Idea: Use chimney as a duct?

[ThomasN]

Hello!

We have a functional house from 1938. It was previously heated by an oil burner in the basement, but now we use district heating. There was also a fireplace in the "recreation room" in the basement, which we plan to remove.

The chimney is now almost unused, with only a little ventilation going through it. We may want to have a fireplace/stove on the ground floor in the future, which should be taken into account.

My idea was to use the large area that the chimney has to run water and electricity (we are going to completely renovate the house). The chimney is in the middle of the house, so it should be smart to start from there. It's also good in the basement since both the district heating exchanger and the electrical panel are very close to the chimney.

We plan to redo all the electricity and water from scratch.

What do you think, is this a good idea? Are there any regulations that might get in the way if we want to keep the option open to use a channel in the chimney for a future stove on the ground floor?

Offhand, I think that if you just insulate well, it should be OK? Of course, you would need some kind of liner for the chimney pipe for the future stove.

 

[ThomasN]

Made an example of how it might look. The distribution should not be just like that, but the main idea is conveyed (hopefully)...

 

[Tornhill 2]

Hello Thomas,

With outer dimensions of 700x1200, you probably have eight, or more likely, six flues in the chimney. Each flue probably measures around 12x12cm, maybe one measuring 12x24. Climb up on the roof and look down the chimney, then you'll see how it looks.

One has previously been for the oil burner and one for the fireplace in the den. One might be used for the kitchen fan?

Then there's the ventilation. In a house from '38, it's natural draft unless someone has changed it later. This means that warm air from inside the house rises through the chimney, so that new air is drawn in through, ideally, ventilation openings, and in the worst case, through various windows and leaks.

I think the first thing you should do is thoroughly check the chimney. How many flues are there? Where do they start? It's quite possible that several flues have been sealed off/collapsed after repairs/renovations long ago. Ideally, you should have a ventilation flue from each room, especially from bedrooms, if you intend to continue ventilating with natural draft. I would want a ventilation flue for every bedroom adjacent to the chimney stack. Fresh air vents in the walls are to bring in fresh air, not to expel stale air. From the basement, I would also want at least one ventilation flue to avoid moisture problems.

So, future fireplace, one flue. Kitchen fan, one flue. Two bedrooms (for example), two flues. Basement, one. Living room, one (if the future fireplace is in the living room, you can skip this one). That makes five to six. Then you might have zero to three left over. These could be used for water and electricity, especially if you have the flue for the fireplace next to the kitchen fan, both with liner pipes and insulation outside the pipe. Then you have the flues for ventilation, and at the far end, you have water and electricity.

To be sure, I think you should call the chimney sweep. He's the one who should approve the smoke flue if you ever connect a fireplace.

/ Fredrik

 

[pinebar]

I don't think there is any advantage in doing so. Nothing becomes easier or better than making new shafts. How, for example, will you attach the water pipes inside the chimney? I think it is easier to make another hole in the floor near the chimney and build the items into their own shaft next to the chimney. All joints on water pipes must be possible to inspect. Regarding water, you also want to insulate so that hot and cold don't mix unnecessarily.

We also have a 1930s house and considered laying a main line for electricity and ventilation next to the chimney. But due to partitions in the flooring and an open plan on the ground floor, we chose to make a couple of shafts in other places instead.

In our chimney, there are four ventilation channels and one for burning. We will continue to use the ventilation channels for ventilation.

 

[ThomasN]

Hi Thomas.

One was previously used for the oil furnace and one for the fireplace in the rec room.
One might be used for the kitchen fan?

Then there's the ventilation. In a house from -38, it is natural draft unless someone has changed it later on. This means that warm air from inside the house rises up through the chimney, so that new air is drawn in through, ideally, ventilation openings, or, in the worst case, through various windows and gaps.

I think the first thing you should do is thoroughly check the chimney. How many channels are there? Where do they start? It's quite possible that several channels are bricked up/collapsed after repairs/renovations long ago.
Ideally, you should have a ventilation channel from each room, especially from the bedrooms, if you want to continue ventilating with natural draft. I would like to have a ventilation channel to all bedrooms adjacent to the chimney. Fresh air vents in the walls are for bringing in fresh air, not for expelling old air. From the basement, I would also like at least one ventilation channel, to avoid moisture issues.

