Old mobile home furnace, refractory liner damage?

rotarydoc

New to the forum, I hope I'm inline with this question for you experts!

The furnace in question is an old Intertherm MAC 1378, mobile home unit, which was originally fitted with gas, and converted decades ago. It's been serving me well for about 40 years now, with the usual stuff, nozzles, pumps, electrodes, etc.

This season started off with a slow start/no start problem, which is kind of secondary at this point, hear me out...

When I took the nozzle/electrode unit out of the firebox, I noticed what looks like (see pictures) serious degradation/damage to the bottom liner (refractory liner?) of the firebox. It has cracks, and a majority of it looks to be missing and/or damaged.

I'm no expert, and info on this is hard to find on the web, at least in my searches...but this seems to be a liner to protect the actual firebox...and if it's missing or damaged, that seems pretty dangerous?

I am wondering (probably) if this furnace is just done, end of life, as the firebox doesn't look very serviceable, it does not have the large, removable front weld plate that I see in a lot of articles or videos...I attached a parts diagram of the closest thing I could find. I did find some info on refractory cement, but this seems like it would be quite difficult to properly prep the bottom of this firebox for application of such a product? And of course, the part is not available, that I can find?

Thanks so much in advance for any info!!

Glenn

HVACNUT

What's the over fire draft readings before and after the fan comes on?
What's the excess air measurement on the combustion report?
Do you have a low level CO detector?

EdTheHeaterMan

As long as there are no missing parts that have fallen in front of the oil burner opening, there should be no problem. I have operated furnaces with cracked chambers that have stayed intact for several years after the cracks appeared. And that combustion chamber is still available If you think it needs to be replaced. But a furnace that old is not really worth it to replace the chamber because there is going to be a real problem getting all the cover bolts off to remove the chamber. It may be time for a replacement furnace.

This would be the chamber https://www.supplyhouse.com/Lynn-Manufacturing-1029-Replacement-Combustion-Chamber-for-Miller-Nordyne-Mobile-Home-CMF-MOC-MGC-901818

You may also need the gasket kit that matches the furnace. https://www.supplyhouse.com/Lynn-Manufacturing-9510-Replacement-Gasket-Kit-for-Miller-Nordyne-Mobile-Home-CMF-MOC-MGC-301205000-660604-688982-689032

STEVEusaPA

40 years for a mobile home furnace? And it's still working? You won!

rotarydoc

HVACNUT,
Thanks for your reply, and suggestions. Unfortunately, I don't have that equipment, or the knowledge to use them. Not an HVAC pro like you guys!

I think I have bad fuel, the reason I say that is someone on the web gave me an idea, so I got a gallon of fresh diesel fuel (what we use here), and took my supply line off, connected a fitting and hose into the fresh fuel, and the furnace fires up instantly. So I either have bad fuel, or a vacuum leak into the pump, which I am leaning against, because when I bleed the pump, the clear bleed hose is perfectly clear of any bubbles. So I still have some research to do on that part. My main concern was the condition of the firebox/combustion chamber before I invest in new fuel, parts, etc. But thanks again for your input!

rotarydoc

Hi EdTheHeaterMan,

Thanks very much for the input, and information. This furnace ran just fine up until the end of last season, so it's probably been that way for awhile, with no problems, as you mentioned. I just felt like it might be dangerous, so I wanted another opinion. Thank you for that!

I have seen those replacement combustion chambers from Lynn, but I am not certain that this combustion chamber is that design. I need to pull the cover off the front and take a look...in other words, if you look at the parts diagram I attached, I don't think my combustion chamber even has a removable front cover/weldplate (or whatever it's called) with all the bolts attaching it. It appears in that diagram like a one piece unit, with a smaller, removable cover with the inspection port right above the burner assembly. Like I said, I need to remove that front cover and take a look to see what I have. I attached the parts diagram, if you can look at it.

I know I need a new furnace soon, just trying to get this one through this winter, if possible. Thank you again for your time and advice, much appreciated!!!

Glenn

rotarydoc

Hey STEVEusaPA,

That is since I have had it...it'll be 50 years old in 2024 (vintage 1974)

EBEBRATT-Ed

@rotarydoc

No contractor would put a new chamber in a furnace that old. It's just too labor intensive to do that with a furnace so close to the end of it's life.

It's probably not worth your time even though it is "free' to attempt replacement yourself.

Just curious if it was originally fired with gas why is it now oil?

If you do get this running it would be wise to check for carbon monoxide just to make sure the heat exchanger is not compromised. 50 years is a very long time for a mobil home furnace.

rotarydoc

Hey EBERATT-Ed,

Thank you for your input and suggestions. I am pretty sure it's time to move on from this furnace, and possibly away from oil altogether, if I replace it. Main reason being that the oil tank out back is also very old, and if it springs a leak, in this mobile home park, I'm in trouble. We do have insurance on the tank, but still, scary thought if it were to start leaking, especially right after a fill.

