In the house I just bought I have a fireplace in the living room. I'm not a fan of fireplaces, but cost of total removal is too high so I bought few plasterboards and will simply cover entire chimney breast, plaster, and hang a TV on it. About the chimney itself, I heard two conflicting theories. One being that if I block it off with something like chimney balloon, it will help the room retain heat which it currently is losing very very fast. Another theory I heard is that you cannot do it, and that after I put my plasterboards around it, I should make a small vent at the bottom to let chimney breathe. Which one is correct? I would personally prefer to completely close it off and improve room's thermal efficiency, but at the same time I don't want to do something that may cause me issues in few years time...
Vent it either side or front. Ever time imo having had problems myself. Need air to blow through more in winter than summer. If you cap the top your less likely to get water or damp if you block off but vent is way to go to keep air flow
Alright then, I will buy something like this and mount it at the front bottom of the fireplace, hopefully that will be enough. https://www.screwfix.com/p/map-vent-fixed-louvre-vent-with-flyscreen-brown-229-x-152mm/570hy
By allowing your chimney to breathe, all you're doing is pouring your financially and environmentally expensive heat straight out of your living room and into the skies above your house. Not great! Just because a chimney was designed to breathe doesn't mean it has to breathe, and I have blocked off all of my unused chimneys without any issues. If you insist on letting it breathe then let it breathe using outside (unheated) air only. Make a hole from the outside into the base of the chimney which allows air in from the outside to pass up through the chimney to escape at the top of the chimney. If the top of the chimney doesn't have a rain hood, then fit one to reduce the amount of rain that can fall down the chimney, which would then require drying. If it already has a hood, then all's well. Your chimney can breathe to its hearth's content without the need for wasting heat.
I was thinking about your comment since yesterday. My house is a semi and chimney is in the middle, so I can't drill it from the other side. So what you are saying is that as long as I put some sort of rain/anti bird cap on the top, I can block off the chimney in the living room without any long-term consequences?
I would seal it at the top ... not just cap it with a rain hood, as that would still allow an air exchange and could result in some condensation inside the chimney. The fact that it's entirely internal to the heated house means that there is no risk of condensation collecting on the inside surfaces, so as long as there is no airflow that brings new potentially damp air. If no new air can get it, the air trapped inside will eventually dry out and no damp can occur
Alright, thanks for help. I guess that's the plan. I will buy this C-Cap and install it soon. One last question, what would you block the chimney off with at the fireplace level? When I moved into this house, I found a pillow in a plastic bin bag stuffed into the fireplace. Not sure if that's a good idea, but since I am building a wall around the fireplace, I need something that I can safely put in there permanently. Edit: Actually, since I will be putting a c-cap that will seal the chimney, does it even make sense to block the fireplace off with pillow/balloon/whatever?
Just stuff some rockwool up there to slow down whatever convection currents there may be as a result of temperature differences.
Make sure its swept too as you don't want the odd fall of soot or loose mortar ending up against the bottom of your new wall blocking off the fireplace although as said above stuffing rockwall up will mitigate that anyway
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