# Infrared tube heater - condensate at what temp?



## acro (Jan 14, 2013)

I am finishing up a 24x40 shop with 14' ceilings and have a 125k btu tube heater - I actually have 3 of them with 50' tube for each and some elbows.

Fuel is propane. All tubes will be horizontal

So, I have about 150' total tube and reflector on hand. I want to maximize the efficiency. I believe the best way to do this is to install as much tube length as practical. No sense dumping too much heat out of the exhaust.

But at a certain point, the flue gasses will condense and form an acidic condensate. So how far can i push it? I am thinking that I will likely do 70' total.

Should I worry?

I have a similar question regarding a propane unit heater with "B" vent. Why not install more exhaust pipe, possibly single wall even, to get the most heat out of it before it exits the building?

I installed one for a buddy and only have about 3' of pipe before it goes out the wall. The exhaust is VERY hot at the rain cap. It just seems like such a waste.


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## Fouthgeneration (Jan 7, 2014)

Call the manufacturer for the O M or installation manual, Why reinvent the wheel?

The beauty of infrared heat is the radiant heat, any condensing heat would require additional fans, filters ducts and plumbing along with various safety switches/logic circuits.

To long of pipe would create a low air flow/ over rich jetting with the "stock" blower. 

I'd think installing one condensing furnace with 2 of the infrared would increase your shops heating flexibility and save more $ then a one off design.


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## acro (Jan 14, 2013)

I had not considered the jetting issue with increased pipe lengths.

I found my literature online and it says that the maximum allowable length of vent pipe is 60 feet. but it says that the radiant tube is not included in the measurement. and "vent pipe" must be insulated.

In the next paragraph, it says that the maximum equivalent vent length is 30 ft. Why the difference?

I just need to keep the flue gas above the condensing temp, which I would assume is below 212 degrees. Maybe there is no way to tell other than experimentation, but I just don't want to end up with flue gas with usable heat left in it.


For argument sake, could I assume that with 50' of radiant tubes, I could also have 30' of vent? Why not just have say 75' of radiant and 5' of vent.


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## beenthere (Mar 5, 2009)

The cooler the tube is, the less heat that is radiated.


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## Fouthgeneration (Jan 7, 2014)

The Vent part of the furnace is insulated to keep it above 212 degrees all the way to the top Hat.

Elbows,Tees, and other connector pipe will have an equivalent length of straight pipe to make the math almost idiot proof. Thus a short radius elbow might = 5 foot of straight 4" double wall.

It might pay to use stainless piping to avoid corrosion issues.

In floor hot water has most of the Radiant heat qualities if you are pouring the slab..

See if you can rejet/experiment on your buddies over fired unit....


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## acro (Jan 14, 2013)

beenthere said:


> The cooler the tube is, the less heat that is radiated.


Yea, but no sense radiating that heat outdoors.

I guess I will just do some checking with my head gun and see.


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## Fouthgeneration (Jan 7, 2014)

You could install a semi tractor intercooler to condense the stack gases if you have a floor drain to run the water to.
I'd check the cost of the install vs the fuel savings and loss of space.

possibly you could just run another 30 feet of 3"-4" pipe slightly downhill to a tee that the lower branch had a water trap drain for the condensate water and a vertical stack with enough draft to offset the added resistance of length and cooler, more viscose exhaust gas flows.

Another slightly more complex version would be to wrap the post radiant part of the inside piping with a larger pipe that was connected to the air inlet of the furnace at the hot end and out of doors at the cold intake, plumbing would still be need at the tee to vertical stack.

Plumbing the intake to out side air in any case will reduce fuel use/increase efficacy.


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## acro (Jan 14, 2013)

Now we're talking. I can get my hands on an intercooler pretty easy. I just figured on keeping the vent horizontal through the wall


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## acro (Jan 14, 2013)

Well, I found that the flue gasses should be kept about 300f to eliminate the condensate forming.

I need to finish up the wall penetration and take some temp readings.


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