Ducks over 8 weeks can tolerate -15 Fahrenheit, so long as they have fresh bedding in a not drafty building. Draft is crucial for you to control.
This'll be the second year I've not supplemented any heat in my coops as I’ve not needed to. I've 4 40x100 uninsulated coops with 1400 ducks in each.
This next bit is lengthy but since I am seeing a common theme of people asking here, I figure this post may be worth writing to provide a method people can assure themselves a bit more than what some guy may say elsewhere.
Technical knowledge:
This is some knowledge from cross disciplines and real-world experience. Your mileage will vary, depending on the factors identified below and whether you use a similar method.
Note: please read about the bird before you raise it. Your responsibility as a farmer is the wellbeing of your birds and the animal’s quality of life. The information provided below is to give you a rough estimation of the available heat your birds emit and what they can utilize.
I am going to structure this to be educational where I explain what you're looking for and how it applies to you. Then I'll run it through my real-world scenario to show you how it performs and to give you a way to understand how to calculate it for your scenario.
Animal heat emissions:
- Ducks emit about 12-14 btu an hour.
- Chicken is 6-10.
- Goose is 14-16.
- Geese need 4 sq ft per bird.
The bigger the bird by weight, the more heat it'll emit. Comparably, all birds will minimally emit 3 btu per sq ft. You can find this by taking the emission btu divided by the needed space requirement. 3 is what I am going to use.
You may think it doesn't matter but relative to the size of your operation, it does. I also always do my calculations based on the most conservative values as it’s better to be prepared for the worse versus only planned for optimal conditions.
My scenario:
I've 1400 Ducks, times 3, equals 4200 btu.
Deep Litter Method (a heat source):
A deep litter bedding system started in June that is at least 6 inches by August will emit 18-24 btu/hr per sq ft. Any additional depth is inconsequential, so long as the method is maintained; additional depth will however aid in sustaining heat for prolong cold snaps (greater than 5 days). So, for the process, assume 18.
My scenario (continued):
I currently have 9 inches of deep litter in place using pine shavings. So, 18 btu times 4,000 sq ft equals 72,000 btu. Now add 5,200. I have 77,200 btu.
Regional effect:
Find your region btu per zone and divide it by 5. 5 is a number used in hvac calculations to quickly determine the base btu requirement to sustain an interior number to a seasonal exterior temperature.
Then take that number times your available interior space. If that number is greater than what your total # animals emit, you may want to consider supplementing heat when temperature falls below -10 F to avoid frostbite.
My scenario (continued):
Where I'm at in WI, 50 btu divided by 5 is 10 btu. Now take 10 times your available sq ft. I've 4,000 sq ft, times 10, equals 40,000 btu as my base heat load requirement. Per the prior step, I am 77,200 btu or 37,200 btu higher or 9.3 btu sq ft above needed. Today, where I'm at, it's 0 F with a constant 20 mph wind from the North, so a lot of wind. Coop interior is 12 F on one of my central thermostats.
In conclusion, my ducks are fine, I know why, and I know how much tolerance they have before I need to help them.
Optional:
Now, if you have the time and money, adding panel insulation to your walls and ceiling will dramatically improve your heat. 2 inch thick 4’ x 8’ rigid foam panels would take your heat up to 20 F in my scenario as it would seal the building better and apply thermal resistance but at a cost of like $15k. However, when you air tighten up a building, mold, especially with ducks which emit a ton of moisture, this will become a new problem if you are not doing enough air exchanges and cleaning effectively. You can use heat exchangers if you really want to keep as much heat in as possible or the more cost-effective way is to use variable fans with carbon dioxide & CFM sensors to sustain a specific CFM in your facility.