Differences between 59MN7A and 59MN7B

[rminoak]

Hello everyone, first post and glad to find this forum.

Wondering if anyone could share the differences/changes/updates between the 59MN7A and the 59MN7B? I know the B is newer and the latest major series of the 59MN7 but wondering if anyone knows what the specification or technical differences are. Nothing jumped out at me when I read the product data of the A and B but maybe it's an oversight on my part.

I have an opportunity for a 59MN7A060V171214 and was wondering if I should be looking at the 59MN7B for my home instead since it is newer or because of possible known issues with the A version?

Thank you.

[Admin]

If you compare the spec sheets between the 59MN7A and the 59MN7B you will see the 59MN7B has lower amp ratings.

[Sergroum]

0.7 amp difference.  Hopefully it's more then that, hahah.  I'm yet to work on mn7B.  Are the parts from A compatible with B? Control boards, gas valves?  I'm guessing Blower motor and maybe inducer fans are different. 

[rminoak]

Thanks @Sergroum and @Admin.  I appreciate the info.  I was wondering that too.  Wondering if either of you might suggest if the A major revision or B would be the better way to go for me as the long term homeowner/end-user from a reliability point of view.  Sometimes the changes are better, and sometime not... for the homeowner that's planning on staying in the home a long while.  The shipping weight for the B was reduced by 6.5 lbs as well when compared to the A.  Just makes me wonder where that 6.5 lbs came from as well...  lighter case, frame, heat exchangers, ?  Can't see where else that would come from really unless the shipping packaging is included in that too which I don't know if it would be.  Same with the assumed changes in motors and possibly boards that lowers the ampacity of the unit by 0.7.  Good changes? or better to get A?

If you have any other insight or if any other carrier guys do, it would be much appreciated to help me decide.

   

[Sergroum]

Is there a difference in price?


I dont have anything bad to say about 59mn7a. They had a tendency to come with a badly set gas valve and installers who never check it just left it uncalibrated. But if calibrated properly, the furnace was fine.

I would imagine if there was a major positive difference, it would be trumpeted all over.

If the prices are similar, I would go for 59mn7b.  A little less amperage is always a good thing. You still have lifetime Heat exchanger warranty, so I doubt you should worry there.

I never understood why people correlate the thickness of metal with workmanship quality. The chassis itself is a box. Does it really matter if it's thick, or thin? I doubt it matters in terms of noise, if properly insulated.

I imagine there are goodman level extremes, when you can cut your hand by running it along the ridge of the chassis. But I think Carrier overdoes it with metal thickness anyway.

If there is a price difference. Let's say the dealer is getting rid of its 59mn7As to switch fully to 59mn7B, then go for A.


There is a possibility that Carrier could artificially create differences. Like come up with a thermostat that does your laundry for you, but it needs to communicate with 59mn7B and not A. Sometime, somewhere in the future. That could happen.

[rminoak]

This helps @sergroum.  Thanks.  I'm going to go with the A. 

I have two questions for you @segroum or anyone else... 

and let me know if I should start a new thread but I think these are easy for someone that knows what they are doing.  My existing 92% high efficiency furnace is what is going to be replaced.  My existing combustion and ventilation abs piping runs about 20' each to get to my basement wall with three 45 deg elbows and two 90 deg elbows in each pipe run before going outside.  The 2" abs pipe will be replaced to bring it up to code by the installer.  I calculate my existing total equivalent vent length including the exterior vent length and elbows to be 65'.

1) Is there any issue with the 65' equivalent length using 2" vent or would a 55' equivalent length be that much betteror not?  I have an option of actually going a shorter route that meets all codes that would make it 10' shorter.  I suspect shorter is better but does it really make that much of a difference to abandon old vents and make new holes out the side of the house?  The venting outside is in an dead area that is not used between me and my neighbour anyway where our condensers and utilities for both homes run in.

2) Was thinking of having the installer use the side venting on the new furnace for combustion and ventilation and even putting on a moisture trap or dry well as recommended in the Carrier install manual (manual says for combustion only though).  Is this all overkill or all good practice?  Suggestion?  What would you do?

Installer is recommending using the shorter route to reduce condensation in combustion venting and issue with pressure switch.  This would make the total equivalent length 55' instead of 65'.

[Admin]

You don't have to replace the ABS intake, only the ABS exhaust and 20' is fine.

If they vent out the side of the furnace you don't need a drain tee.  Only if you connect the intake and exhaust to the top of the furnace must this be done.

Download Bulletin TIC2013-0014 here,

https://www.hvactechgroup.com/hvacforum/index.php?topic=1377.msg6196#msg6196

[rminoak]

This is very very helpful.  Helps me be aware of the options and to have a conversation with my installer about it about how mine will be going in.  Thanks again @Admin .