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Old 09-13-2010, 03:19 PM   #31
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In Trouble need 150,000 BTU's


Had two contractors out both said opposite things,
guys one, wants to put in 2 units with 2 stage motors, 80,000 btu's each.
guys two wants to put in one 95% unit(lennox G71MPP0 with what he called a mogillating (not sure of spelling) continuos motor, he said he guarantee's it will do the job, he also said you cannot have 2 units with both 2 stage motors and have then run in sink, now I'm more confused, everyone says they are right, but no one agrees.

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Old 09-13-2010, 03:43 PM   #32
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In Trouble need 150,000 BTU's


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Originally Posted by turbomangt View Post
Had two contractors out both said opposite things,
guys one, wants to put in 2 units with 2 stage motors, 80,000 btu's each.
guys two wants to put in one 95% unit(lennox G71MPP0 with what he called a mogillating (not sure of spelling) continuos motor, he said he guarantee's it will do the job, he also said you cannot have 2 units with both 2 stage motors and have then run in sink, now I'm more confused, everyone says they are right, but no one agrees.
BIG NO ON MODULATING FURNACE! Same for two stage furnaces.

THEY CAN NOT BE TWINNED OR USED IN TANDEM.
Modulating and two stage furnace blower motors will not run at the same speed consistently which is necessary to prevent the individual blowers from over powering the return air ( that could be said better but that's the best way I know how to put in plain terms).

Yuri you are the resident lennox expert. How about a little input?
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Old 09-13-2010, 03:54 PM   #33
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In Trouble need 150,000 BTU's


[Edit]After HVA's kind words below, I thought harder.... I can't find the article I was referring to, but on reflection I think it was about sizing AC units not furnaces. I'm still curious if anyone has done a J-manual load calc as opposed to a thumbnail guess.[edit]


A lot of comments about "load calc".

So these guys come over, eyeball the existing unit, and just sort of look around, then say "you need ___x____ BTUS", right? I mean, did anyone ever spend considerable time inspecting the building and punching numbers into the load calc software?

If that never happened, then there is a very strong chance their eyeball guesstimate is 'way more BTU than you need. There was a good article in FHB magazine awhile back. A common practice is for contractors to size HVAC gear for the extremes of the location. But that's only for a very small number of days in the year. The rest of the time they cycle off and on in some way that is inefficient. I forget the tech reason its inefficient hte rest of the year. The eyeballing-style contractors do that to make sure the customer is comfy and prevent complaint calls that one or two days each year that hit the extreme temps. The author argues that the CORRECT BTU output is for based on need during the bulk of the rest of the year. Anything else, they said, was oversized and inefficient.

So.... if you are able to swing it.... consider a real load calc for the building as-is, and then tweak it for various insulating/sealing/venting upgrades. That might shed a lot of light on your options and best bang for buck.

SteveEl

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Old 09-13-2010, 04:25 PM   #34
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In Trouble need 150,000 BTU's


Clover is right. May not be too pretty but he knowz hiz stuff. I just checked the Lennox G61V and the G71MPP and neither has a twinning terminal on their circuit boards for the reasons he said . I would use 2 G51's and get a PROPER heat loss calculation done to buy the correct sized units. NO eyeballing in your situation. Lennox makes an optional twinning kit for the G51. Very good tried tested and true furnace, no fancy bells or whistles, easy to fix and get parts for. I have one in my house.

Good Luck
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Old 09-13-2010, 04:26 PM   #35
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Originally Posted by steveel View Post
A lot of comments about "load calc".

So these guys come over, eyeball the existing unit, and just sort of look around, then say "you need ___x____ BTUS", right? I mean, did anyone ever spend considerable time inspecting the building and punching numbers into the load calc software?

