For the full year, the gain associated with acquisition earn-out valuation changes was $0.20 per share.
Our 2020 tax rate was 21.6% compared to 24.7% in 2019.
On a go-forward basis, we now expect our normalized effective tax rate will be between 25% and 30%.
Specifically, net income for the fourth quarter of 2020 was $43 million or $1.17 per share as compared to $34 million or $0.92 per share in 2019.
Earnings per share for the current quarter included that $0.18 gain associated with earn-out revaluations.
Our full year earnings per share was $4.09 per share compared to $3.08 per share in the prior year.
The current year also included a tax benefit of $0.17 that we reported in the third quarter of 2020 from a discrete tax item.
The gains associated with earn-out revaluations, which for the full year was $0.20.
For the fourth quarter, EBITDA was $63 million, which is 6% higher than the fourth quarter of last year.
Our annual 2020 EBITDA was a milestone achievement for us, as our full year EBITDA was $250 million.
Our full year free cash flow was $255 million compared to $112 million in 2019.
Our 2020 cash flow includes roughly $32 million of benefit, that's a direct result of the Federal Stimulus Bill, which allowed us to defer payroll tax payments in the last nine months of 2020.
2020 was our largest year for share repurchases in quite some time, as we reduced our overall shares outstanding by repurchasing 685,000 of our shares at an average price of $43.99.
Since we began our repurchase program in 2007, we have bought back over 9.3 million shares at an average price under $20.
Our backlog level at the end of the fourth quarter of 2020 was $1.51 billion.
Sequentially, our same-store backlog increased by $10 million, with particular strength in our modular backlog.
Same-store backlog compared to one year ago has decreased by $375 million, of which approximately, 1/3 related to an expected decline in our electrical segment.
Our industrial revenue has grown to 39% of total revenue in 2020 compared to 34% a year ago.
Institutional markets, which includes education, healthcare and government, were 36% of our revenue, and that is roughly consistent with what we saw in 2019.
The commercial sector was 25% of our revenue.
For 2020, construction was 79% of our revenue with 47% from construction projects for new buildings and 32% from construction projects in existing buildings.
Service was 21% of our 2020 revenue with service projects providing 8% of revenue and pure service, including hourly work, providing 13% of revenue.

Summary:
We finished the year with strong fourth quarter earnings per share of $1.17, and for the full year, we earned $4.09.
So fourth quarter revenue was $699 million, a decrease of $21 million compared to the same quarter last year.
Specifically, net income for the fourth quarter of 2020 was $43 million or $1.17 per share as compared to $34 million or $0.92 per share in 2019.
Our backlog level at the end of the fourth quarter of 2020 was $1.51 billion.