Free Ruud/Rheem furnace


Old 09-17-08, 09:37 PM
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Free Ruud/Rheem furnace

I have an old oil burner converted to gas (50% eff.) and I recieved a free Ruud furnace (UGFD10EZCMS) and would love to install it as it's a modulating 90% eff furnace, only it's too big.

I took the burner apart and pulled off one of the jets and it's a number 50, anyone know of a source for smaller ones? I could just braze it and re-drill but to what size? I need about 60K BTUH and this furnace is a 102K.

Also if I put in smaller jets will that work? It seems that should be simple enough. Any thoughts? Oh and the furnace is 42K min which is fine but it would be nice to modulate down to 20-30K...
Thanks for any advice!
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Old 09-18-08, 01:52 PM
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If only it were that easy.

Back in the olden days, before induced draft fans, you could change the firing rate by changing the burner orifices. The burners had primary air shutters you could adjust and the secondary air was simply not considered that much.

But the modern burners have a calibrated orifice on the intake to the induced draft fan along with control of that fan (2 speeds for 2 stage burners) that precludes the easy ability to significantly change the firing rate. Any change of the burner orifices without a corresponding change of the induced draft fan inlet orifice will seriously upset the combustion and will at the very least reduce the combustion efficiency of the unit. It would void any warranty (maybe not important to you) and would void any EPA certification.

Furthermore, reducing the BTU input by some 40% will have serious repercussions on the heat exchangers and would require a significantly lower amount of air to be blown across the heat exchangers to have the requisite minimum temperature rise. Lacking that temperature rise would increase the likelihood of condensing in the primary heat exchanger with subsequent increased corrosion.

Any way you look at it the end result is bad and your "free" furnace will end up costing you more money in the long run than simply purchasing the proper sized furnace in the first place.
Old 09-19-08, 03:56 AM
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Nice Furnace

Premium Ruud Brand Gas Furnaces

Ruud is a Rheem Corporation Company. This an award winning furnace was rated a "Best Buy" by a leading consumer publication. This Ruud gas furnace is loaded with features like the Contour Comfort Control featuring the High Efficiency Modulation Function and 2-stage gas valve that slows furnace capacity to as little as 40% for greater comfort and maximum energy savings. And this model features the variable speed ECM2+ motor for the greatest comfort levels and lowest sound levels possible.

This is Ruud's most feature rich model and is their top-of-the-line offering. And at an efficiency level of 92% high gas bills are a thing of the past. Off season quantities are very limited and like summer, when they're gone, they're gone forever.

Furnace Model - UGFD10EZCMS
Heating Input - 105K Btu
Heating Output - 100K Btu
Efficiency - 93%
Blower Capacity - 5.0 tons
Airflow Configuration - Upflow
AC Ready - Yes
Noise Reduction - Yes
Gas Type - Natural
Factory Warranty - Yes

2 stage gas valve with one stage running furnace at 40%.
Thats 40,000 BTU. This furnace isn't too big even at 100,000 BTU. I.d stick it in. What does too big mean anyway. It won't be any less efficient because its bigger than you need.
Old 09-19-08, 01:24 PM
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I have been thinking, I sould leave the oriface size alone and just plug 3 of the 7. That way the temp stays the same in the ones that are being used and the mixture will be the same also (I think). and 4 out of 7 working gets me just under 60K which is what I need. Any thougts on that?

The furnace was used but free to me, I don't have a warranty or anyway to exchange it. I would rather make this one work with all the cool functions it has than sell it on Craigs list and buy some normal one.

I plan on firing it up in my back yard today and measuring the manifold pressure with all tubes running and then with only 4 going. Being an engineer at heart, I live for data...
Old 09-20-08, 01:22 PM
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I wouldn't plug them.. Just get a matching Mod stat, and let the stat fire the furnace as needed, if I recall there is a sensor in the system that will see if it starts over heating, the burners will mod down to a lower BTU output.
Old 09-20-08, 08:50 PM
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Thanks for your input, and that was my first plan but it may short cylce even after "learning" my house and it would heat my house quickly but not as efficiently. I have the Mod Thermostat and would like to mod down to 24K btu (42/7x4) instead of the normal min. input of 42K. That would allow a longer burn at lower temp and run as it should. Make sense? I'm just learning all this but this furnace is amaizing the way it does what it does. The hardware is simple as any other furnace but the computer part that modulates is worth it's weight in gold... Anyway I can easily unplug the 3 burners and do what you said. The hard part was remounting the over temp sensors to the active burners and the sensor that is on the last burner to be lit to sense a complete start up. Not to mention pulling out of the house the old oil burner from 1945 that was bigger than my fridge and 300lbs!
Old 09-20-08, 08:56 PM
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Your furnace will die an early death of the existing duct system isn't sized to handle the airflow of a 100k+ output furnace.

A poor installation can result in carbon monoxide poisoning, fire, explosion, or worse. I would sell the oversized Rheem unit and find a trustworthy HVAC contractor to get the job done. Not worth the safety risk.

If you already installed it, at the very least get it inspected.

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