I didn’t. But I see I ended up very unclear. I meant it’s putting out air around 120F because it’s being fed with air that’s around 60-80. If the thermostat was disabled and the input air was warmer than that the output air has the potential to be much higher, barring the internal safety mechanisms which I presumed, probably incorrectly, that the OP would also disable.
I don’t really want to disable the high temp limits but only because I don’t want to damage the heat exchangers and I’m not familiar enough with the physics of it all. Also considering removing the filters or at least installing brand new ones for this adventure.
120 deg return air on something that can make 50 over ambient means the supply air is gonna clock in at 170 deg. I’m assuming the heat exchanger is gonna be a hell of a lot hotter than that but I don’t know by how much or what temperature would cause damage to it. One is brand new the other is fairly old.
I’m considering large Kero or propane heaters but I don’t wanna be overcome by fumes while doing temp and safety checks. I’ve got access to SCBA’s but I’m trying to figure out a way to stick with vented gas fired or electric heat on a budget.
I could pre heat with the furnaces and pipe air in through the windows from portable units. 2150 sft is gonna need a lot of heat. Our 100 deg days are gone but if it’s 85 out side and they’ll get 50 over ambient that should be enough.
It seems that most furnace high limit switches will shut the system down at 170°F to 180°F but there’s some where they don’t cut out until closer to 230°F. So it all depends where in the system it’s located (higher limit closer to the heat exchanger for instance), and there could be multiple ones depending on the sequence of operation, size, and manufacturer. Also, some are limit switches are auto-resetting and others are manual, where you have to push a button. The furnace control board may have lockouts that need to be specifically reset with dip switches, or a simple power down of the system may reset it. It’s hard to say.
It will trip the thermal switch and shut off before taking damage, assuming that it is set up right. And that temperature isn’t going to be that much higher than it’s designed to put out.
And I don’t think it’s damage to the actual heat exchanger that it is designed to protect, but all the other parts of your furnace.
A properly running kerosene heater doesn’t put out much in the way of carbon monoxide. I’d invest in a CO detector anyway. (It’s probably a good idea to have one in any case, sometimes furnaces or water heaters malfunction too.
For the couple minutes every couple of hours you’d be spending in there, it shouldn’t be a problem.
For whatever it’s worth, I see what you did there.
I take the OP a different way, addressing the question of how hot home contents can get without damage.
There’s a general principle that things ought to be able to withstand getting as hot as we can handle them with bare hands. That would be about 60 C.
Also, there are a lot of products people would complain about if they were destroyed by being left on the dashboard in a hot car in the sun, which can be 70 C.
There would be exceptions for things we generally expect to be vulnerable, such as some foods, or medications, or candles. And some things would malfunction, so if you want your home computer equipment to stay on during this experiment, you’d have to check that vulnerability out.
But with a few simple precautions I think 60 or 70 C is safe territory.
Of course, there are some things that are especially vulnerable, such as those foil wrapped “Ice Cube” chocolates, that in my area don’t get distributed during the warm months because they can’t withstand normal handling and storage.
I see what you’re saying. I suppose it’s really two questions. Can I make it hot enough with just the furnaces, and can I do that without breaking my stuff?
My only concern trying this trick would be whether some bugs were hiding in electrical outlet boxes on the exterior walls and whether they got hot enough (and whether they also got into the walls and insulation).
But I guess that’s what the extended time - several hours - is for, to make sure the entire loaf is baked. And… it helps to have the outside nice and hot to start with.
I’d be very careful about a kero heater for this, in other words I would not. They are a very simple design that are not designed to operate at such elevated temperatures. My concern is that the hot fuel and hot air will start ‘super-vaporizing’, and have a run away feedback loop where the combustion rate would be way more then it should and you could have flames coming out of that thing.
All the furnace limit switches I have seen are just simple bi-metal strips with two wires. Auto resetting types close themselves after they cool down. Manual reset is done by pushing a button on the switch itself. It’s designed that way so you actually have to inspect the area to reset it. It’s a snap action bi-metal strip and the button pushes it back over center.
Then there are the catastrophic limit switches for very high plenum temperatures, flue temperatures or flame rollout. They are a fusible link that cannot be reset. You have to buy a new one. And hopefully diagnose and repair the furnace before proceeding.
Plus if this is an 80% efficiency furnace or higher it has a draft inducer fan that pulls the hot plenum gases from the plenum and pushes them out the flue. Those things run hot enough as it is and could easily be a failure point