If I bypassed my thermostats and closed all the doors on a warm day, what is the maximum temperature I could achieve without risking fire or damage to the furnace, window vinyl or home furnishings. I’m sure it depends on furnace type, high temp limit settings, insulation and other things. Just looking for a general idea.
My stab at this one would be what is the coldest it’s been when your heating system could not keep up, or short of that what is the outside temperature when your heating system has to run continuously to maintain the temperature. Both will give you a rough idea of how much temperature difference it can be between outside and inside. Now take that value and instead of a cold winter day, take a hot summer day and add it.
For instance if the outside temperature is -20F and your furnace has to run continuously but can only achieve 68F, instead of the 70F that is set, your heating system can raise the temp of the house 88F above outside temperature.
Now take a 100F day, add 88F and it may be able to get the home to 188F, which seems insane but at least would be a max that would be possible. It however would be less due to the ground and the temperature of the ground. This also would not apply to a heatpump setup.
You may damage the electronics of the furnace if you tried it, but the furnace should be able to get pretty hot. What you might do however is, if you have oil heat, and that oil starts heating before it gets into the furnace it may flow faster and cause more fuel to be passed through the nozzle, thus increasing the BTU (Heat) output of the burner, and be able to raise the home temperature even higher.
My furnaces are natural gas, the only problems I’m seeing so far are maybe the blower motor overheating or tripping the high temp cutoffs.
What do you mean by ‘by-pass’ the furnace? Turn it off?
It’s really an impossible question to answer.
All homes are different. My home that is designed as passive solar, can fluctuate from about 65 degrees to nearly 100. I manage that with windows and a propane stove (used to be wood)
Furnaces generally deliver air heated to around 120F or a bit more if they are properly set up. I’ve measured my registers when I was setting up the flow. Several years ago my son was thinking of buying a Lustron home- a pre-fab all steel house from 1950.
Everything in the house is steel panels - inside and out. Even the cabinets and countertops. The house uses a furnace to recirculate hot air in the ceiling and the radiant ceiling heats the house. The special duct-mounted furnace heated air to 150F. The furnace in this house was missing and they are no available anymore. So he contacted a friend who was an HVAC installer. The friend thought that he could probably tweak a furnace to put out 150F air but it might depend on the individual furnace. He felt that after that the high temp switches would trip. Just an experienced guess but there it is.
I mean bypass the thermostat. Take it off the wall and wire the blower and heat control wires so it’s constantly heating.
I would expect at a certain return air temp that the supply air over temp limits would trip and it would shut itself down. Maybe that would be the max temp achievable without bypassing safeties but I’m not really sure.
How hot does it need to be before a bedbug cooks?
118 minimum for 90min. I figure 140 for about 8 hrs ought to do it.
We recently had a heat pump installed, and it works with our existing gas furnace. We talked with the installers about the temperature of air that comes out at the registers. The gas furnace puts out air around 120° F. The heat pump, less than that. So, I’d say with a gas furnace, you can’t get any hotter than 120° F. Probably slightly less, unless it was hotter than 120°F outside.
OMG, even my 50 year old furnace, that was replaced earlier this year, never ran continuously here in Colorado to the -10’s and the new one runs even less. Maybe someone needs to invest in some insulation.
I’ve read about some companies that put a giant bag over the house and then use industrial heaters to achieve this effect. IIRC it was for a variety of pest infestations. it went on for a few hours or more to be sure all the nooks and crannies and wall interiors got up to temperature. The plastic over-cover ensured that anything in the exterior walls was suitably cooked too. I wonder if it works for cockroaches too?
I’ve lived in places in Canada where it was -40C (whatever that is in Fahrenheit 
) and the furnace kept up just fine - even in older buildings (built around 1960) with 2x4 walls. I don’t know if they sell underpowered furnaces for the southerly states. I agree a more likely issue is whether the heat affects things like the motors, or if the furnace has an overtemperature sensor. (Which would be a logical safety precaution - turn off the furnace if it appears from the temperature inside that the air is not circulating)
It’s -40F, it’s the point where both are the same. On the coldest days we can all come together on the frozen ice pack and celebrate.
