ᐅ Fireplace and Underfloor Heating – Is Forced Air or Heat Storage More Efficient?

Hello dear forum members,

We have planned a masonry fireplace as a divider between the living room and dining room in our new build.

=> Link to the planning thread
(the planned fireplace extends further into the room, unlike the current layout)

The primary goal is purely aesthetic (fire) and creating a cozy atmosphere. Heating is secondary since we have underfloor heating. Additionally, there is a controlled ventilation system. I am aware of the cost versus benefit issue and that this is purely a luxury feature.

The room where the stove will be installed is approximately 50m² (540 sq ft) with large windows.

I have repeatedly read about overheating problems in rooms when the stove is oversized or when there is simultaneous underfloor heating. Opening a window to compensate doesn’t really make sense.

I have now received two offers from stove builders, but they gave me different advice and would construct the fireplace differently.
Option 1: 12 kW as a convective fireplace (air intake, passing by the stove to be heated, then released back into the room) plus firebrick (refractory brick) storage.
Option 2: 11 kW as a storage fireplace with firebricks, without any convective air circulation.

Both fireplaces seem quite powerful at 11 and 12 kW. I raised the issue of overheating with both providers.
Option 1 says that with the air circulation, the room can heat up quickly when the outside temperature drops and the underfloor heating can’t keep up fast enough. The storage bricks would then release heat after the fire goes out. Without the convective air, the fireplace would be ineffective because it would take too long to warm up. Overheating is not a problem.

Option 2 says the underfloor heating is sufficient to heat the room, so a convective system would heat the room too quickly and cause overheating. The storage fireplace would deliver heat slowly and evenly, helping to prevent overheating. The glass door of the fireplace provides enough heat for short-term needs, so no additional convective air is required.

Now I wonder: who is correct, or which solution is more reasonable?

Thank you for your assessment and help.

If it’s just about appearance, then at most a fan-assisted convection mode and preferably no masonry heat storage.

We had a fireplace with a viewing window and higher output, but also a living/dining area of 75 sq m (807 sq ft). When the fire was lit, the temperature rose slightly (max. +3 degrees Celsius (5°F) in the evening), with most of the heat lost through the chimney. Everything was comfortable.

erazorlll schrieb:

Both fireplaces are very powerful, rated at 11 and 12 kW (37,500 and 41,000 BTU/h), right?

Yes, absolutely!
I’m not familiar with this air circulation system, but I hope you can still take something useful from my post:

erazorlll schrieb:

Option 1 suggests that the air system can heat the room very quickly if the outside temperature drops and the underfloor heating can’t keep up that fast.

I consider that nonsense: underfloor heating doesn’t need to deliver full power all at once and thus struggle to keep up. It runs continuously with an external sensor, so it maintains a comfortable temperature all the time.

erazorlll schrieb:

The storage stones would then release the heat when the fire goes out. Without air circulation, the fireplace wouldn’t help because it takes too long to warm up.

So when exactly do the stones release the heat? Right, when you go to bed. (The underfloor heating is not switched off.)

erazorlll schrieb:

Overheating wouldn’t be a problem.

Overheating means heating a room with too many kW. That almost always happens when you add a fireplace as an extra heat source.

erazorlll schrieb:

Option 2 says that the underfloor heating provides enough heat and adding an air circulation system would heat the room too quickly, causing overheating. The storage fireplace would release heat slowly and evenly, preventing overheating. The glass front of the fireplace would provide enough heat for short-term needs, so no extra air circulation is required.

Even in this case, you have an additional heat source in the room that releases more heat than needed at that moment.
We have 50 m² (540 sq ft) of living space with a large open area leading upstairs. With our 7 kW (24,000 BTU/h) fireplace, we heat basically the whole house, all accessible rooms included. Since the fireplace is used depending on the situation, you generally don’t adjust the underfloor heating much, so when it gets too warm, you just briefly ventilate or go out on the terrace. Your room is also closed off—you’ll be opening all the doors anyway.
What can I say: comfort means warmth, and for overheating, you have to take manual action. Storage stones may be nice, but they store heat for the night, and you don’t need extra warmth then.
Additional technology for a masonry heater is, in my opinion, a waste of money, as is an oversized fireplace.

ypg schrieb:

Thermal storage blocks might be nice, but they store heat for the night, and you don’t really need the extra warmth then.

But there are worse things than leaning against a still cozy warm stove in the living room/kitchen on a chilly morning 😉

KingJulien schrieb:

But there are worse things than leaning against a still warm stove in the cozy living room/kitchen in the morning 😉

Yeah, get ready and go to work....

We chose option two and are very satisfied with it.

One thing is that during the transition seasons, the underfloor heating just can’t keep up. It simply senses that it’s still too warm outside to turn on, and when it finally does, it needs some time to warm everything up. During that time, I, as a woman, was freezing. So I just turned on the stove, and that was enough.

I do find the storage bricks useful because they absorb some of the heat, preventing the room from suddenly reaching 800°C (1472°F).

My father has a standard wood stove in his KfW 55 house, and it’s unbearable when he turns it on.