Huge temp difference between units

brooklyn215

Hi, new to steam, and have been lurking here for a few months, but I've reached a point where I need some recs

Four unit building, each unit a through floor. Single pipe steam system. Single thermostat located inside apt 1, set to 74F.

Apt 1 only has two 24-section radiators, one with VariValve, the other with a C or D valve.

Apts 2, 3, 4 (mostly) have VariValves, and they have 7 radiators each (~14-section).

Valves in Apt 4 have just been replaced and seem to work well.

On cool days (in the 30-40s), apt 4 rarely gets steam, and the temperature there drops to ~65F. On cold days (20s), Apt 4 radiators get hot and the unit heats up to ~69F.

Apts 2 and 3 see the same pattern, but they get enough steam that their unit temperatures don't drop so much.

The plumbers recommend installing a distributed thermostat that averages the temperatures of all units. I don't understand how is this different to just setting the thermostat to a higher temperature, which would make Apt 1 unbearably hot. My approach would be to replace the valves in apt 1 with smaller ones first and see what happens, but the plumbers say that won't work.

What am I missing? What would you do first?

Jamie Hall

You're not missing anything. Venting is the key to balancing any system with one pipe steam heat.

What you need to do is to take a look around the basement first, and see if there are any main vents on the steam mains. If there aren't, figure out where you might place them.

Now I'm going to be that this building is fairly tall in relation to its footprint. And therefore, to really improve distribution, the risers are as important as the mains in the basement — and you need to take a look at them and see if, and where, you might put main vents on the risers before the radiator connections. This alone will speed steam getting to the upper apartments, and make balancing them much easier. If you can post some pictures of the piping near the tops of the risers, we can suggest ways to do this.

Next thing is to slow down the vents on the radiators in areas which get too hot, or too hot too fast. This is a rather fiddly job, as changing a few vents in one place will affect the heat in other places, so it's something of a try and see what happens and then try again.

Don't worry about changing the thermostat, at least not yet.

mattmia2

I believe those varivalves are very fast even in their slowest setting so they are likely part of your problem. the maid o mist with the set of different size orifices might be a better choice. also harder to tamper with. could also use a few TRVs in a few strategic areas but you have to have it mostly in balance already to use those on 1 pipe steam and you can't use them everywhere, just strategically in areas with largely varying loads.

Long Beach Ed

Assuming that the piping around the boiler is configured correctly, you should be able to get this nearly perfect with the proper venting. Aim to have the system heat each radiator equally.

You'll need some very small vents on the hot rooms to allow the cold ones to get heat.

If you can't get sufficient venting,consider adding a second vent to cold radiators or vents on the top floor of the colder risers.

We also do heat loss calculations of each room to assure that a radiator isn't grossly over- or undersized

A tall building as yours is also affected by solar gain, wind, and NYC whiny tenants, so they'll always be some unhappiness. That's where averaging heat sensors can help.

That's how we do plenty of buildings like yours. You'll save money if you get this right.

brooklyn215

Thank you for all the detailed replies! This is super helpful. I'll try to give these ideas a go, and will post back.

SteamingatMohawk

A fully shut Varivalve vents like a #4. Fully open it's more than a #1.

SteamingatMohawk

If you haven't already looked at it, see this. The table of capacities will help you better understand how your vent capacities compare.

https://www.heatinghelp.com/systems-help-center/balancing-steam-systems-using-a-vent-capacity-chart/