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## Summary:

- A ventilation standard for unflued gas appliances appears to give unsafe ambient levels of carbon dioxide. I need someone to check my calculations.

Unflued gas appliances emit all of their combustion products into the room in which they are installed. In the UK, ambient carbon dioxide in the commercial workplace is limited to 2800 ppm.

The UK/European standard BS EN 13410 (and many appliance manufacturers) give the formula for mechanical extract ventilation for unflued radiant heaters as: Extract flow rate (cubic metres per hour) = 10 x Net heat input (kW)

Consider a 20 kW heater installed in a space of 900 cubic metres. The required extract ventilation will be 20 x 10 = 200 cubic metres per hour. This equates to 200 / 900 = 0.22 air changes per hour.

In terms of gas rate, the appliance burns approximately 2 cubic metres of gas per hour. For natural gas appliances, cooled carbon dioxide production (by volume) is approximately equal to gas rate.

At equilibrium, room carbon dioxide will be: Carbon dioxide production rate / (Air change rate x Room volume)

In this example we get: 2 / (0.22 x 900) = 10,000 ppm - far in excess of the 2800 ppm limit. In a smaller room the problem would be worse.

Are my calculations correct? And, if so, how can the ventilation formula given in BS EN 13410 be correct?

The UK/European standard BS EN 13410 (and many appliance manufacturers) give the formula for mechanical extract ventilation for unflued radiant heaters as: Extract flow rate (cubic metres per hour) = 10 x Net heat input (kW)

Consider a 20 kW heater installed in a space of 900 cubic metres. The required extract ventilation will be 20 x 10 = 200 cubic metres per hour. This equates to 200 / 900 = 0.22 air changes per hour.

In terms of gas rate, the appliance burns approximately 2 cubic metres of gas per hour. For natural gas appliances, cooled carbon dioxide production (by volume) is approximately equal to gas rate.

At equilibrium, room carbon dioxide will be: Carbon dioxide production rate / (Air change rate x Room volume)

In this example we get: 2 / (0.22 x 900) = 10,000 ppm - far in excess of the 2800 ppm limit. In a smaller room the problem would be worse.

Are my calculations correct? And, if so, how can the ventilation formula given in BS EN 13410 be correct?