It puts out air around 120° F if you feed it with ambient air. If you’re pulling in air from the inside of the house and you remove the thermostat, it would keep getting hotter. Not forever, but I highly doubt 120° F would be the limit for a runaway gas furnace dimensioned to heat a home by itself.
By the laws of physics, no.
By the limits of the safeties in your furnace, you probably won’t get much higher than that.
It will “think” that the filter is clogged, and is not moving air, and will trip itself off.
If the OP wants to get higher temps, get a couple of kerosene heaters as well. Once the furnace has gotten things as hot as it can, get those guys going. Shouldn’t need to worry too much about Carbon Monoxide, as you aren’t really going to want to be in the house yourself.
I assumed the OP would disable any such safeties as well, but I guess that’s not directly derivable from the post itself.
If they want to avoid melting the window vinyl they may have to stay below 160 F. This article is about vinyl siding, which apparently melts if your neighbor’s HE window reflects too much heat on it. https://windowtintz.com/vinyl-siding-melting-point/
I see what you did there.
That’s not how it works. 120°F is the supply air temperature with a return air temperature of around 70°F which is a 50°F delta. Since a gas furnace is literally fire in a box, there’s no reason to think it couldn’t heat 150°F air to 200°F which is also a 50°F delta. Of course then you start running into the over-limit protections, failing fan motors, wires, or even the limit of the heat exchanger itself. To make air that hot, the heat exchanger is already much hotter, so as the temperature rises it could break or even melt.
As soon as I saw the thread title I was thinking “oh no, bedbugs.” It does seem like it should be easier to just blast the furnace in the heat of summer rather than getting a company to tent the place and do it with propane heaters or whatever. The thing is, unless you could heat up the house so much inside that the walls were hot to the touch outside, then I don’t think it would do the job. Even a poorly insulated home would need to be ridiculously hot for the exterior siding/brick to reach 120°F in the shade.
Then there’s the fact that hot air rises, and with the house so hot, it exacerbates the chimney effect. That means the basement or crawl space, which is already the hardest part to heat, is also trying to suck in air from the outside to replace all the hot air that’s forcing its way out of the attic. A tent mitigates this, by keeping all the hot air in a bubble, rather than letting it bleed out into the environment.
Why do you think it would be pulling in outside air?
Anyway, from what I’m reading elsewhere, it sounds like a) there are safety limits inside the furnace governing not just outgoing air but also incoming supply air. You won’t be able to do what you are wanting. Also, if you did, it would likely damage the furnace and therefore cost more than just paying professionals to do it.
Overriding the thermostat is easy.
Overriding the temperature switch built into the furnace electronics is going to be a bit more involved, and certainly void your warranty.
And that switch isn’t there just to keep you from getting your home to a comfy easy bake oven temperature, it’s there to protect the furnace itself.
That’s how I got rid of bedbugs when I had an infestation some years ago. The outside temp was just a touch over 100 that day. I had a manual thermostat, so I just had to peg it all the way up. Then I put a couple kerosene heaters in the basement. I disconnected the dryer vent and turned that on as well. About half way through the day, I went in and change clothes to the clothes that had been in the dryer, and turned it on again, just to make sure that I didn’t have any hanger’s on.
I pulled out couch cushions, and moved beds and mattresses around to be out in the open and standing. I removed shades from windows, especially the ones that get the most sun. Those rooms are usually 10 or so degrees warmer when the sun shines in. I turned off and unplugged all the electronics.
Had a bunch of thermometers throughout parts of the house, and fans to distribute the heat and to blow on walls and furniture. Went in every hour or so to check on things, and by noon, the lowest temp reading was 121, some were pushing 130.
Just for shits and giggles, I had bought some bed bug fumigation cartridges, and set them off at this time.
Kept it up until around 7pm, when the temp outside started to go down, moved the fans to the windows for a couple hours before I bothered to turn on the AC. I did note that I had forgotten about the soap on the bathroom counter. That had melted into a nasty mess.
Haven’t had a problem with them since. I keep a couple of bed bug traps in a few locations through the house and near my bed. They don’t do anything to stop an infestation, but they let you know if you have one.
Did you do anything with your refrigerator/freezer? That might go off on thermal overload but perhaps not.
No. I wasn’t sure how well they would work, but they held up just fine.