We were recently adopted by a dog. In the middle of a minor wind storm, she appeared on our front porch, thin to the bone. We immediately did what we could, and with temperatures in the upper 80s during the day and 70’s at night, we set her up with a temporary shelter.
Our house already has three indoor pets, two cats and an African Grey parrot. We did not know how well she would handle being inside, so we kept her outside while we searched for her owners. We never found them, so after a few weeks it was time to build or buy a more permanent shelter.
We bought a quick-and-cheaply-made wooden dog house from Petsmart, which so long as the nights were still warm was perfectly fine. However, as the nights became colder, and we were predicted to have a few days below freezing, it was time to make sure she could stay warm in her outdoor life.
I went to Home Depot and picked up some 3/4” finished-one-side plywood, some 1/4” finished-one-side plywood, some 3/4” foam insulation, and some construction adhesive.
First was to make the floor as stable as possible. I covered it with the foam insulation, and then with the 3/4” plywood. Considering the dog house was so flimsy before, this is a major stability upgrade. The rest of the walls and ceiling were covered with insulation, and then in 1/4” plywood.
For the door, my lovely wife made a door cover out of some spare canvas we had, about three layers thick. We weighted it down in the corners with some large washers, to keep it from flapping too much in the wind.
The observed change in temperature was around 12 degrees F when she was inside the house, and it took about an hour to reach that maximum. This seemed pretty consistent down to a starting temperature of 40 F, where she would raise the inside air temperature to 52 F. When it was colder, say 32 F, it rose to about 44 F. If it was windy, it took much longer, and usually only rose about 8 to 10 F.
We were predicted to have several days (and nights) in a row where it was going to be around 24 F, and I do not think her body heat alone would keep up. I opted to add a heat source, but none of the just-buy-it heat sources were ones I thought would work well.
Her house has a thick foam bed and many blankets, which she rearranges on a regular basis. She currently has a small nest, which works well, and keeps her away from the walls, which while insulated are always cooler than the inside air.
I selected a 60 watt ceramic heating element from Petsmart, intended to be used as a terrarium heater. I selected 60 watt from the several options mostly because I thought it would more than suffice, and while I could have selected the 100 watt unit, it would increase the chance of a fire should she cover the element up entirely.
The wire shield around the element is a double-layer of wire mesh, attached to the ceramic base using cable ties. The top, which had some sharp edges, was wrapped in a few layers of duct tape. I drilled two holes to attach the ceramic bulb holder to the house, and a hole exactly large enough to feed the 120 VAC power feed through the wall.
There are no exposed wires for her to chew inside the dog house, and the metal cover keeps her and her bedding away from the heating element. The whole thing is mounted low in the house since convection is the only air movement available.
I did add a standard incandescent light dimmer from Home Depot, so I could select the energy output from 0 W to the full 60 W. I do not yet have the monitoring system (described below) able to turn the unit on and off to maintain a steady temperature, so this crude system is all I have.
The dimmer is mounted in a 2-gang outdoor box, with weatherproof cover, along with a standard 2-plug outlet to let me power small devices like the monitoring system.
I set the power output to around 40 watts, which maintains a 18 F rise from the outside air temperature. With her inside, it rises another 10 F or so, bringing the inside temperature to between 52 F and 60 F.
There are three sensors inside the house, and one outside. The dark green is the outside, and the purple, orange, and light green are sensors at various places inside the dog house, attached to the plywood.
the “bump” in the graph between 13:30 and 15:45 is where she was inside the house, sleeping. The little bump around 14:45 is where she must have left to take care of some business. The very small blip on the right hand side is where I opened the canvas door flap to check the inside for warmth and safety.
Being the geeky type I am, I hooked up some temperature monitoring. Chances are most people won’t need to do this, but I wanted to find out just how much her body heat was able to warm her home up, amid her piles of blankets and fairly well insulated house.
In the upper left is a pill bottle, lid attached to the house, holding the monitoring gear.
- A Arduino Pro Mini 328 - 3.3V/8MHz Arduino from Sparkfun Electronics.
- A Xbee 2.4 GHz S2B model Zigbee radio from Digi International (http://www.digi.com/)
- A Breakout Board for XBee Module to make it easy to use the XBee modules without soldering directly, also from Sparkfun Electronics. Don’t forget the 2mm 10-pin headers!
- Four Dallas DS18B20-PAR One-Wire Digital Thermometer.
- A small power supply that takes the 5 VDC from the wall-wart adapter and converts it into a regulated 3.3 VDC. While the Arduino board has a 3.3 VDC regulator, it cannot supply the current necessary for transmission on the Xbee.
The receiver is a small, low-power-consumption computer that reads the temperature data, and creates graphs. I’ll dedicate a blog posting to this component alone at some point.