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Lennox G51MP Furnace

1.2 of 5 stars 5 reviews | #24 of 26 Furnaces
Updated: Feb 15, 2019 | Read more about Lennox Furnaces | G51MP Warranty

Overview of G51MP

The now-discontinued Lennox G51MP gas furnace is considered a high-efficiency unit, with input capacities ranging from 44,000 to 132,000 BTU/H and cooling applications from 2 to 5 tons. As either a direct vent or non-direct vent gas furnace, this multi-position unit can be installed in various locations throughout the home. The removable heat exchanger, burners and manifold assembly allow for easy access during maintenance. While it is a natural gas furnace, LP conversion kits are available.

The G51MP furnace is equipped with a "clamshell-type" Duralok Plus heat exchanger made of aluminized and stainless steel. Lennox uses its silicon nitride SureLight hot surface ignition in the G51MP; this feature gives the furnace the capability to adjust the amount of energy used at start-up so no more is used than necessary, thereby increasing the starter's longevity. In addition, redundant gas valves are used as a safety feature that shut off the unit if necessary.

Furnace Filters for the Lennox G51MP

Air Flow Configuration Cabinet Width Filters
All 17-1/2" 1 16x25x1 filter
(side air return)
All 21" 1 20x25x1 filter
(bottom air return)
All 24-1/2" 1 24x25x1 filter
(bottom air return)
All All 1 16x25x1 filter
(side air return)

Consumer Reviews of the G51MP

1.2 1.2 of 5 stars 5 reviews
  • Very Satisfied
  • Somewhat Satisfied
  • Neutral
  • Somewhat Unsatisfied
  • Very Unsatisfied
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1 of 5 stars Dryden, Ontario
Date created: 2019-02-15

Forget the warranty

Undependable. The furnace has quit many times. Parts are expensive and also unreliable. The dealer would give no warranty and neither will Lennox. Buyer beware!!!

1 of 5 stars Northern Ontario
Date created: 2019-01-27


We live in Northern Canada where temps often go to -40. For this reason I wanted the best most dependable furnace I could buy...this wasn't it!!! It has failed many times. Supposed to have a 10-year warranty and I have volunteered to send failed parts back to Lennox, which include failed venter motor ($412) and two thermostats, as local installer and repairmen want nothing to do with warranty. Neither does Lennox. We never leave the house overnight without shutting the water off as furnace may quit and pipes may burst.

2 of 5 stars Washington
Date created: 2016-12-17

Suspect flame sensor

Bought and had installed in Nov. 2003 for approximately 31000. About every other year the flame sensor needed to be replaced. It is in a bad location and once it was cracked and had to be replaced, how did it crack? Needs to be cleaned often or will not cycle on and you have to turn the unit off for a while and hope it functions properly after that. Here is the total amount spend to date just on flame sensor repairs as of Dec.15, 2016: $661.22. It is malfunctioning again and I believe I will get an air spray can and clean it myself, might be time to get rid of it. My old Coleman gas furnace was removed (still worked but very costly) and no credit was giving for it, should be glad I didn't have to pay for removal, LOL.

1 of 5 stars Winnipeg Manitoba
Date created: 2015-03-04

Getting the runaround getting parts

I have a Lennox furnace that quit working. I need the Surelight circuit board so I Googled Lennox and got Lennox PartsPlus. I phoned and got a guy that told me to phone another number so I phoned that one. The girl on the phone tells me I need to be a dealer. She refers me to a local dealer that tells me they do not sell to the public. She can send a service tech out, so I will have a $1000 bill by the time the tech leaves. I ordered one on line for $150 and can replace it myself. Instead of supporting the local business, I had less grief going online.

1 of 5 stars Lafayette Ind.
Date created: 2011-02-04

Cost Effective

Very cost effective furnace, mainly because it does not work. Installed 6-06, starting in 10-09 it would just quit no reason and has continued this until now 16 months. 33 services calls to company they are baffled no charge to me. Time for an attorney or new furnace. Biggest pos I have ever seen. Lennox G51MP

Other G51MP Reviews

In many online discussion boards, homeowners complain about this furnace's failure to turn on or provide hot air. According to a homeowner writing about this problem on, one reason is that the G51's pressure switches seem to fail regularly. However, in many of these situations, cleaning out the condensate trap seems to solve the problem. Grounding issues also seem to be common for this furnace.

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Lennox G51MP Model Numbers

The G51MP is available in different models which vary in efficiency and capacity.

Model Number AFUE BTUs per Hour
G51MP-24B-045 92.1 44,000
G51MP-24B-045-** 92.1 44,000
G51MP-36B-045 92.1 44,000
G51MP-36B-045-** 92.1 44,000
G51MP-36B-070 92.1 66,000
G51MP-36B-070-** 92.1 66,000
G51MP-36C-090 92.1 88,000
G51MP-36C-090-** 92.1 88,000
G51MP-48C-090 92.1 88,000
G51MP-48C-090-** 92.1 88,000
G51MP-48C-110 92.1 110,000
G51MP-48C-110-** 92.1 110,000
G51MP-60C-090 92.1 88,000
G51MP-60C-090-** 92.1 88,000
G51MP-60C-110 92.1 110,000
G51MP-60C-110-** 92.1 110,000
G51MP-60D-135 92.1 132,000
G51MP-60D-135-** 92.1 132,000

G51MP Warranty

The G51MP furnace carries a 10-year warranty on parts and labor. It is important to discuss your warranty in detail with a Lennox dealer.

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