OK, there's a bit of a disconnect here, but I think we can answer your question. First, the disconnect.
You're saying "temperature," but you're confusing it a bit. You're describing the temperature we feel with our skin, which for the purposes of this question isn't the same thing as the temperature of light. For example, your water is boiling at 212°F, but that temperature is being created (often) by electrical resistance, which is emitting "heat" through power loss. A component of this thermal transfer is photonic, but most of it isn't. Therefore, when you put on some IR goggles you can "see" the hot stove element's IR emission — but you're not seeing something that is 212°F.
There's a difference between "heat" and "light." This is obvious when you consider boiled water and IR goggles. When you convert to degrees Kelvin, water boils at 373°K. But infrared light starts at a color temperature of 4,000°K — and gets colder as you get deeper into the IR range! Here's the sciency part of color temperature:
The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of a color comparable to that of the light source. (source)
Which is a fancy way of saying "heat" and "light" are related, but not the same thing. Therfore, telling us that you're looking for something between 0° and 120°F doesn't make sense. Creatures see color temperature, not "heat." When things create "heat," photons are also created, and that's detectable as a color temperature.
So, let's talk about cones
So, let's completely ignore temperature and look at the wavelength spectrum of light (honestly, it's simpler this way). If you look at a visible color spectrum and draw three lines evenly distributing the spectrum such that 1/6th of the light is to the left of the first line, 1/3rd of the spectrum between the first and second lines, another third between the second and third lines, and the last sixth after that, you'll discover those lines basically center on blue, green, and red.
Your dwarves will enjoy the same basic evolutionary feature.
Let's not use the entire IR spectrum. That's actually really, really wide. Visible light is between 350nm and 700nm. Let's use that width for your dwarves. We'll round a bit for convenience and draw three lines at 760nm, 875nm, and 990nm. Those are the three wavelengths that would correspond to human blue, green, and red.
But does this help?
The funny thing is, unless your dwarves can also see the human-visible spectrum, these three numbers are meaningless to your readers because what they'll see are blue, green, and red. It just won't make sense when they try to describe color to a human.
Color is relative. Nobody sees color in exactly the same way as anybody else. But the absolute differences between wavelengths are not relative. Therefore, using "green" as the center point, the low end is blue and the high end is red. And it doesn't matter if you're talking about human-visible light or your dwarf-visible light.
Which is a very long way of explaining that you're probably barking up the wrong tree. You need to be thinking in terms of language, not temperature or wavelength. What would a dwarf call the "blue" end of their spectrum? Whatever word they use, it won't translate to "blue" in human terms, but it will mean "blue" in dwarf terms.