New Furnace

[Cdn_Cuda]

Well, my furnace decided to pack it in. We’d done some repairs over the years about finally threw in the towel. Couldn’t get new parts for it anyways.

So now I have a mid-level Lennox gas furnace system with two-stage motor. It’s lower BTU than our previous furnace and we’re not sure about it. I’ve got a few questions:

1) They told us it takes an hour to go up a single degree. It was cold the day they installed it, around zero, but it took 8 hours plus to warm up. This seems slow. Is this slow?

2) At no point did the furnace hit the 2nd stage. It stayed low for the entire length of time. I would have thought it would shift into the high speed with such a demand for heat. Shouldn’t the furnace be cycling into the higher level at some point at least?

3) They installed a thermostat and supposedly set it up. I’m going through the options it seems they set it up for a non-high efficient furnace. Would this affect the stage 2 heating? They also failed to program the time correctly and flipped AM to PM.

4) the noise! When the fan is blowing on low it emits I high-pitched noise that I find annoying. Makes me want to pop my ears. Is this normal? My older furnace didn’t make such noises.

Any help on this matter is greatly appreciated!

[Tinman74]

It would help to know the model, just like a paintball gun most modern 2 stage furnace boards have different options for set up. For example some Goodman furnaces don’t need the 2nd stage wire or a 2 stage thermostat to run in both stages. My guess Is you just need your system set up correctly. As for sizing you could use this formula to get you close. Sqft x.7=cfm , cfm x 1.08(specific weight of air)x delta T(70*) = required btu.

[Tinman74]

2000sqft house x.7 would be 1400cfm
1400 x 1.08= 1512
1512 x 70 degrees= 105,840 btu

This calculation will get you close in place of a manual J load calculation

[Tinman74]

Additionally the drive of the furnace fan is important. Every 400 cfm = 1 ton of drive. Basically every 4 supply registers would merit 1 ton of drive

12 registers = 3 tons
16 registers = 4 tons
20 registers = 5 tons

I hope all this helps

[Cdn_Cuda]

Thanks. It’s a Lennox EL296UHV. House is a 1970’s built close to 2,500 sq/ft home. Mostly new vinyl windows, added roof insulation. We’re in the Vancouver, BC, so Pacific Northwest, but fairly moderate temps,

They tried to put in a 60,000 BTU furnace but we refused and they put in a 88,000 BTU. Looking at your calculations we’re still undersized. We have a tech coming tomorrow morning so we’ll see how things go. My dad wanted a 120,000 btu furnace as that is what we had prior.

[Tinman74]

Noise can be many things. If the furnace has too big a drive it can make the duct whistle, a poorly fitted panel, the cover of the filter cabinet not seated all can cause squealing. Hopefully with a brand new furnace it’s not a bad bearing although sadly it can happen.

[Tinman74]

Was the old furnace an 80% efficient furnace (metal flue)
Is the new one a condensing furnace? Plastic flue

120,000 btu furnace @ 80% efficient would be 96,000 btu
100,000 btu furnace @ 96% efficient would have been perfect


The 88,000 will probably be fine the majority of the time however that 2nd stage needs to fire!

[Cdn_Cuda]

Old one was 92 percent condensing furnace.

[Tinman74]

P62,63,64 detail the sequence of operations on a call for heat and how to adjust with the dipswitches

[Tinman74]

FYI: Your unit size code should be 3

[Cdn_Cuda]

Thank you for all the help! Really appreciate it.

[Cdn_Cuda]

Had new techs come by today. Furnace not set up properly. Second stage not active, so furnace only working at half capacity. These guys are fixing it properly.

[Tinman74]

I’m glad it worked out. Did they address the noise issue? The new furnace with ECM motors are generally very Quiet

[Cdn_Cuda]

Seems to have gone away thankfully. Not sure if the bearing needed to break it or what. Just happy it’s gone though!