1 steam boiler, 3 family house, 1st floor has thermostat, gas on house meter. Help.

How do you know how much of your bill was for heat?

I really don’t see any other way of fixing it other than re-piping the boiler to their meter.

And I don’t understand how that can be a reasonable contract when they’re paying for heating the entire building.

Well, it seems to my simple mind that if the first floor tenants control the operation of the gas boiler, they should pay for the gas — one way or another (either in the rent or directly, with the latter preferable). The amount quoted does not seem to me to be out of line, although I'm sure they think so.

However. That leaves the heat from the second and third floor tenants at the mercy of the whims of the first floor tenant — and that could be a problem. In the longer term, I think that what I would at least consider is installing two mini-splits, one for each floor, powered off their respective electric meters, with the interior heads strategically placed. This would allow those two units to control their own temperature more closely —and give you the advantage of advertising that they had a/c in the summer.

Now is this really fair to the first floor tenant? No, it really isn't, since if they run their flat warm,, so that the other two don't need the extra, they are effectively paying for the heat for the other two. One way around that would be that they get a mini-split as well

You would then take the gas bill for the boiler — but keep it as doing the heavy lifting in really cold weather.

If I was paying for the gas, I'd want to be in control of the thermostat

But they don't control it. You made it go back to 68 in 15 minutes, and 64 (at night I guess)

"With shared heat like this, I have split the gas bill based on sqft. In your case might make more sense to split by rad area as the 3rd floor has just a single rad."

As a homeowner I like the idea to ratio the bill based on radiator area, as it's based on simple math that's objectively fair and easily understood by the renters.

2 bed plus den all electric unit with heat pump. Last year January (north edge of zone 5) power use of 760kWh. That includes space heat.

With multi family, each unit is supplying part of the overall heat as each place has only a few exterior walls. Of course with an old leaky uninsulated structure this can add up, but anything code min, the costs are not that high.

Even if each unit has its own gas service/heat, there is typically meter fees that are in the range of $350/year, so not really that much cheaper.

"The lease with the 1st floor tenants specifies that they control and pay for heat."

If you are going to hold your tenant to this lease by making them pay for your houses gas bill then you need to take the setting lock off the thermostat. By your own admission your thermostat settings reverting back after 15 minutes means the tenant is NOT in control of the heat. Be fair to your tenant and charge what you need to charge and you may just have long standing, well mannered, and timely paying tenants. Split the gas meters or change how you charge for heat in the future because this becomes a huge mess when you are essentially making your tenants pay your gas bill too