One of the fires, on Saturday, involved a tent pitched that had been in a wooded area in Bel Air's west side commercial district.
The first fire occurred Friday, when firefighters were dispatched to a home in the 700 block of Shirley Drive in Aberdeen at about 5 p.m.
The one-alarm blaze was caused by an "unknown malfunction" with the natural gas boiler in the basement of the one-story, wood-framed home, according to the Fire Marshal's Office's notice of investigation.
The fire caused $20,000 worth of damage to the structure and $10,000 to its contents, according to the Fire Marshal's Office. A smoke alarm did not activate and the home did not have sprinklers.
It took 25 firefighters from Aberdeen, Level and Aberdeen Proving Ground fire companies about an hour to control the fire.
On Saturday, a fire was reported in a garage or shed the 500 block of Magnolia Road in Joppa at about 12:11 p.m.
A detached garage caught fire from a propane torch that had been lit close to combustibles, according to the Fire Marshal's Office's notice of investigation.
The fire caused $10,000 worth of damage to the garage and $5,000 to its contents. There was no smoke alarm in the garage.
About 25 firefighters from Joppa, Aberdeen Proving Ground, Abingdon and Bel Air responded to the incident and controlled it within 30 minutes.
According to monitored Harford County emergency radio broadcasts, the fire was originally reported in the 500 block of Mountain Road in Fallston, which caused some confusion among responding units. Both addresses are along Route 152 but are several miles apart, because the highway changes names from Mountain Road to Magnolia Road south of Route 40.
Four hours later, a camping tent caught fire in a wooded area by Atwood Road and Marketplace Drive in Bel Air.
The $30 tent belonged to two men, according to the Fire Marshal's notice of investigation, which states the fire was caused by an open-flame heating device that ignited nearby combustibles.
Five firefighters from Bel Air Volunteer Fire Company took 15 minutes to control the blaze, the Fire Marshal's Office said.
Aegis staff member Allan Vought contributed to this article.