15 year old Miller G5 93% AFUE Gas furnace and home pressure issues

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  #1  
Old 12-24-16, 12:16 PM
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15 year old Miller G5 93% AFUE Gas furnace and home pressure issues

Ok,

Here's the house specifics-

Michigan, zone 5 for temp.

built in 1974-

Home is a 1200 sq foot ranch, 3 bedroom, central air with central cold air return with 1 additional return off the kitchen about 30 foot farther north. We have a partially finished basement of the same size that is accessed from inside the house off the kitchen. The rim joists have been insulated, currently The attic has approximately R-35 which is blown in (We plan to go to R55 in 2017) and have higher end wood framed double pane Anderson windows about 10-12 years old. 3 years ago it was Vinyl sided. Last year we converted the LP furnace to Natural Gas as it became available. The home has a chimney thats blocked off in the basement for an add on wood stove thats at my disposal which I will explain in a moment.

We have what we believe are a combination of 2-3 problems giving us heat and air issues- Negative air, as if we close the basement door/and or close the small basement windows the furnace will stop running. I installed a concentric vent and that at times it seems to help and others it has kept the furnace from being able to ignite.

My first question is can I reduce the 8" chimney via ducting to 4-6" and with adding a damper attach it to the cold air return for some make up air? I feel like this should alleviate a good share of my overall problems. I plan to track this as I progress and as it shakes out to the end result.

thanks in advance. long time no see! Grady and Crew

Ravin
 
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  #2  
Old 12-24-16, 06:14 PM
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I find it hard to believe a house built in 1974 is that air tight.

can I reduce the 8" chimney via ducting to 4-6" and with adding a damper attach it to the cold air return for some make up air?
What ??

Are you talking about bringing fresh air down the chimney ?
 
  #3  
Old 12-25-16, 05:09 AM
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I half considered the idea- the chimney not used for several years is still there and comes down into the basement and is about 24" away from my gas furnace. Its just sealed off with tin and duct tape.
A unwise idea to re-purpose it this way?

I would agree i didn't think that this house would be that tight but if I open the small 4" x 8" basement windows the air sucks in.

On a possibly related note- I have had times this year when the 2 pipe vent system is hooked up that the burners would not light with gas on and looking at the igniter glowing full tilt. I remove the air intake to the furnace, in effect turning it into a 1 pipe system, and cycle the unit again and it fires right up. I believe that particular issue is or involves the inducer, but that is just a guess.
 
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Old 12-25-16, 09:46 AM
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I've seen this happen when the vent piping is too small. If the furnace is vented with 2" pipe, often increasing it to 3" will fix the problem. This is especially true if the vent is marginal to begin with. Manufacturers will often say a 2" vent is ok for up to 75,000 BTU but only with a short vent run & only 1 or 2 ells. Any more than that & you need to go to 3".
 
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Old 12-25-16, 04:50 PM
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I swapped it from 1 pipe to 2 pipe- so let me ask this

for combustion air I do not have a good way of supplying 3" fresh air to the furnace, and the 2" exhaust is pretty much the same configuration it has been right back to the original install when it was LP.

With that said here's a couple of questions:

Arrange the inlet pipe for the fresh air intake to 2-3" above the furnace air intake. This should allow it to take whatever it needs from the basement like it has and the past and some fresh and get rid of the marginal inlet air for combustion - in the course curing potentially my differential pressure switch issues. the outlet is 2" off the inducer and quite literally is the same path its always been just adjusted I.E. the penetration thru the house converted to a concentric vent from 2" PVC.

Any thoughts on using the old chimney for some additional makeup air? seems that it or we could use some.

I recall in the old farmhouse I lived in and spoke to you guys before we discussed a 2 pipe vent out of PVC that went close to the floor for makeup air? is this a better idea yet again?
 

Last edited by Ravinmad; 12-25-16 at 05:48 PM. Reason: pressure equalization
  #6  
Old 12-26-16, 10:34 AM
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How many BTU is the furnace? What is the configuration of the vent system (length of pipes, number of 45 & 90 degree ells)?
 

Last edited by Grady; 12-26-16 at 10:47 AM. Reason: Additional question
  #7  
Old 12-26-16, 01:02 PM
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80k btu- vent rises straight up off the inducer about 52" to the ceiling then directly connects into standard 90 which is followed by another standard 90 (to transition from south to east)this run goes 40" before one last standard 90 transitions into straight 4' into the concentric vent to the outside-
 
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Old 12-26-16, 04:08 PM
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Last year we converted the LP furnace to Natural Gas as it became available.
Did a local gas company tech (or other pro) do the conversion and perform the appropriate tests/tuning? Related and more to the point...did you have these air/pressure issues prior to the conversion?
 
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Old 12-26-16, 05:08 PM
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I would gladly wager significant dollars a 3" vent system (intake & exhaust via a concentric) would fix your problem. I can't tell you how many times I've seen it.
 
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Old 12-27-16, 07:05 AM
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3" venting

so can I plumb 3" pipe up to the concentric and attach to it with 3'-2" reducers? and for the supply do the same- it comes out of the wye 2" but I'd just couple it up to 3" and run that to the furnaces intake? I also believe I can reduce the total number of 90's and such by going 45 degrees towards the vent and across the floor joists on an angle versus parallel, etc. with the pipe and then couple it with 45's and the reducer up to the concentric outlet which would reduce the final few feet back to 2"

For the price of a 3" cvent unit I could make a 2 pipe 3" system out of it all I'm thinking.

