Condensing vs old boiler in old building with cast radiators

BigBigEd

I have Slant Fin cast iron boiler, 175k BTU, old but solid in a 5 plex.

Considering NTI as common in Ontario, 150K BTU

Heat loss calc is 100K

In spring and fall, boier kicks in and heats up to the level of the thermostat and kicks off, and the rest of the property gets random amounts of heat.

I'm hoping because a new boiler is modulated, it will maintain water temp and will moderate temps in the apartments.

I have a friend that did just this in a larger building but is having all kinds of problems with temps across his 8 units.

Does a modulating boiler usually mean more consistent heat???

Thanks!

Jamie Hall

No. Consistent heat is a matter of how the system is controlled once the heat leaves the boiler — valves, pumps, piping configurations, thermostats and sensors, the whole thing.

The boiler is just the heat source.

mattmia2

you need to figure out why the heat is uneven. more flow at a lower temp may be the answer in some cases but that is just a solution to a specific problem. if that isn't your problem(s) then it won't help.

mikehvacload

Agree with Jamie and mattmia2 that the boiler alone won't even things out. From your description it sounds like one thermostat is running the whole building, so the boiler shuts off when that one apartment is happy no matter what the other four are doing. A mod con on outdoor reset with the circulator running continuously changes that, because water temperature follows the weather instead of one thermostat, and then thermostatic radiator valves let each unit trim its own rooms. One more thing to check before you buy: if your heat loss really is 100K, a 150K boiler is still oversized, so compare minimum firing rates, since a low minimum is what keeps it from short cycling on mild spring and fall days. Your friend's 8 unit trouble might be worth asking about too, since it could be piping or balancing rather than the boiler.