If that never happened, then there is a very strong chance their eyeball guesstimate is 'way more BTU than you need. There was a good article in FHB magazine awhile back. A common practice is for contractors to size HVAC gear for the extremes of the location. But that's only for a very small number of days in the year. The rest of the time they cycle off and on in some way that is inefficient. I forget the tech reason its inefficient hte rest of the year. The eyeballing-style contractors do that to make sure the customer is comfy and prevent complaint calls that one or two days each year that hit the extreme temps. The author argues that the CORRECT BTU output is for based on need during the bulk of the rest of the year. Anything else, they said, was oversized and inefficient.

So.... if you are able to swing it.... consider a real load calc for the building as-is, and then tweak it for various insulating/sealing/venting upgrades. That might shed a lot of light on your options and best bang for buck.

SteveEl

Excuse me while I wipe the excrement from shoes I stepped in from your post.

Do not attempt to confuse the OP further. He already knows a load calc needs doing.

If you had any credentials you sure invalidated them with your post.

You're saying if, say in Mi, the design temp is five degrees and the load calc says a 60kbtu furnace is required, the home would not need so big a furnace because it seldom gets down to five degrees.

Horse Hockey Pucks!

You get OD ambient of 20*F with a strong wind blowing you are going to need every bit of that 60Kbtu of heat.

Three thing effect the speed of heat transfer: size, temp difference, and BTUH content.
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Old 09-13-2010, 04:43 PM   #36
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Turbo, can you take a half dozen or more pics of the furnace and ductwork so we can see what it looks like. May need modifications to the return duct and we would like to see what you have now to help better. Post them at photobucket and put the links here or make small jpegs and post them here.
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Old 09-13-2010, 04:46 PM   #37
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No VS blower unit, no matter what brand it is, is approved for twinning. proper twinning requires that both units be single stage units. And PSC blowers.

A mod can serve you well on your duct system. Since it has low static in its lower modulations. it tends to have more air come out at the far registers, then at the near registers.
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Old 09-13-2010, 04:50 PM   #38
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I would think that mods would come with variable speed blowers?? The Lennox does. Not sure about York. Very finicky furnaces the mods. I would stay away from twinning them.
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Old 09-13-2010, 04:53 PM   #39
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I would think that mods would come with variable speed blowers?? The Lennox does. Not sure about York. Very finicky furnaces the mods. I would stay away from twinning them.
u read my mind.
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Old 09-13-2010, 04:58 PM   #40
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I didn't say to twin a mod.

I doubt his house really needs near as much heat as some of those contractors think/say it does.

Thursday, I was at a hose that had a Goodman GUN125-5 furnace. Sure did make that 2200 sq ft house warm. When it wasn't tripped on its high limit. oh, and it had a 2 ton A/C also. Sure did make for some hot air coming out of the registers.
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Old 09-13-2010, 05:06 PM   #41
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What is the largest size in BTUs mod that York makes? The Lennox is 135,000 in the G71 and SLP.
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Old 09-13-2010, 05:13 PM   #42
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120,000 input. Gives you 116,000 output.

Comes with a 1 HP VS blower.
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Old 09-13-2010, 05:17 PM   #43
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Would be REAL interesting to know what actual size he needs if someone did a heat loss calculation.Load Calculator
The newer larger units can do 5 tons of AC no problema with the blowers they put in now.
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Old 09-13-2010, 05:23 PM   #44
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It doesn't take a lot of work or money to knock 10,000 plus BTUs off of the heating load of a house.
And the larger the house is, the more you can know off.
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Old 09-13-2010, 05:33 PM   #45
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Originally Posted by turbomangt View Post
Had two contractors out both said opposite things,
guys one, wants to put in 2 units with 2 stage motors, 80,000 btu's each.
guys two wants to put in one 95% unit(lennox G71MPP0 with what he called a mogillating (not sure of spelling) continuos motor, he said he guarantee's it will do the job, he also said you cannot have 2 units with both 2 stage motors and have then run in sink, now I'm more confused, everyone says they are right, but no one agrees.
The Lennox guy is right. That's why I stated standard blowers in the first post because you can't twin v-drives or multi stage equiptment. If he's willing to put that guarantee in writing go for it. One G71 will be much cheaper then 2 furnaces twinned up front and in the long run.

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