How much electricity does a residence need – connection capacity, grid headroom and a transformer station

In brief

A large house with a pool does not need “a bit more electricity”. It needs several times more power than an ordinary house. With a heat pump, a sauna, two car chargers and a heated driveway that adds up to tens of kilowatts, and when everything runs at once, well over 100. Above 40 kilowatts the grid operator treats you as a different category of customer, and the local network does not have to have that power to spare: then you are looking at a network extension or a transformer station, both counted in months. So I ask the operator for connection conditions at the target power before the plot is bought, and I file the application before the plant room is laid out.

How much at once, not how much in total

I will start with a distinction, because without it a conversation about electricity goes nowhere. The meter in the cabinet counts kilowatt-hours, which is how much electricity you used over a month. The grid operator is interested in something else: how much you want to draw at the same time – and that is connection capacity, measured in kilowatts. Water works the same way: the bill tells you how much flowed, but whether the pressure drops with two showers running and the irrigation on depends on the diameter of the pipe. Connection capacity is to electricity what pipe diameter is to water, and that is why it is sized for the worst hour of the year.

In the Polish regulations connection capacity is defined as the highest fifteen-minute average. That detail matters, because it sorts the list of appliances. A car lift that runs for a few dozen seconds barely enters that average. A sauna heater that runs at full power for an hour enters it whole.

An ordinary house asks for a dozen or so kilowatts and usually that is enough, because in an ordinary house the biggest loads are the kitchen and the laundry. The power connection for a house with a pool and a heat pump does not stop at a dozen kilowatts: there are more loads, they are bigger, and some of them run without a break. Let us count.

The sum for a winter evening

For scale I take the house we talk about when we talk about residences: around a thousand square metres of heated floor area, a pool hall, a sauna with a steam room, a garage with a car lift and two chargers, a heated driveway, a large kitchen. And I take the worst day this house will see: a January evening, 15 degrees below zero, snow falling, guests in the house, two cars to charge.

The first item is heating. A new, well-insulated house needs around 40 watts per square metre of the living part at design temperature, so about 40 kilowatts of heat; the pool hall is counted separately. In ordinary conditions a heat pump turns one kilowatt of electricity into 3 or 4 kilowatts of heat. But the colder it gets, the less it delivers – and the more the house wants. At fifteen below, then, an air-source heat pump in many installations calls in its electric backup heaters, which are in essence a very large kettle, and the whole system draws more than 20 kilowatts from the grid. A ground-source unit or a system sized with a large margin looks different, but that has to be calculated, not assumed. The conclusion for our sum is simple: with an air-source heat pump, peak electricity demand lands exactly when it is coldest outside.

The second item is the pool plant. The hall runs around the clock, also at night when nobody swims: most of the energy escapes through evaporation, and drying that air does not get a break. The pumps, fans and dehumidification alone are a few kilowatts, but continuous, all year; heating the water and the hall is a separate line, which the designer calculates together with the heat pump. I write about the pool climate separately, because it is a subject for a whole article – indoor pool climate.

The third is the sauna and the steam room. A sauna heater is sized at roughly one kilowatt per cubic metre of cabin, so a sauna for a few people is a dozen or more kilowatts running at full power for the hour it takes to heat up. The steam generator – around ten. (A sauna and a steam room at the same hour happen less often than their sellers assume, but on a Saturday evening with guests, it happens.)

The fourth is the driveway. Electric de-icing of paving is designed in Polish conditions at around 300 watts per square metre. A driveway of 80 square metres is more than 20 kilowatts – as much as the whole heat pump with its heaters. It switches itself on from a sensor, only when there is precipitation and ice. Which is exactly the evening we are counting.

The fifth is the garage. The most common home charger is 11 kilowatts; two make 22, and if somebody wants to charge faster, twice that. A car lift draws a few to a dozen kilowatts, but for a few dozen seconds, so in the fifteen-minute average it hardly shows. The lift’s power supply, and the day it stops, I cover in the article on the car lift.

Then the kitchen: an induction hob is 7 to 11 kilowatts, an oven another 3. And the rest of the house – lighting, appliances, heat-recovery ventilation, circulation pumps, electronics – a few kilowatts that do not drop to zero.

