Grady ? Nordyne M7 - Getting It Dialed In !

First off, sorry for the long read. I am a backstory type of old guy.

Here's my story. Bought this 5k special s/w mobile home along side a woods/stream. Old Miller was in with hx issues. Oil gun had .55 nozzle so I'm figuring 75k btu in 60k out. Anyway the older mobiles had plenty of heat with expected leakage to keep the plumbing warm. Now I house wrapped 3/4 of the skirting except about 10 ft on the south for some air circulation. When I re-plumbed with pex I replaced insulation and repaired the belly with plastic tarp. I added three outdoor thermometers and can monitor the belly temp along with the water meter and temp inside the skirting. I then have the heat tape switchable on the inside and only turn on if needed. The belly stays in the 60's and with it now at 26 out it is 47 under the mobile. A good indication of the heat loss.

As for background, I grew up the son of a master plumber so by my teenage years I was doing plumbing, heating, electrical and carpentry. I worked off and on for my bil's hvac business doing commercial/residential when he was shorthanded. Anyway so I redo my furnace closet and run 2 inch pvc 1-1/2 ft over and 3ft up. I also run 30ft black iron and reduce to 1/2 for the appliances. In the meantime I am dry-walling the hallway and cut the floor out in front of the furnace to put a three inch takeoff for a 2x10 vent across from the furnace to take the chill out of the cold hallway and a 5ft sliding door install in the spring to see the wide life better.

Now to the furnace. I wanted to switch to propane to have back up heat without electric using a 20k blue flame. I was limited on furnaces so I went for the M7 two stage as I got a price from a supplier that was a couple hundred dollars cheaper than Lowe's wanted for the single stage Miller 95. I had previously checked with a m/h guy about 30 miles away who recently installed three of these(2-60k and 1-40k) in mobiles like mine. He said the 40k install people complained they were always cold. So I thought the 60k as I am always on the cold side as I head for the big 70.

Now after all that here's what's up. I had my first stat (old stock HW 8320) didn't want to play well with two stage. I find out after some finagling the stat didn't want to work with the rc and r jumper disconnected. The A/C wiring is wire nutted under the skirting till I need to hook it up in the spring. I'm then thinking hmm I wonder if the stat is defective from new but getting it early and not using it for a few months eliminated my return window. Anyway I just set it for single stage and am using the boards auto staging which seems to satisfy the stat on low setting in the time allotted before it calls high. We keep the stat at 71 since she works part time yet and gets up early and I go bed later. Ok here's what's up. The old furnace I had the blower start at 120 and kick off at 90. When the temps get to teens/singles it hardly had a break before it was off and running. If I remember I had temps at the bathroom register around 120-125 with the blower on high. The last minute or so I was starting to bake and I'd hear the stat satisfy. Ok, on the new one I did some preliminary Delta T's with a dial thermometer in a register downstream 6 ft and a digital thermometer at stat level a couple feet up the hall and got a 57 diff. I'm pretty sure the range is 40-60). I toggled the next higher fan speed and got it to 53. I figure these are the lower speed blower settings. It is definitely quieter that the old Miller. I am surprised as I thought the 58k out compared to the 60k out would be noticeable yet I'm getting the stat satisfied on the first stage. As for temps in the bathroom with the register 6 ft from the furnace I am getting 128. I still get dried at at that last minute or two. My thoughts are dialing the first stage pressure back (4-6), I am set at 5 or bump the fan back. The 2nd stage was 7-9 and we could barely get 8 with the screw just back out a turn. The propane guy says it's set at 11 "wc. I sorta like the lower fan speed but figure I need to get it a little closer to 50 degree mark. Should I do better on Delta T temp locations ? I bought the solid door top return covered it and pull the return through the hollow sidewall which is 3x20 inches with a 12x20 6 merv filter grill with it's top starting at the bottom of the return cut and a 18x20 with a 4 merv spun glass at the bottom to capture some cooler floor air. The top still gets the bulk of return flow. Where do you recommend I take temps ? I can remove a screw and get a reading in the coil box. Would a register temp drop help with that baked feeling. I imagine it wouldn't take much more run time to satisfy the the couple degree drop. I just got a meter to measure w/c so I'd like to check some static pressures also

Thoughts/comments. God bless and have a happy New year.

 

Bump. Are you there Grady

 

There are a lot of threads processed and he is not here all the time.
I'd recommend sending him a PM. Grady private message


I'm having a little trouble following you but I think you're asking about heat rise thru the furnace. That needs to be done by checking the return temperature and the supply air as close as possible to the unit.

 

How I missed this thread I don't know but I guess I did.

I would suggest taking your supply temp in the coil box.
As far as adjusting the gas pressures, the best advice I can give is to follow the installation manual.
The propane guy may have set the regulator gas pressure with no load (they often do) when it should be set under max load.

 

Thanks for getting back. The low calls for 4-6 and the high 7-9 in w/c..I'll have to talk to the propane guy.
What should I be shooting for on the register temps 6 ft away ? Is it odd to have defective HW stats.

 

I believe the stat you had was for a heat pump with electric second stage heat but I wouldn't want to swear to that.

At 6 feet away from the furnace, I would want to shoot for the lower half of the delta T spec.

 

Thanks for getting back. The stat was multi-stage h/c gas, ele. or hp. I'm more at the upper half. I guess the next step will be toggling up the next fan setting. I think i'm at 600 on low fire and 1200 on high before I back off gas pressure I sorta like the quieter blower noise. I rarely hits high as i keep the temp 70 all the time. The timer control seems to be working pretty nice. I do miss having better fan control. The old Miller was temp operated rather than timer. It would keep the hx at 90. On this I have the timer running two minutes after shut down and the hx stays anywhere from 95-109 when the furnace is on a lot. Man I wish I could somehow hack the blower board and have the bower keep the hx at 90 or below or have the fan run on low to circulate every half hour or so. On 95 k furnaces, what is the range of register outlet temps. Thanks.