Quick answer
Denver's average first freeze is October 7 and its average last freeze is May 5, per the National Weather Service. To prevent frozen pipes, disconnect hoses and drain sprinkler lines in fall, insulate pipes in exterior walls and unheated spaces, and drip the farthest faucet in deep cold. When away, the Red Cross says keep heat at 55 degrees or more; Denver Water says above 65.
Updated · By the Denver Plumber Pros editorial team · How we research
How long is Denver's freeze season?
Longer than many people expect. The National Weather Service office in Boulder lists Denver's average first fall freeze as October 7 and average last spring freeze as May 5. January is the coldest stretch: the 1991 to 2020 normals put average lows around 18 to 19 degrees Fahrenheit, and Denver's record low is minus 29 degrees, set on January 9, 1875 (NWS January climate record). Front Range cities also design foundations for frost: Arvada, Aurora and Thornton list a 36 inch frost depth in their building criteria.
Which pipes freeze first?
The American Red Cross lists the pipes most at risk:
- Outdoor hose bibs, swimming pool supply lines and sprinkler lines
- Supply lines in unheated spaces such as basements, crawlspaces, attics and garages
- Pipes that run along exterior walls with little or no insulation
In Denver-area homes, that usually means the hose bib on the north side of the house, the line feeding a sprinkler backflow device, kitchen sink lines on an outside wall and pipes in an attached garage.
Fall checklist: before the first freeze
- Find your main shutoff. Denver Water's frozen pipe tips say to learn where your home's water shutoff valve is and make sure everyone in the household can operate it.
- Disconnect hoses. The Red Cross says to disconnect and store outdoor hoses, close the indoor valves that feed outdoor spigots, and leave the outdoor spigots open so trapped water can drain.
- Drain irrigation. Drain sprinkler and pool supply lines following the manufacturer's or installer's directions, and do not use antifreeze unless told to.
- Insulate. Insulate pipes along exterior walls and in unheated basements, attics and crawlspaces. Pipe sleeves or UL-listed heat tape help.
- Seal the garage. If water lines run through an attached garage, keep the garage door closed.
What should you do during a cold snap?
- Open sink cabinet doors on outside walls so indoor air reaches the pipes.
- Denver Water suggests cracking the faucet farthest from where water enters the house to a very slow drip; catch the water in a bucket for other uses.
- The Red Cross advises keeping the thermostat at the same temperature day and night.
What temperature should you leave the heat at when you travel?
The two sources differ. The Red Cross says to keep the heat on at no lower than 55 degrees Fahrenheit if you will be away in cold weather. Denver Water recommends a thermostat setting above 65 degrees when you leave your house or business for several days. For a long trip in January, the higher setting is the safer choice, and shutting off and draining the water supply is another option to discuss with a plumber.
How do you thaw a frozen pipe safely?
| Do | Do not |
|---|---|
| Shut off the water or test the shutoff valve first | Use a blowtorch or any open flame |
| Open the faucet so melting water can flow out | Use a kerosene or propane heater or charcoal stove |
| Warm the pipe slowly with a hair dryer, heating pad or hot towels | Leave a space heater near anything flammable |
| Check other faucets, since one frozen pipe often means others | Wait if you cannot find or reach the frozen section |
A weak trickle from a faucet is a common sign of a frozen pipe, and frozen spots are often near exterior walls or where the water line enters through the foundation, per the Red Cross. Denver Water says slower thawing is better. If you cannot locate the frozen section, or the pipe has already split, call a licensed plumber.
If a pipe bursts
Shut off the main valve immediately, then turn off power to any wet electrical circuits if it is safe to do so. Our emergency plumber guide covers the next steps, and emergency plumbing services explains what a repair visit involves. Typical burst pipe repair costs are in our Denver cost guide. Homes with boilers have extra freeze risk if the heat goes out; see boiler maintenance.
About this guide
We are an independent homeowner guide, not a contractor, and we are not an emergency service. If a pipe has burst and you want help finding a licensed local contractor afterward, you can email us a request.
Frequently asked questions
At what temperature do pipes freeze in Denver?
Water freezes at 32 degrees Fahrenheit, but whether a pipe freezes depends on how exposed it is, how long the cold lasts and whether water is moving. Denver's average January lows are around 18 to 19 degrees, so exposed hose bibs, garage lines and pipes on uninsulated exterior walls are at risk every winter.
Should I let faucets drip in Denver when it is very cold?
Yes, for faucets fed by exposed pipes. Denver Water suggests cracking the faucet farthest from where water enters the house to a very slow drip, and catching the water in a bucket. Moving water is less likely to freeze, and an open faucet relieves pressure if ice forms.
When should I blow out my sprinkler system in the Denver area?
Plan to drain or blow out irrigation lines before Denver's average first freeze on October 7, per National Weather Service records. The Red Cross advises following the manufacturer's or installer's directions and not using antifreeze unless directed. Close the backflow valves as instructed for your system.
Sources
Independent homeowner guide operated by SWKM GmbH. Not a licensed contractor. We do not perform plumbing work. More about this site.