So that these numbers do not get lost in the paragraphs, the same sum in one table (orders of magnitude, not design parameters):

Added up as “everything at once”, this house comes to more than 100 kilowatts. That does not happen every evening, but it is that evening the capacity is sized for. With the reasonable assumption that not every load runs in the same minute, and that the chargers get what is left, you land in the range of 60 to 80 kilowatts. An ordinary house – a dozen or so. A house heated with gas instead of a heat pump has twenty-odd kilowatts less in this sum, which becomes an argument when the grid is weak.

One reservation. This is an order of magnitude for a conversation about a plot and about connection conditions; it is not a figure for the application. At the plot stage I make this estimate so that I know what to ask the operator. The power balance for the design is calculated later by the electrical designer, on the list of the real appliances in your house. My job is different: to gather that data on time, to file the application before the architect lays out the plant room, and not to let a dozen kilowatts stay in the design out of habit, as if this were an ordinary house.

The 40-kilowatt threshold

There is a threshold of 40 kilowatts in the regulations, and with a residence you need to know it. Up to 40 kilowatts you are an ordinary low-voltage customer for the operator. Above it – still usually on low voltage, but in a separate connection group, with a different procedure. From the sum above it follows that a residence with a pool and a heat pump crosses that threshold practically every time.

What does that change in practice? The application is more serious: besides the site plan and the power figure, you have to state the parameters and the character of what will draw the electricity, because the operator wants to know whether it is heaters, motors or chargers; the network reacts to each differently. The statutory time for issuing the conditions is today a little longer than for an ordinary house: a month instead of three weeks. That is still short. Except that it is the time for a document. The connection itself the operator then builds over a period of several months to more than a year – that is the range the operator serving the south of Poland gives on its own website.

What stands at the plot boundary changes too. At this power the connection cabinet with the metering looks different from the box beside an ordinary house; exactly how, the operator specifies in the conditions. From the cabinet to the distribution board runs my cable, thick and stiff, which cannot be squeezed through a sleeve after the fact. It needs its place in the design, as does the distribution board, which the electrician sizes with spare ways as in any house – I make sure of it, because here that spare means more.

What the street shares: headroom in the grid

Now the thing almost nobody mentions when a plot is being bought: headroom in the grid is shared by the whole neighbourhood.

At the end of the street, or by the woods, stands a transformer station – usually a transformer on a pole, sometimes a small kiosk. Such a station has a transformer rated in tens or hundreds of kilovolt-amperes (in the countryside anything from a few dozen to a few hundred; the small ones around a hundred) and feeds the whole area from it. You can think of it as the distribution board for the entire street: every house takes its share. If we assume, roughly, that a 100-kilovolt-ampere station gives in the order of 100 kilowatts, then the residence from our sum wants as much as that whole station – and no operator will hand the entire reserve of a station to one house. Even if there is still slack there, one house like this uses it up.

Then there is the age of the network. A large part of the rural grid was built in the sixties and seventies, paid for with the electrification fees of the residents themselves, for the demand of those years – and in a Wrocław University of Technology paper on rural substations the power engineers write about the need for its thorough modernisation. Meanwhile the neighbours are adding heat pumps and chargers. The same rule applies to every house: if the capacity has been calculated to the limit, add kilowatts now, because in a few years, when several houses nearby apply for more power for their chargers, the free capacity in that area runs out. Then the operator has the right to refuse or to park the matter until the network is modernised – and the wait is long. Spare capacity in a household tariff is not a subscription: you pay for it once, in the connection fee, not every month (that particular point I check in the operator’s tariff on the day of the decision, because tariffs change). With a residence the whole scale is at stake, so the question about headroom is the first one I ask, before the purchase decision is made.

One more thing: how much headroom your station has cannot be read off any map. Operators publish data on available capacity, but at the level of large substations and for large customers, with the caveat that the data is indicative. The answer for a specific plot and specific kilowatts is one thing only: an application for connection conditions.

Where to check it before you buy

I obtain the connection conditions for utilities before the plot is bought – with an ordinary house that is good practice, with a residence it is a necessity. The application can be filed by the owner, and with the owner’s authorisation – by the future buyer; some operators do not require a proof of title for the application itself, a declaration is enough. The conditions are not yet a contract (for the connection agreement you already need legal title to the plot), but the answer arrives within weeks, and it is the answer that tells you whether the network can take that power without extension, with extension, or needs a new station. How the conditions are transferred to you after the purchase I confirm with the specific operator, because that is their procedure.

