Ventilation question

Robert Tyrrell · Feb 20, 2014

I've just been to a house (Not a job) that has a gas bbu with a radiant fire on the front and I'm convinced that the free air isn't enough but I'd like to check with anyone that has a bit more know how when it comes to working these things out.

The unit is a Myson Housewarmer 30/45 with an unnamed radiant fire on the front. It's a lined brick built chimney btw. The room is approximately 18 feet by 16 feet and currently their's a 65 cm2 free air vent in the corner of the room that vents directly to outside.
I've worked it out like this:
45KW (Gross) ÷ 1.11 = 40.5 KW (Nett)
40.5 + 5 = 45.5KW nett total heat input
45.5 = 5 = 227.5 cm2
227.5 - 35 (Adventitious) = 192.5 cm2

There is a free air vent that states it's 65 cm2 so that leaves another 127.5 cm2 that's needed to make this place safe, or am I missing something?

Any advice on this would be great.

heliotrope · Feb 20, 2014

What you have got completely wrong is your Kw inputs for this appliance.

It would be an enormous bbu and fire, 45 Kw is way over the top.

The total for this appliance would be around 15 Kw give or take a bit
without looking up the installation instructions.

Get a look at the data plates for total Kw.

kirkgas · Feb 20, 2014

These back boilers are usually 14-17kw, plus the fire (5.5-7) so your calc is way out, so 65cm2 won't be far away, you need to look at both data plates, add them, divide by 1.1 - 7 for adventitious them x 5
Why have you quoted room size? It's not relevant unless it's under 5m3 then it's classed as a compartment

kirkgas · Feb 20, 2014

I'm not sure about the myson bbu's but the 30/45 could be the output/input in 1000's of btu's ( so input is 45,000 btu's, so divide 45,000 by 3412 to convert it to gross kW input

Robert Tyrrell · Feb 20, 2014

kirkgas said:
I'm not sure about the myson bbu's but the 30/45 could be the output/input in 1000's of btu's ( so input is 45,000 btu's, so divide 45,000 by 3412 to convert it to gross kW input

Cheers matey. That's what's wrong. I knew something was amiss but couldn't work it out in my head. It defo states on the data plate something about 45 but the rest is all messed up. Thinking about the age of it, it has to be but not kW.
And for those who would like to know - I chucked in the room size because J was also cleaning samurai swords at the same time and just didn't think.