Choosing the Right Buderus Condensing Furnace Power for a 118m2 House with Underfloor Heating

Hello,

I am asking for advice on selecting the power of a condensing furnace. I had 24kW in the project, but recently I was offered a 14.9kW furnace.

Newly built house of 118m2.
The stove is to be in the bathroom with a tray (separate). The sink in the kitchen is about 2.5 meters from the stove. Above the bathroom is the upstairs bathroom.
The house has 1 bath, 1 shower, 2 toilets, 2 sinks, 1 sink, 40cm dishwasher.
Additionally, there will be a free-standing stove in the living room.

Ground floor: underfloor heating + towel rail radiator in the bathroom
floor: radiators in 3 bedrooms, small hall, ladder in the bathroom, but underfloor heating in the bathroom.

Buddy, I personally recommend Dietrich. Affordable and of very good quality.

Only about what power? 24kW or less?

Buddy, power And you will also limit it programmatically. In your case, 18kW should be OK.

Thank you for your answer.

daro31ie wrote:

Buddy, power And you will also limit it programmatically. In your case, 18kW should be OK.

Why 18kW exactly, how do you know it?

Friend? Bajarka79 why floor heating mixed with radiators in a newly built house (I do not mean ladders in the bathrooms)

daro31ie wrote:

Buddy, power And you will also limit it programmatically. In your case, 18kW should be OK.

For heating purposes, it is the minimum power that matters, not the maximum power.
Supposedly, the standard for single-family houses from 2017 is 95kWh / m2 per year.
95 * 118 = 11210kWh per year for the whole thing, so I will go for heating from this, I shoot about 70%, which is approx. 7850 kWh.
With so little energy demand, the minimum power is very important.
Although here it is a floor heating + radiators, may it not work out for the investor, if he has problems with tuning the whole.
I am not a professional, but I can barely see the heating of radiators when the floor heating is already warming up, without an appropriate heat buffer it can be poor.
It is worth asking and asking specialists for advice before buying and installing.

kasprzyk wrote:

daro31ie wrote:

Buddy, power And you will also limit it programmatically. In your case, 18kW should be OK.

Why 18kW exactly, how do you know it?

Friend? Bajarka79 why floor heating mixed with radiators in a newly built house (I do not mean ladders in the bathrooms)

That's what you advised me from the installation. It was about the comfort of sleeping in the bedrooms, because apparently the air is bad at the floor. I also know this from people who only have a floor.

It is known that a mixer will be installed.

If the same gentleman advised you a 14.9kW boiler, I suggest you change the installer as soon as possible and use the feed mixer.
Ask this "specialist" how the air circulates at a high-temperature radiator and, as with a low-parametric floor heating, ask him also when the efficiency of the condensing boiler is the highest, unless you do not care about the economic operation of the entire system.
If you do not have a bare brick house built, let your pseudo installer choose the boiler power in terms of the possibility of preparing DHW and not the maximum CH

kasprzyk wrote:

If the same gentleman advised you a 14.9kW boiler, I suggest you change the installer as soon as possible [...]
If you do not have a bare brick house built, let your pseudo installer choose the boiler power in terms of the possibility of preparing DHW and not the maximum CH

Only in my opinion, such posts do not help the author, because they do not explain anything.
Although I have licked the subject of heating myself, I do not see a problem in heating a domestic hot water tank with a capacity of e.g. 150 l with a gas boiler with a power in the range of 1.9-12kW, since electric boilers usually have about 2kW.
I am aware that the planned consumption of domestic hot water will affect the selection of a tank with an appropriate capacity and a boiler with appropriate power, so that the time of preparing domestic hot water will not be too long.
But I cannot make calculations myself to match everything correctly and choose the most optimal option, but I do not understand why you disqualify the installer who proposed the 14.9kW model in advance.

When choosing a gas boiler, we will always face the dilemma of what to choose:
- low minimum boiler power of e.g. 1.9kW for central heating needs, at the expense of lower maximum power for domestic hot water,
- higher maximum power of the boiler for domestic hot water needs, at the expense of higher minimum power for the needs of central heating, exceeding the actual heat demand
I have doubts which solution will be definitely better, because I have not had any practical contact with any of these solutions in a building insulated according to the latest standards with underfloor and radiator heating.

Bajarka79 wrote:

It is known that a mixer will be installed.

Just remember that if you have an underfloor heating system downstairs and radiators on the top, then this "mixer" is preferably a separate heating circuit on the mixing valve and an actuator controlled by the boiler automation with a separate heating curve for radiators and a separate heating system, and the best remote control with readout temperature at the top separately and at the bottom separately. Do not be persuaded to buy a floor heating manifold with a built-in thermostatic pumping and mixing system, because then there will only be questions about how to set it right, because it's either too hot or too cold.

Thanks for the answers. Now I know at least what to ask and what else to pay attention to before buying and installing.

Added after 24 [minutes]:

Would someone be tempted to give a specific proposal of a condensing furnace with all the accessories to my home?
Information about the house is in an earlier post.
The house will be insulated with 20 cm polystyrene.
BATHROOMS are one above the other and the sink is about 2 meters from the stove. The rest is unchanged.
Maybe there are more heaters on the floor?

Added after 1 [minutes]:

One more thing: could it do without a separate water reserve?

BUCKS wrote:

Only in my opinion, such posts do not help the author, because they do not explain anything.

Pay attention to the nature of the questions asked, the person is asking as a layman, and in a moment he uses the phrase " you know that a mixer will be installed "
So let the questioner determine whether she is interested in possible correct solutions, whether she has an installer, brother-in-law / uncle Kazio who, as a handyman, has a plan and waits only for the approval of others, and considers any words of criticism to be an attack on his wonderful plans.

Coming back to the essence of col. Bajarka79, please read a little here about the selection of the tray: https://www.budkuje.pl/wiadomosc/zasobnik-cwu-jak-wybrac-jaki-najlepszy/1192/ (the first result found in google, you can look for this more) if it is decided on the size of the heater, you can select the heating boiler.
I would not worry about the power reserve for CO here - only very important - with a condensing boiler, floor heating throughout the apartment - what advantages? please read e.g. here: http://www.e-instalacje.pl/a/podlogowka-zalety-i-wady-3932.html
If you have a lot of money - please make a mixed installation - floor heating and radiators everywhere (I have met one of them), the client explained by the fact that it is possible to regulate the daily temperature in the rooms - in practice, the cooling of currently well-insulated flats is so slow that such regulation is not right being. If someone is too warm in the bedroom - it permanently reduces the daily temperature.
Condensing boiler, heat pump - only underfloor heating !!! Mixed installations - throwing money down the drain, additional costs of separate heating circuits, uneconomic boiler operation, cluttering the apartment with radiators, please think carefully, and stories about bad air are just nonsense, myths of grandma and grandparents who once refused to use plaster walls, because they are smooth and don't "breathe"