Backup Power for a Boiler Room and Individual Heating Substation

First, find out whose boiler room it is

In an apartment building, heat supply can take different forms: the OSBB’s (condominium association’s) own rooftop or attached boiler room, an ITP that receives heat carrier from an external network, or a centralized scheme with no substation in the building. The decision on backup is made by whoever owns and operates the equipment. If the ITP belongs to the heat supply company, the question of backup should be discussed with it rather than planned independently.

What exactly needs power

The power of these loads is relatively small, but the running time can be very long, because the heating season does not depend on the length of the outage. Typically backed up: circuit circulation pumps, the controller and regulators, temperature and pressure sensors, motorized valves, safety devices that shut off gas on a fault, and the link to the dispatch system.

What is usually not backed up: high-power electric heating, direct-heating boilers, powerful fans, unless there is a separate calculation. The engineer should be asked about them, because one powerful load can change the whole calculation.

A worked estimate example

Below are hypothetical inputs, needed only to illustrate the methodology’s arithmetic. Suppose there are two circulation pumps of 250 W each running continuously, a controller and sensors totaling 150 W, and a backup of 12 hours is required at a duty factor of 1. Then the total electrical power is 650 W and the energy over the window is 7.8 kWh. With a 20 percent reserve and an inverter efficiency of 0.92, the usable energy reaches about 10.2 kWh, and the nominal capacity, with a depth of discharge of 0.8, a temperature loss of 10 percent and a 20 percent ageing margin, exceeds 17 kWh.

This example shows the main point: the power is small, but the capacity is noticeable because of the long duration. If 24 hours are needed instead of 12, the capacity doubles, so the length of the outage should be discussed frankly. Also check whether the pumps have inrush peaks and whether they are single-phase. The datasheets will tell, not a reference book.

Winter, temperature and batteries

The cold season is when heat is needed most, but it is also when batteries perform worse. Low temperature in the utility room reduces available capacity and, for some chemistries, restricts charging. So the room for batteries should be considered together with the system: whether it is insulated, whether it has ventilation, whether it is shared with the boiler. Recommendations depend on the manufacturer; see the datasheet.

Another winter risk: after circulation stops, water can freeze in pipes on the facade or in unheated rooms. So for buildings with such sections, the circulation pumps and controller should be placed in one of the first priority tiers.

Restoring power: the most vulnerable moment

Not only the outage but also the return of the grid creates risks for the boiler room and ITP. Voltage can return with fluctuations, pumps start simultaneously, and the controller reboots and reverts to factory algorithms. So the question “what happens when the power comes back” is just as important as the question about backup. Ask the maintenance provider to describe the start-up sequence and whether a restart delay is needed to avoid creating a peak. Settings are made by a specialist.

Typical mistakes

• Planning backup without clarifying who owns the unit.
• Trying to back up heating rather than circulation and automation.
• Not accounting for the fact that after an outage the boiler starts under an algorithm that may require stable voltage.
• Placing batteries in a cold room without checking temperature limits.
• Assuming an outage of 4-6 hours, although winter outages can be longer.

What to ask the engineer

Frequently asked questions

Does a gas-fired boiler room need backup power?

Yes, because gas boilers are controlled by electronics and circulation pumps run from the grid. Without power, heat will not reach the building even when gas is supplied.

Can an electric boiler be powered from a backup source?

In theory yes, but an electric boiler’s power is so large that such a system becomes much more expensive. That is why usually only the pumps and controls are backed up, and the engineer decides.

Next steps

Preliminary backup power calculationBattery capacity calculator