Loving my SLP98
I've had my new Lennox SLP98 now for a month, haven't seen any utility bills yet so can't comment on any savings but this house has never been more comfortable.
Being curious and an HVAC geek, of course I've kept track of firing rates, blower rates etc.
99% of the time, the furnace sits running at 35% and the blower running anywhere from 300 to 370 cfm, the blower rate determined by the discharge air sensor.
Right now it's one of the coldest days we've had and is +6 def F out. This is 11 degrees above design temp. The furnace is firing at 42% and 426 cfm.
After doing a test with digital thermometers that are all calibrated to 1/2 degree or so of each other, all the rooms in the house are within a degree of each other. Temperature swings are 1/2 degree at most. This is a marked improvement from the 5 degree difference there used to be from the end of the house above the furnace and the farthest end away from it.
My old Rheem used to run for 9 minutes and shut off for 22, temps would swing 3 or 4 degrees depending on where in the house you measured.
The Pure Air Media Filter and constant low blower at 300 cmf has dramatically reduced the dust in the house.
Unless the system is recovering from a setback and running above 50% or so it is absolutely silent.
Best feature though, was I received my rebate check from Lennox in the mail yesterday.
Only misgivings are the limited capability of the iComfort Touch thermostat in regards to Dual Fuel and no provision to schedule HP operation to coincide with on-peak/off-peak electric rates.
The outdoor temperature display is extremely inaccurate.
There is nothing that displays whether the furnace or HP is running, or what stage heating/cooling is operating.
The diagnostics display shows several operating conditions, none of which is static pressure.
Other than those limitations the system is awesome and I give it my recommendation!
SJProwler - I too have the XP21/SLP98110 combo but with a HW IAQ tstat instead of the iComfort and have some questions. How long does your furnace run from setback? The furnace is set to the variable capacity mode. I currently have my temps set at 66 sleeping and 68 wake up. I've been tracking my run times and last nite when OT dropped to around 10 F (been very cold here in PA too), the furnace ran non-stop for almost 3 hours at one point during recovery, then it caught up and ran for around 30-35 mins during the on cycles, off for 5-8 mins and then repeats the cycle. During the 30-35 min cycles, it goes from 35% to 53%. Not sure about the firing rate when it ran almost 3 hours as I was asleep then. Per the manual, it shld ramp up from 35% up to 90% during stage 1 call. I'm wondering if it even got up to 90% during the 3 hour run unless the ramp up is really soooo slow as to take 3 hours. Thanks.
My daytime setback is 65 and programmed to restore 70 at 5pm. On a few days that I've been home the system will start recovery about 90 min before but the iComfort is set that it will incrementally raise the set temp by 1 degree at a time. When it begins recovery it raises set temp to 66, when it reaches 66, raises it to 67 etc. However the furnace raises firing rate every 5 minutes that it hasn't satisfied the 2nd stage call. My system is usually running at least 70% or better when it's within 2 degrees of the final set temp.
My thermostat is set for... 1st stage differential 1 deg, 2nd stage 1 deg, 3rd stage .5 deg, 4th stage .5 deg, 5th & 6th .5. Staging timers are set to 20 min, however in heating mode the furnace ignores the staging timers.
I've attached the iComfort thermostat manual, there is a section that explains the staging differentials and timers. It's probably just a matter of setting them up properlly in the IAQ.
Thanks for the update. Unfortunately the IAQ does not have manual differential/timed stage settings. It uses its own proprietary logic which automatically calculates the on/off run times based on CPH setting etc. I've been looking at replacing the IAQ with the iComfort once Lennox works out the problem with not able to do defrost tempering. It just doesn't seem right to me that the furnace will run almost 3 hours non-stop during recovery as it shld be ramping up the firing rate accordingly per the manual. I dont think my system is undersized as its the 110 unit. I'll keep monitoring since this is going to be a very cold weekend here in PA and will definitely be running the furnace.
I know that the iComfort doesn't do defrost tempering but I have yet to be able to tell when the HP is in defrost. The only way I can tell is if I actually catch it in defrost. Mine has never been in defrost for more than a minute or so and the blower drops to a very low speed so you don't feel any cold air from the ducts whatsoever.
I also think that if the DT1 tempering switch is installed on your system between the HP and Furnace W1 leads even with the iComfort it will trigger defrost tempering but haven't checked that yet. The installers had installed the DT1 switch on mine but connected it in error to the board where the Discharge Air Temp sensor connects.
It is now disconnected since I had them install the DAT Sensor for blower control on heating which helped to even out temperatures even more so since the blower is now controlled by the actual discharge temperature instead of a preset speed by the control board.
This is interesting. Does this work for both HP or only furnace? I thought the DAT sensor only works for the EvenHeat strips. So, it will adjust blower speed based on the discharge temp? Hmmm... definitely got my interest... may do the same once I understand more of how this works
Originally Posted by SJProwler
Haven't noticed if it works for the HP but if you look in the iComfort manual in the furnace setup there is a setting for "Fixed CFM" or "Fixed DAT".
I used the default temps under the DAT setup and now at 35% my blower runs at 300 cfm and will go up depending on discharge temp instead of under "Fixed CFM" it always ran at 400 cfm for 35%.
It's -6f outside, no wind, 1 degree below design temp. My sales guy figured my heat loss at 28,500 btu. The SLP98 is running at 38%, 352 cfm blower speed and maintaining the temp at an even 70deg. That's an output of 25,802 btu. I'd say he came pretty close on the heat loss.
The furnace may be oversized at 100% capacity but it's the smallest one available. When it's running at it's lowest capacity of 35% it has pretty long run times.
The day I started this thread it was +6 out but there was a steady 10-15 mph breeze and the furnace was firing at 42% and 426 cfm.
This thing is just awesome but all the credit has to go to the members of this site that shared their knowledge on what to look for in a good contractor, proper installation and correct sizing.
The OAS is extremely sensitive to positioning, e.g., south facing versus north facing. It should not be close to any heat source or direct/reflected sunlight. My installer came to weatherproof the electrical connections and decided to relocate the sensor inside the XC21 cabinet...oops! Temperature readings were accurate during the late afternoon, night and morning...but once the sun warmed the access panel of the XC21, the temperature climbed to 53ºF when it was actually 27ºF. Moved the sensor back outside the cabinet out of the sunlight...problem solved.
Originally Posted by SJProwler
The temp sensor on mine is extremely accurate. It is always within 1 degree of my Davis Professional Weather Station. The Lennox sensor is mounted under my deck and is not impacted by sunlight or wind.
I have no choice on the location of mine, it's under the left grill (looking from the access panel) of the condensing unit. Even at night it's a few degrees off from my Davis Sensor. Odd thing sometimes it's dead on and others it's way off either direction. It's shaded out of the sun. Also I have found that when the heat pump is running it is more accurate.