Your last comment brings a question. I did just recently purchase a consumer grade, typical $50 CO detector, and have put it at or very near the furnace combustion chamber while it's running, and then just close to the furnace in general, and got zero on the indicator. Is this good enough, or should I get one of the more sensitive, commercial type detectors? I have been worried that that damage could cause a CO leak, but so far, it does not appear to have.

I had a big scare with this thing this afternoon, and I see why you guys curse the people that hit the reset button over and over...like I kinda did...

I'm still also trying to figure out why this ignition is so slow to start the furnace...so I had a thought, and I'm lucky I got away with it. I decided to take a look at the electrodes, and nozzle with a video camera that has a very narrow probe (8mm) slipped under the ignition transformer.

Well...it worked, but got really scary. It looked to me like the electrodes are bad, as the spark did not jump the gap, but rather, sparse back on themselves, they are a bit dirty, but maybe have slight cracks, not sure.

Then, the scary part, I had tried to start this thing last night twice, and early this morning twice, and it didn't start any of those times. I figured (ASSUMED!) that that oil had dissipated from the chamber. While I was looking at it with the camera, it now decided it wanted to start,and it did start. I had a huge flame in the firebox, so I ran over and tripped the breaker, but that didn't stop the fire...I had huge flame, and rumbling going on...scared me to death. I lifted the transformer ever so slightly, and pulled the camera out, figuring it was feeding the flame oxygen..

It eventually calmed down, and went out, a good 5-6 minutes later! I've read about huge booms or even explosions, so I guess I got REAL lucky. I did not realize how long a flooded furnace could be dangerous to try to restart again.

At any rate, I think I found the slow ignition start up. I'm going to get a new set of electrodes, and possibly just use this furnace to warm the house a bit and then go over to kerosene heaters and/or electric until I can get a new furnace next season, can't afford it right now.

I do not know why it was converted from gas to oil. It was before I got the home in 1982, so my guess is sometime in the 1970's, possibly due to the 1974/1979 oil embargo, but why switch to oil during those times? Maybe it was the cost of natural gas at the time? I attached a picture of the label.

EdTheHeaterMan

I believe you are wasting your money on any part you put on that thing. every dollar spent on that furnace is a dollar wasted that could go to paying for a new furnace.

Have you looked into the cost of a replacement furnace? Or is burning the house down part of the plan to get a replacement home?

Just asking for a friend in the insurance business.

EBEBRATT-Ed

@rotarydoc

any fuel gas or oil can be dangerous. If the electrodes are cracked or improperly set that can cause delayed ignition as you found out the hard way.

I would be very cautious running that furnace. Try turning on the blower fan and feel around the burner air opening if you feel any air blowing when you start and stop the blower that is a sure sign of a cracked heat exchanger which can also cause ignition problems.

I hate to say this but you are on borrowed time with that furnace.

Using electric heaters is ok if your careful not to overload your electrical circuits. I would be leery of kerosene. Unless it is some kind of sealed heater it will use up oxygen.

What do your neighbors heat with oil? propane? natural gas?

rotarydoc

EBEBRATT-ed,

Thanks for the reply, and information, for sure, I do appreciate it!

Agreed on the electrodes, I think they are contributing to the delayed start, and maybe a bit of old fuel too. I will see how it goes with new ones, set properly. CAREFULLY, this time!

I saw a video with a guy checking a traditional gas furnace for cracks in the heat exchanger tubes, he was using a similar method, with the blower running, but he used a lit match, and watched for any flutter or movement in the flame from a potential crack causing airflow, I was wondering if I could do the same, with a lit match in the combustion chamber, then running the blower?

100% agreed that I am on borrowed, time, it's time for a new furnace, just can't swing it this season, have to work on that new one for next year.

I did go around and replace all the outlets that I will be using for the electric space heaters, with new ones that are heavy duty, 20 amp ones, that have a SUPER tight fit for the plugs, takes a good bit of effort to plug them all the way in. Being an auto mechanic, I have seen, many times what high resistance does to connnections...that, and limiting the outlet to only the heater, and having only one heater on each circuit breaker.

The kerosene heaters work well, but as you say, consume oxygen, so I will be careful with cracking a window or door when those are on, and of course never run them unattended.

I am still a bit stumped by my experiment with the fresh, new diesel fuel. When I ran the furnace off of just that (feeding the pump inlet with a fitting and hose from a fuel container) it fired up immediately, every time. I am thinking that the more volatile fresh fuel would light better, even with compromised electrodes?

