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Frequently Asked Questions
What is a hybrid or dual-fuel system?
A heat pump paired with a combustion appliance.
Usually a gas or oil boiler, or a furnace.
A controller decides which one runs.
Both remain available at all times.
It refuses the choice other machines must make.
Why pair two heat sources?
Because their strengths are opposite.
The heat pump is cheap to run in mild weather.
It weakens as the temperature drops.
The burner is indifferent to outdoor conditions.
Each covers the hours the other handles poorly.
What is the switchover point?
The condition at which control hands over.
Below it the burner takes the load.
Above it the heat pump runs.
It is a controller setting, not a fixed property.
Where it sits defines the system's purpose.
How does a cost-based switchover work?
It compares running cost at the current conditions.
Heat pump efficiency varies with outdoor temperature.
Electricity and fuel prices are weighed against it.
The point moves as those prices move.
The cheaper source runs at any moment.
How does a capacity-based switchover differ?
It waits until the heat pump cannot meet the load.
Prices play no part in the decision.
The heat pump runs as long as it is able.
The burner covers only the shortfall.
Same hardware, different intention.
Why does this suit retrofits?
The existing distribution system can stay.
Emitters sized for hot water are already installed.
The boiler covers the conditions they were sized for.
No wholesale replacement is needed first.
It is a route in that the building can afford.
Can both sources run at the same time?
Some controls allow it, others do not.
Parallel operation covers a shortfall smoothly.
Alternate operation is simpler to control.
The strategy is set at commissioning.
It should match how the building actually behaves.