The furnace has not run since spring. The wood stove gets lit, the generator comes out for the first storm, and the truck warms up in the garage. Every one of those is a carbon monoxide source, and pets usually show it first. A working detector and a few habits handle almost all of it.
Why pets show it first
Carbon monoxide has no smell, no color and no taste. It binds to red blood cells far more readily than oxygen does, so the blood stops carrying what the body needs while everything appears normal.
Pets reach that point sooner than we do. They are smaller, they breathe faster relative to their size, and they spend the whole day in the house rather than leaving for work or school. Birds are the extreme case and the reason miners carried canaries, but dogs and cats are also affected well before the adults in the household notice anything.
That is the useful part for owners: a pet who is repeatedly unwell at home and improves when they leave is telling you something about the building.
Where it comes from in a Skagit Valley fall
- A furnace that has not run since March, with a cracked heat exchanger, a blocked flue or a bird’s nest in the vent
- Wood stoves and fireplaces with a poor draw or a dirty chimney
- Gas appliances: water heaters, ranges, dryers and space heaters
- Generators run during a power outage, which is the classic and most dangerous one
- Vehicles and equipment idling in an attached garage, even with the door partly open
- Blocked exhaust vents, including ones buried by leaves or snow at ground level
- Propane heaters used in a shop, barn or enclosed porch where animals are kept
What it looks like in a dog or cat
The signs are vague, which is exactly the problem. Early on you may see:
- Sleepiness, dullness, or a pet who seems off with no other explanation
- Vomiting, or refusing food
- Unsteadiness, weakness, or stumbling
- Rapid breathing
- Bright red gums, though this is not reliable and its absence proves nothing
- Later: collapse, seizures, or an animal who cannot be roused
The pattern that should make you suspicious is more useful than any single sign. Several animals in the house unwell at once. A pet who is worse in the morning and better by evening. Everyone in the household, including the people, with headaches and nausea that ease outdoors. A pet who perks up on a walk and dulls again indoors.
If you suspect it
- Get everyone out, including the animals, into fresh air immediately.
- Do not stop to open windows or find the source. Leave first.
- Call 911 or the fire department from outside.
- Do not go back in until it has been cleared.
- Bring your pets to us, and say you suspect carbon monoxide. Our urgent care team handles that history differently from an ordinary case of lethargy. We are closed on weekends, and outages rarely wait for a Tuesday, so if this happens when we are shut, go straight to the nearest open emergency hospital.
Blood testing through our medical services and oxygen support are the practical first steps, and pets exposed to a significant amount are monitored rather than sent straight home, because some effects appear later.
Prevention, which is mostly one purchase and two habits
- Install carbon monoxide detectors on every level and near sleeping areas, Press the test button once a month, change the batteries when you change the clocks, and replace the units themselves every few years, since the sensors expire.
- Have the furnace, water heater and chimney serviced before the season, not after something goes wrong.
- Never run a generator indoors, in any garage, attached or not, or in a partly enclosed space. Put it at least twenty feet from the building, with the exhaust pointed away from doors, windows and vents.
- Never warm a vehicle in an attached garage, even with the door up.
- Do not use a barbecue, camp stove or propane heater indoors, including in a barn or shop where animals live.
- Keep exterior vents clear of leaves, nests and snow.
- If you keep birds, take the alarm even more seriously. A bird who becomes unwell suddenly is worth acting on.
The wider heating-season picture
The same weeks bring space heaters within reach of pets who want warmth, new cords across floors, and fireplaces with glass doors that stay hot long after the fire dies. Keep a clear space around every heat source, use a fireguard, and give older pets a warm bed away from the appliance so they are not pressed against it. An older pet who presses against the heat all day may be stiff, which is worth a wellness program visit to look into.
Fall brings a different set of outdoor risks at the same time, which our guide to hunting season safety for dogs covers.
Frequently asked questions
Will my smoke alarm detect carbon monoxide?
No, unless it is specifically a combination unit. Smoke alarms and carbon monoxide detectors sense completely different things, so check what you actually have on the ceiling rather than assuming.
My dog was sleepy all day but seems fine now. Should I still call?
Call if anything about the house fits the pattern, such as other animals affected, people with headaches, or the furnace or a generator having run. It costs a phone call, and the alternative is a repeat exposure the next cold evening.
Are cats or dogs more sensitive?
Both tend to show it sooner than the adults in the house, and smaller animals sooner again. Birds are the most sensitive of all. Practically, regard any species in the house as an early warning rather than trying to rank them, and do not read the other way round: a pet who seems fine is not evidence that the air is safe. Infants, older adults, pregnant people and anyone with a heart or lung condition are more vulnerable too.
We run a generator during outages. What is the safe distance?
At least twenty feet from the building, never in a garage or under a carport, with the exhaust directed away from doors, windows and vents. Outages are exactly when these poisonings happen, because people put the generator somewhere sheltered from the rain.
Is it safe for my dog to sleep by the heating vent?
Generally yes, provided the system is serviced and detectors are working. What is worth noticing is a change: a dog who suddenly wants to be there all the time, or who is dull whenever the heat is running, is worth mentioning.
How long do detectors last?
The sensors have a limited life, typically several years, and the unit should have a replacement date printed on it. A detector that is a decade old may look fine and do nothing at all.
Speak to the team at Sedro-Woolley Veterinary Clinic
If your pet has been dull or unsteady at home and you suspect the air, get everyone outside, call for help, and then call us.
Published by the team at Sedro-Woolley Veterinary Clinic.
This article is for general educational purposes only and is not a substitute for an in-person veterinary examination or advice about your individual pet. If you have an urgent concern about your pet, contact Sedro-Woolley Veterinary Clinic or your nearest emergency veterinary hospital right away.
Sedro-Woolley Veterinary Clinic
207 Carter Street, Sedro-Woolley, WA 98284
Phone: (360) 856-6890
Hours: Monday to Thursday 7:30 am to 6:00 pm; Friday 8:00 am to 6:00 pm; Saturday and Sunday closed