I also had forgotten that the tub piping access has air pulling directly from the attic and I never did anything with that- found that post from an earlier discussion we had- just like I never got around this past year to an energy audit

Here's our old thread

http://www.doityourself.com/forum/ga...ased-home.html
 
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Old 12-27-16, 07:10 AM
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I did the test and tuning, 3.5" WC on the regulator- correct NG orifices, DELTA T is good and matches the name plate. I am not a dedicated HVAC tech, thou I do work with them quite a bit, what I do is instrumentation on process equipment all the time-so all the tuning and measurements are items i am quite familiar with. the only thing I did not have or do was the combustion NoX analysis.
 
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Old 12-28-16, 07:45 AM
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Regarding the 3" vent system: You would need to make the change as close to the furnace as possible & run 3" all the way to a 3" concentric.

With your existing vent system, make sure the pipes are sloped uphill away from the furnace at a minimum slope of 1/4" per foot of run with NO droop or sags. A very small amount of water in the pipes can, & often does, create problems in a marginal vent system. There is no such thing as too much slope.

3.5" WC at the regulator is too low. Normally you want that reading at the manifold (outlet side of the gas valve).
 
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Old 01-02-17, 04:30 PM
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sorry for the late/slow reply but i did find the 2 cold air returns at the far end of the house essentially plugged. I pulled both grates, vacuumed and cleaned them along with the central return air grate and installed a new filter. Since this time I have not had any problems....could having insufficient return air caused part of the problems I was having?

I still need to get the blower door test done this spring and some passive air venting installed- The cost of a HRV i'd be more likely to replace the entire furnace unit with a new one given the rebates
 
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Old 01-02-17, 04:44 PM
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With what I posted earlier, I'd like to hear suggestions on what the team here recommends or suggests for a new furnace and central air/ heat pump combo. I'm in Michigan as I stated, and have just installed NG so I will not be going all electrical so I have no clue if a heat pump for cooling season makes sense or not.

I am looking to have a blower door test or a complete HERS index test. Locating exactly who to do what energy audit testing and what all is easier said then done.

Guys, whats your suggested Brand, model? If things work out to replace it all it would be professionally installed and bid by 2-3 local highly reputable local HVAC companies.

So be it Rudd, Rheem, Carrier, American Standard or some other brand of unit- Single stage, 2 stage, or modulating. I am a fan of lifetime warranties- I'm also considering a new hot water heater if someone wants to throw 2 cents in on that as well.

The only company I have some reservations about is TRANE well- Its doubtful if I'd go their route given the cost and they have you by the short hairs.
 
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Old 01-02-17, 05:36 PM
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Brands-
https://www.angieslist.com/articles/...vac-brands.htm

When I do my system, in the next couple years, it'll probably be Arco Air for the sole reason that the distributor is about 15 minutes from my house so I can run and get parts easy.
For efficiency, well modulating heat and variable speed motors are nice but I prefer the KISS method. A basic 90+ furnace that, aside from a cracked heat exchanger, can be made to run with generic parts from any supply house.
 
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Old 01-02-17, 06:42 PM
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KISS concept

I do love the KISS principle- sometimes the flashy lights and metal distract from what really matters!
 
  #17  
Old 01-03-17, 11:45 AM
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Arco air I cannot even see a listing for Michigan- 🤔
 
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Old 01-04-17, 02:21 PM
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Don't be concerned about brands. Be concerned with the quality of installation & parts availability. For my money there isn't 5 cents worth of difference from brand to brand.

I would much rather have the "cheapest" piece of equipment installed by the best installer than the "best" equipment installed by some jackleg.
 
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Old 01-13-17, 06:45 PM
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G5 Intertherm or Nordyne and other names

Ok, I just finished furnace fight with a G5 Intertherm. This furnace is in a rental. A few years back when propane was high in price I installed an electromate plenum unit. Now propane price is cheaper and my renters want to use propane again.
With electromate all you need to do is set the switch to bypass and cycle power. Now the furnace is set back to run propane again.
The thermostat calls for heat, inducer blower runs, manometer switch makes, gas valve clicks, no flame....? Process repeats to lock out.
Now I remove the combustion chamber cover and try again. It lights up just fine. I put cover back it stays lit up. I cycle it again with cover on, no flame again.
I tried several things. I checked the PVC flues, they were clear.I changed inducer blower thinking the bearing in motor may be causing it to be slower and with cover on , not moving enough air. That was not it. I changed gas valve and confirmed supply and manifold gas pressures. All good.
After about 3 evenings of this fight I decide to try moving the ignitor closer to the edge of first inshot burner. Put cover on and tried it. One burner lit up. Ok now, no crossover to other burners, no flame getting to flame sensor rod. I pulled the manifold out and checked offices again all clear. I removed the entire burner assembly...
Bingo rusty burners... crossover passages clogged.
I ordered new burners from Supply House. It works like new now. Evidently with that cover off, the propane would swirl enough and get ignition.
I'm an electrician of 37 years. I've seen alot of crazy things. This was a good one. Learn every day!
 
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