Direct fired greenhouse heaters

[MattWeth]

I was at a customer today servicing five cabinet heaters (40 degrees in the greenhouses, had to turn the stats up to 50 to get them to fire, so then I'm in a 40 degree greenhouse standing next to a heater trying to make it 50 - mad or what?!).

Anyway, he mentioned that he also had a few direct heaters that he'd like to get back into service. The best candidate to start with had a Riello with a failed oil pump. Simple I thought - chuck a new pump on and set it up. And then I thought, how the hell do you gas check one of these? The burner fires directly onto a blast plate and there's a flipping big fan behind the burner adding a load more air.

Where do you analyse one of these or is it all by feel?...

 

[lame plumber]

you follow the manual or you shouldnt be touching it according to the regs. the other thing to do is to get yourself proven as gas safe on here and ask on the private forum

 

[Dotty]

Are you asking about fga'ing it?

Because gas rating an oil fired appliance...... Well it just don't make nooooooo sense!

 

[MattWeth]

Sorry chaps - I was talking about flue gas analysing (or otherwise setting up a new oil pump) on an oil fired direct combusting greenhouse heater (blows its flue gasses into the space along with extra air from its fan).

There is no manual, data plate or even a manufacturers name. These things have been in service in a farm for 30 years.

Why do I want to get myself 'proven as gas safe' when I don't do gas and am asking questions about an oil fired heater in the oil forum?...

I'm a fully Oftec qualified boiler engineer.

 

[Dotty]

Sorry chaps - I was talking about flue gas analysing (or otherwise setting up a new oil pump) on an oil fired direct combusting greenhouse heater (blows its flue gasses into the space along with extra air from its fan).

I'm a fully Oftec qualified boiler engineer.

With all the doors open would be my first thought!

You got an expendable apprentice to hold the probe?

 

[MattWeth]

With all the doors open would be my first thought!

You got an expendable apprentice to hold the probe?

There's nowhere to put the probe - that's the problem They're a two foot diameter tube with a burner in the middle and a big fan at the back which blows past the burner and adds extra air to the burners output...

They're not uncommon in greenhouse horticulture - plants like CO2 you wouldn't want to be shut in the greenhouse for any length of time with them though (even servicing and test firing them rapidly gets unpleasant).

The best advice I've been given is go for a decent flame colour and no visible smoke.

 

[Dotty]

Use one of these to hold your probe in place.

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[MattWeth]

Use one of these to hold your probe in place.

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It wouldn't matter how the probe was held - it would be sampling the combustion gasses + a load of extra air from the fan directly behind the burner so any flue gas analysis would be worthless...

 

[Dotty]

Not entirely. What you should be looking for is co level.

 

[lame plumber]

which is what lots of american pig farmers failed to do in keeping their piggies warm but ended up gassing 1000s using warm air blowers!!

 

[kimbo]

A picture might help. Powrmatic do warm air blowers for factorys might be worth giving them a call to find out what make it is. I have a custlomer who has just bought one of these from a garden centre but there is a flue attached to his.

 

[Dotty]

Powrmatics are indirect, warmflow do a a range too.

Funny, I'm comfortable with gas direct fired heaters but not oil ones!

 

[MattWeth]

A picture might help. Powrmatic do warm air blowers for factorys might be worth giving them a call to find out what make it is. I have a custlomer who has just bought one of these from a garden centre but there is a flue attached to his.

Yep - I'm familiar with the Powrmatic cabinet heaters - the five I just serviced were Powrmatics. These direct fired heaters aren't Powrmatic - the customer tells me that the company who made them went out of business 10 years or so ago.

Haven't got a picture unfortunately but they're very simple - imagine a 2 foot diameter tube about 5 feet long with a big propeller fan at the back blowing forwards out of the tube. About half way down the tube, there's a box underneath containing a burner with the blast tube poking upwards through the wall of the tube angled forwards towards the discharge end of the tube. Inside the tube there's an 8 inch diameter heavy steel plate suspended so that the flame hits it. There's a control interlock which only powers the burner when the main fan has been running for 15 seconds and the whole thing is controlled by a simple thermostat in the middle of the greenhouse.

Regarding the flue gas analysis of these direct fired heaters - any CO ppm reading will be affected by all the extra air from the blower fan which is directly behind the burner blast tube (the products of combustion will be massively diluted by the extra air). So I don't see how you can get a meaningful reading.

As these things are inherently unsafe perhaps it just doesn't matter as long as its not producing smoke and soot?...

 

[Dsgas]

Try contacting Riello ,they may have a list of the appliances you are talking about on a database and can give you some figures to work with.

 

[Dotty]

Yes Matt, the co will be diluted. Doesn't mean it's at a safe level though!

I always do a room test with direct fired appliances for my own peace of mind. I'd rather you faff about with the diluted readings until they're acceptable rather than pray they're right then see you prosecuted!

Don't want that mate!