How the variable firing rate gas valve works.

[@petersamios5409]

Awesome presentation. Thanks for the information.

[@airsysinc.7517]

How the control works on this valve

[@MSKChess]

Looks similar to the gas valves we have in Europe. They are modulated by boiler (furnace) potentiometer (controls) and NTC thermistors which send signal back to PCB to modulate the gas depending on the parameters set. Some old boilers still only have a two stage low and high flame setting.

[@glasser2819]

interesting to know. It must be a good old German design 😃

[@MSKChess]

@@glasser2819 Actually our valves have changed to a zero governor which as you know relies on negative pressure from the fan. The faster the fan the more negative pressure and the more gas mixes in the venturi. Its much more efficient than a modulating valve based on solenoids. European boilers have an efficiency ratings of around 95% because of condensing technology. No one uses open flued boilers anymore in domestic properties, they are all room sealed.

[@glasser2819]

excellent explanation of the manifold gas pressure modulation. Thank you for sharing your in-depth knowledge of these design evolution, "GF" 👏

[@grayfurnaceman]

Welcome GFM

[@hvacdoc2338]

GFM !! A man with a wealth of knowledge !

[@grayfurnaceman]

Yes, my wealth runneth over. lol GFM

[@glasser2819]

yes GFM is a true Master 😃

[@jameswestii454]

Great video once again. I have a gas valve that is White-Rogers Model 36J22Y-204. I says to back outlet pressure test screw out one turn counter clockwise then attach 5/16” hose over boss. Is there a reason to do this compared to removing screw and inserting barb fitting?

[@ronieronnwick8411]

Forgot to say that the ac company pulled the large 'range' fuse completely and wired everything to 2 60amp barrel fuses before the round fuses. Thanks again.

[@grayfurnaceman]

If you do have a true "fuse box", no breakers, you need an electrician to replace it with a breaker panel. I would get an electrician to check this one out. GFM

[@ronieronnwick8411]

I figured it out. Was a barely loose fuse mounting screw. Barely wiggled, but just enough to cause issues. Thank you for the reply

[@Twentytwo22-entertainment]

Congrats on 100k!

[@grayfurnaceman]

Thanks GFM

[@Jon-hx7pe]

What happens when the modulating furnaces are installed in areas with low heating value natural gas and or high elevation? For normal furnaces some of the manufacturers say to use a gas pressure other than 3.5, they have a range for minor adjustments. For units with this style modulating valve, looks like you can do that and only the orifices can be changed if approved by the manufacturer.

[@grayfurnaceman]

All I can tell you is manufacturer's instructions. GFM

[@ronieronnwick8411]

I had my furnace replaced about 3months ago, runs fine. Kicked on my central air a few times, seems fine. I go to kick it on yesterday and nothing.. I followed lack of voltage to fuse box (older style Federal brand), the fuse is only reading 42 volts. Replaced all of them. Is the fuse box bad? Noburn marks , wires are tight, everything seems good. Any help would be appreciated. Btw, you unknowingly helped me with furnace and its bad heat exchanger. Thanks

[@Jshortca]

I've replaced a dozen of these things on Rheem modulating furnaces. Not sure why so many failed.

[@TheProletariat.]

So does the main board also control the speed of the inducer motor as well? I would think that to maintain proper combustion that draft would also fluctuate to compensate for a greater or less firing rate.. Great video!

[@Jimddddd1981]

Yes it does.

[@Rickmakes]

My furnace is variable from 35-100%. The inducer and blower are both variable EC motors.

[@grayfurnaceman]

The early ones (about the year 2000), used a 2 stage inducer, but the newer ones are variable speed. GFM

[@boby115]

Modulating gas valves are nothing new, we've been using them in the commercial boiler industry longer than I've been alive. The problem using them with forced air furnaces is temperature rise. The furnace manufacturers are having a hard time getting a handle on this. Heat exchanger failures on these type of furnaces I feel are at an all-time high, merely because the temperature rise is constantly varying. In the commercial boiler industry we have a handle on this because of stack temperature adjustments & boiler tube design. I feel the force air furnace manufacturers still have a way to go on this. Sometimes I feel built-in obsolescence is their game plan.

[@grayfurnaceman]

You need to be looking closer. The Rheem unit this valve came off of uses a return air temp sensor to determine gas flow. So much for the heat exchanger issue. You are correct that modulating is not new. Space heaters have used hydraulic controlled gas valves for over 50 years. Makeup air units for restaurants also use a hydraulic valve. GFM

[@boby115]

@@grayfurnaceman thank you so much for replying and addressing my concerns. I also wanted to thank you for your interest and dedication to the HVAC industry and the people you've educated over the years. I find your videos, experience and expertise unsurpassed on social media. I have been a first responder / service technician for the gas utility in St Louis, Missouri for 35 years. Our service department at Spire St.Louis is approaching 300 service technicians, all HVAC men and women from the superintendent down to the employee just hired. We keep meticulous records on every hazardous Appliance report we issued. Through statistics and experiences we can notice certain Appliance manufacturers that may be having issues. I think it may be premature for us to praise or condemn the particular heat exchanger you are referring to. When new technologies are introduced to the marketplace sometimes they lose their luster if problems occur. Only time will tell. Thanks again for your dedication and service to the industry over the years, Bob.

[@grayfurnaceman]

@@boby115 Reference the Carrier 58sx as an example. A high efficiency furnace with all the bells and whistles that had a reaction between plastics in the secondary and the stainless steel, causing massive numbers of leaking heat exchangers. Thanks for the support. GFM

[@glasser2819]

I am always thrilled when I see a cheap residential gas furnace stuffed in an attic "to save space"... knowing how a failed heat exchanger will lead to flame rollouts... So ultimately furnaces are a attic fire hazard yet pass the building code inspection 😂

[@gerrybasildon]

thank you

[@grayfurnaceman]

Welcome GFM

[@lee-johnson]

Nothing more than an actuator, but clever

[@grayfurnaceman]

I would call it an automatic adjustable regulator. GFM