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Frequently Asked Questions
Why is it so efficient?
Nothing is lost up a flue.
There is no flue at all.
No heat has to cross a metal wall.
Effectively all the fuel energy reaches the space.
Equipment is simpler and cheaper too.
Over a season the difference is substantial.
What enters the building with the heat?
The products of combustion.
Water vapour and carbon dioxide principally.
Small quantities of other products as well.
All of it goes into the supply air.
Dilution keeps concentrations within limits.
That is why minimum airflow is designed in.
Where is it permitted?
That depends on jurisdiction and occupancy.
Industrial and process spaces are typical.
Sleeping accommodation is usually excluded.
Healthcare occupancies generally are too.
Rules differ by country.
Establish the position before designing.
Why is the airflow interlock fundamental?
Combustion happens in the airstream.
Reduced airflow concentrates the products.
It also overheats the burner section.
Proof of airflow must precede firing.
This is not an optional accessory.
Test it at commissioning.
What does the added humidity do?
Raises moisture in the space.
Combustion produces water vapour.
In a dry winter that is welcome.
Where humidity is already high it is not.
Condensation on cold surfaces can result.
Consider the space's moisture balance.
How does it compare with indirect firing?
Efficiency and cost against air quality freedom.
Direct wins clearly on both running cost and capital.
Indirect delivers clean air anywhere.
Direct is restricted by occupancy.
Where permitted, the economics favour direct.
Where not, there is no comparison to make.
What maintenance does the burner need?
Regular inspection and cleaning.
It sits in the airstream and collects dust.
Combustion quality must be checked.
Poor combustion changes what enters the space.
Filtration upstream protects it.
Service intervals are usually specified annually.