My plan, should the electrodes improve the start up significantly, is to only use the furnace, and it's 80 or so gallons left in the tank, to warm the house initially when coming home, and then shut it down. I can keep an eye on it that way, watch the CO detector, and get it warm in here initially, then switch to the electric and/or kerosene, depending on how cold it is. That should get me through this winter in Maryland, it's not too brutal here except for probably some days in January/February.

Most of my neighbors are on either propane or natural gas, by watching the trucks come through. Most have switched off of oil. Myself and a few others in the immediate vicinity are on fuel, but the majority by far are propane or natural gas. I worry also about my very old oil tank and the repercussions of any leakage, even though we have insurance for that, not sure it covers 100% of the clean up if it were to happen..

HVACNUT

@rotarydoc, 20 amp receptacles don't mean diddly if they're on a 15 amp circuit and #14 wire.

The over fire draft test isn't a sure thing to check for a cracked heat exchanger. I mean it is if the fan blows out the flame. But if the flame stays stable, that doesn't rule it out. If you try it, use a BBQ lighter on an angle so your hand is out of the way.

JUGHNE

Mobile home wiring of that vintage may have aluminum "Romex" for all the interior wiring.

This presents another hazard for using electric heaters.

You may have a new outlet at one location that looks to have good connections, however that outlet may be downstream of an older outlet that has questionable connections to maintain good continuity.

This has led to fires in the outlet not in use but is simply a high resistance connection that is overheating.

This is especially true with the aluminum wires.

Been there...done that.

rotarydoc

HVACNUT,

Thanks again for your input, and advice, very much appreciated!

Yeah, I was thinking that the combustion chamber is so much larger than the tubes on that video, that it might not be a valid test. Like you said, if it fails, then for sure I have an issue, but even if I have a smooth flame, it might not...so I'll find out here before too long, when I replace the electrodes, I'll do that test, just to see. I think it's OK, as I get zero on the CO tester, even right up sitting on the top of the furnace, or on the top of any vent I tried while it was running.

About CO testers, I have seen many hand held units that look more "professional" and seem more sensitive than the average (I bought a Kidde unit at Home Depot that has a readout, rather than just the alarm). Do I need something more sensitive in my case?

Thank you again for the input, greatly appreciated!!

Glenn

rotarydoc

JUGHNE,

Thank you very much for your input, and the dangers of aluminum wiring!

Fortunately, this home, even being built in the mid 70's, has copper wiring throughout, every time I have done anything, outlets, breakers in the box, switches, etc, I have always found copper wiring, with a separate ground wire at each outlet, so I'm very lucky in that regard. Still, caution is always better than taking things for granted.

What I DID find, however, long ago, is that whoever wired this home, took the shortcut when installing the outlets, by using the push-in inputs, rather than the screws on the sides...one of the outlets I took out this past weekend, I must have overlooked, because it was still wired that way, and the neutral wire had gotten quite hot, and turned black, and the insulation was hard as rock, and crumbling...I took that wire, cut it back to good, solid wire/insuation, and used the screws on the sides, the proper way. I'm glad I caught that one, all the others I had wired to the screws years ago. Guess I missed that one.

There is a neighborhood nearby here that was built in the same era, real homes, not mobile homes, with aluminum wiring. A few have burned to the ground over the years, and many owners have converted over to copper over the years...scary stuff!

Thanks again!

Glenn

rotarydoc

Update 11/24...I replaced the electrodes in the furnace, and it now fires up INSTANTLY. Wow, what a difference! Just wanted to let you guys know, it turned out well. Planning on using this furnace only when absolutely needed, and then under close supervision with smoke and CO detectors.

Wanted to thank everyone who contributed to my concern, and Happy Holidays to everyone!

Glenn

EBEBRATT-Ed

Backstabbed outlets and switches are no good. Some electricians think they save a lot of time a couple of extra minutes and do it right. Backstabbing always causes call backs at best and fires at the worst.

rotarydoc

Funny you should mention that...as I found another "backstabbed" outlet, another one I must have missed in my not-so-good inspection of these. This one, I found the hard way. Plugged in a laptop charger, and the inrush/sparks immediately blew the breaker...so I thought. Turns out it was not the breaker at all. I had to do some digging/searching on that circuit...what I found scared the hell out of me, and will result in an inspection of EVERY outlet in this home!!! I'm lucky this didn't burn the place down!

EBEBRATT-Ed

WOW that got really hot

JUGHNE

As I learned about the back stab connections over 40 years age, I went one step farther and would connect the circuit wires in the box with wire nuts with a 6" pigtail for the device.

If you look at the jumper between the 2 screws on each outlet you can see that all downstream current must flow thru that tiny piece of brass which BTY is designed to be easily twisted off for half switched outlets.

The twist off piece is already scored/crimped to make the break easier.