What you ask matters. An application for “a single-family house, 15 kilowatts” will get a positive answer in most places and will tell you nothing. The question has to be asked at the target power, with the list of loads, because only then does the operator check whether the station and the line will carry it – and that is what the estimate above is for. The result goes into the same vetting I do for the soil, the water and the zoning plan, described in the article on the plot for a residence.

When there is no room in the grid

Suppose the answer is: there is none. What then? The operator is obliged to connect you if the technical and economic conditions for it exist, and a lack of headroom in today’s network usually opens a conversation about extension. In the typical case the line extension, the transformer replacement or the new station is planned and built by the operator, and you pay a connection fee according to its tariff, which depends on the capacity ordered and on the length and type of the connection. When the operator decides that an extension for a single house has no economic justification, it may refuse – then you receive the reasons and an estimate of what a connection on agreed terms would cost, and on request the method of calculation. With a station, medium voltage and a network rebuild, the cost rules are read in the conditions and in the contract, not in this paragraph. I will not quote figures, because no two networks are the same. One thing I know from practice: you need to know about this money before you buy the plot, because it can change the plot’s price.

The second option: bring the house’s demand down to the power the grid can really give. I do not start by striking out the pool. First I check what can be powered differently, shifted or limited: gas heating instead of a heat pump, if there is gas in the street; a load-management system that measures the draw at the house entry and, at peak hours, throttles what can wait – above all the chargers; interlocks that will not let the sauna and the steam room heat up at the same moment; an energy store that shaves short peaks, though it will not replace the connection. A house designed from the start with such a system can come down from more than 100 kilowatts of “everything at once” to a capacity the operator can give without a new station. Only that decision has to be made before the installation design.

The third option is your own medium-voltage connection. That one has its own section below.

Your own transformer station

At the largest capacities, or where the low-voltage network is too weak, the operator may propose a connection from the medium-voltage line. That means a transformer station on your plot or at its boundary. For a house this is a pole with a transformer, or a small prefabricated building – smaller than a garage, but needing space, an access road and clearance zones. In the design three things have to be solved for it: the place, the noise and the cable route.

First, the place. The station has to stand where the operator’s crew can reach it – at any hour, also when you are away – so rather at the entrance than deep in the garden, and at the distance from the boundary and the buildings that the regulations and the operator set. The regulations say the customer being connected has to make the property available for building the network and provide a place for the metering; what that availability looks like in the land register is read by a lawyer before signing. I also settle at the outset whose station it is to be – the operator’s or yours – where the metering will sit and who is responsible for servicing, because on this depend the costs, the contract and what stays in the land register for years. Second, the noise. A transformer can be audible, especially at night, and it works around the clock. So I do not put a station under a bedroom; on the plan it is easy to miss, and after handover you will not move it. Third, the cable route. From the station to the house runs a cable that needs a route left for it – with no foundations, pool or trees in the way.

And the calendar, which looks different from an ordinary connection. For a medium-voltage connection the statutory time for the conditions is longer, the application comes with an advance payment calculated per kilowatt ordered, and the contract has its own deadlines after which it expires if the build does not start. I will not summarise those rules here, because they changed recently and will change again – that is work for the lawyer who reads the contract before it is signed. My role comes earlier: to make sure the station, the cable and the access to it are on the site plan before the architect places the house so that there is no room left for them.

The calendar: when to file

Everything above comes down to a calendar. The connection conditions arrive within weeks, the connection itself without a network extension within months, and an extension or a station can take many months, sometimes longer than the design of the house. On top of that the conditions have a validity period (since spring 2026 one year from delivery; before that it was two years), within which the connection agreement has to be signed. That is why I file the application for the target power in parallel with the concept work, not after the building permit, but also not too early: conditions that expire before there is anything to sign mean a repeated application, in a network where the free capacity may already be gone.

