There were a lot of pot plants, not only on the second floor but even in the basement.
And if this hot house was like others that have exploded, illegal propane gas tanks were probably being used to speed the pots growth.
But the propane may have also fueled the explosion.
Sources tell Eyewitness News that Con Ed workers looking for a gas leak on 234th Street never picked up any measurable readings neither outside the home nor in the basement prior to the explosion.
That has investigators focusing on propane tanks as the possible source of leaking gas which caused the massive explosion that killed Fire Chief Michael Fahy.
"The explosion comes with great force," said Jim Bullock, NY Fire Consultants.
Former FDNY Fire Chief Bullock says besides smelling just like natural gas, propane can be more explosive.
It's been linked to marijuana grow house blasts in Florida and Colorado.
Bullock says the propane gas is used to fuel generators that enrich the air with carbon dioxide, essentially a greenhouse gas that accelerates pot growth, but if the propane leaks and ignites, it's like dynamite.
"That would cause a tremendous explosion. That's why in New York City, LPG or propane tanks are never allowed inside a building," Bullock said.
The NYPD has two men in custody: Julio Salcedo, who rented the home in the Bronx that police say was under investigation as a marijuana grow house; and 32-year-old Garivaldi Castillo, of Washington Heights, who is facing two counts of criminal possession of marijuana.
A source provided Eyewitness News with a picture of a van in the home's driveway.
Several times, he claims he saw big blue barrels unloaded from the van and taken into the house, possibly to hold liquid fertilizer which is highly flammable.
Only a few months ago, the Drug Enforcement Agency warned about the increasing threat of "grow houses" to first responders.
This DEA Intelligence Report stating, "Explosive materials such as propane and butane...pose clear hazards to firefighters or police officers responding to the residence in an emergency situation."
"There are fertilizers and chemicals present and those can lead to a combustible situation," said Jonathan Wilson, DEA Special Agent.
Wilson says marijuana hot houses are ticking time bombs often fueled by dangerous electrical wiring and jerry-rigged propane tanks.
"The propane is used for the CO2 converter that will increase the production of the lab, and that added to faulty wiring makes any indoor grow an accident waiting to happen," Wilson said.