Site power is a separate matter. A residence takes around two years to build (I describe this in the article on why a residence takes two years) and for all that time the site needs its own supply: the crane, concrete heating in winter, equipment. A temporary site connection is sometimes ready in a few weeks, but I do not put that in the schedule blindly, because with a weak network even site power can get stuck. The rule is the same as with any house: better to arrange the connection too early than too late. A generator with its fuel quickly outruns the standing charge for a connection, and site electricity has its own, higher rates. So I file for the permanent connection and for the site connection in parallel, so that the permanent one is ready before we start installing what will really load it.

Grid headroom and backup power

The two terms sound alike and get mixed up in conversations all the time. Headroom in the grid is the operator’s slack: how much more it can give. Backup power is something else: what happens in your house when the operator gives nothing, because the line is down after a storm. Connection capacity does not solve the second. For that there is a standby generator, which starts with a delay counted in tens of seconds, and a battery backup for what cannot blink: the alarm control panel, communications, the automation. What in the house must work without the grid I describe in the article on the alarm system. The generator is sized for the loads that really have to run during an outage – nobody sizes it for the whole connection capacity.

What I do not promise

I do not promise that the network in the place you like has headroom. Nobody knows that for certain except the operator, and the operator says so only in response to an application. What I can do is make sure that application goes in early, at the real power, and that its result is on the table before the purchase decision or before the first line of the concept.

I will not give you the cost of the connection or of a station before the operator’s answer. No two networks are the same, and anyone who quotes that cost off the top of their head is guessing.

And I am not an electrical designer. The power balance for the application and for the distribution board is calculated by the electrical designer on the list of your house’s appliances; I am responsible for giving them true data and for getting the result into the conditions, the design and the schedule in the right order. There are also plots where, after the operator’s answer, I say that a house with the full electrical programme makes sense only with gas or with its own station – and then you decide whether it is still that plot.

What I ask before I say “it can be done”

These are the questions I start with at every plot meant for a residence with its own technical plant:

1. What target power are we counting – with the full list of loads: heating, pool, sauna and steam room, driveway, chargers, lift, kitchen?
2. Is there gas in the street? It changes the sum by tens of percent.
3. Which operator, where is the nearest station and how far does the low-voltage line run (this can be seen on the base map and on site)?
4. Can the connection conditions at that power be obtained before the purchase, with the owner’s authorisation, and when do we file?
5. What do the conditions say: a connection with no changes to the network, with an extension, or with a new station – and in what time?
6. If a station on the plot: whose, where it will stand, how the operator gets to it, how far from the bedrooms, where the cable runs?
7. How much capacity is left in reserve after everything is added up, and are we designing load management from the start?
8. What has to work when the grid is down? That is what the generator is sized for.
9. When do we file for the site connection, so that the site does not wait for the permanent one?

Questions about the collaboration itself – from the first conversation to the pricing model – I answer in the Questions section.

Frequently asked questions

How much connection capacity does a house with a pool and a heat pump need?

The order of magnitude is tens of kilowatts – in my sum for a large house with a pool hall, a sauna, a heat pump, two chargers and a heated driveway it comes to 60 to 80 kilowatts at a reasonable coincidence of loads, and more than 100 when everything runs at once. An ordinary house asks for a dozen or so. The figure for the application is calculated by the electrical designer on the list of the real appliances.

Can the headroom in the grid be checked before buying a plot?

Yes, but not from a map. The only binding answer is the connection conditions at the target power; the application is filed by the owner, or by the future buyer with the owner’s authorisation, and the answer arrives within weeks. It tells you whether the network can carry that power without extension, with extension, or whether a new station is needed.

How long does it take to connect electricity to a residence?

The conditions – weeks. The connection itself, if the network needs no changes – months. With a network extension or a new transformer station – many months, sometimes longer than the design of the house. That is why I file in parallel with the concept, and the conditions, which are currently valid for a year, have to last until the connection agreement is signed.

Is a transformer station on the plot a problem?

It can be, if it turns up too late – when the house is already placed and the station, the cable and the operator’s access have to fit into what is left. Put on the plan from the start, it can usually be positioned sensibly, but the place, the noise, the access, the cost and the contract terms have to be worked out: whose station it is, who services it, where the metering sits.

If you are thinking about a plot for a residence, or already have one – bring this subject to me before the concept, while electricity can still be asked about rather than rescued. Let’s talk about your project.