So, future fireplace, one channel. Kitchen fan, one channel. Two bedrooms (for example), two channels. Basement one. Living room, one (if the future fireplace is in the living room, then you can skip this). That makes five to six. Then you might have zero to three left. You should be able to use those for water and electricity, especially if you have the channel to the fireplace next to the kitchen fan, both with inserts and insulation outside the pipe. Then you have the channels for ventilation, and the furthest away you have water and electricity.

To be sure, I think you should call the chimney sweep. He is the one who needs to approve the smoke channel if you ever connect a fireplace.

/ Fredrik

The kitchen fan does not go via the chimney but goes the nearest way from the kitchen out through a vent in a wall. However, I am considering that when we renovate the kitchen to change so that I have the fan on the roof instead to keep it quiet in the kitchen.

Indeed, it is natural draft. Almost all vents are sealed with insulation and covered with fabric/wallpaper. But no problem, the very drafty windows currently provide more than enough fresh air, it seems This will soon change when we add extra insulation to the facade and replace all doors and windows.

Is the chimney really functioning well now that we're not burning anymore? If we opened up the ventilation channels, I don't see why the air would "prefer" to rise out through the ventilation channel in the chimney rather than out through the vent. That is, why the airflow would go in through the wall vent and out through the vent towards the chimney.

When I was home having lunch today, I stood pondering this a bit. Maybe I should tear down the entire chimney and build a new one, more efficiently distributed. Then I can prepare for an insert pipe for a stove that is significantly separated from the rest, ventilation pipes to all rooms that should be "connected" (if that's the best way to handle ventilation, that is), water & electricity. Then I can also build an inspection hatch so I can easily access the chimney on each floor, both for easy installation and for future operations.

I called a chimney sweep this morning and discussed a bit. We might book a time for next week to go through it.

 

[ThomasN]

I don't think there is any advantage to doing so. Nothing becomes simpler or better than creating new shafts. How are you going to attach the water pipes inside the chimney? I think it's easier to make another hole in the joists near the chimney and build the items into their own shaft next to the chimney. All joints on water pipes must be possible to inspect. When it comes to water, you also want to insulate so that hot and cold do not mix unnecessarily.

We also have a 1930s house and considered placing a main stack for electricity and ventilation next to the chimney. But due to dividers in the joists and an open floor plan on the ground floor, we chose to make a couple of shafts in other places instead.

Our chimney has four ventilation channels and one for burning. We will continue to use the ventilation channels for ventilation.

To secure everything, I was planning to make holes in the chimney on each floor. Maybe, as I wrote in the above post, I will redo everything from scratch, then that point will be resolved.

I think it seems perfect to have the chimney as a starting point since all the rooms more or less adjoin the chimney.

I wonder if the chimney has a load-bearing function... if it doesn't, it's not super difficult to tear it down and start from scratch.

 

[Tornhill 2]

In a house from 1938, my guess is that the chimney does not have any load-bearing function. In older houses, it very well might have.

The advantage of ventilation via the chimney is that you only need one vent in each room, specifically for supply air.
If you solve it with just vents, you need one, placed high, for exhaust air and one, placed low, for supply air. Alternatively, you need to start looking at solutions with forced ventilation, i.e., various fan (system) solutions.

Then you are right, the ventilation via the chimney works much worse now that you no longer have an oil boiler in the basement that heats up the chimney.
At this time of year, it works well anyway, the indoor air is typically 20o C, and the outdoor air is 10o. Warm air rises... But on a hot summer day, when you were still using the oil boiler for hot water, it can be 30o outside. Then the natural draft stops working

/ Fredrik

 

[Tornhill 2]

Then you have the problem that chimney flues are quite narrow. It can be tricky to insert/remove/attach/join electrical and water pipes in them. On the other hand, you have a good solution for water leaks, everything drains down to the basement, where hopefully you have a floor drain that takes care of the mess.

/ Fredrik

 

[pinebar]

But on a hot summer day, when you had already fired up the oil burner for hot water, it can be 30 degrees outside. Then the natural draft stops working

/ Fredrik

But it doesn't matter, because then you just open the windows.

 

[norrbottenstorpet]

Aside from any potential issues you may have with possibly needing channels for proper ventilation, there is at least one other issue: the installation of electrical cabling in a space where you can expect elevated temperatures (if you add a future fireplace). The regulations and sizing normally assume non-elevated temperatures, which may require different sizing or, in the worst case, different material.

I would not choose to install electricity in a chimney stack if part of it might be used as a flue.

I would also consider an FTX ventilation system (supply and exhaust air with heat exchange) if the plan is a total renovation of a house, even if it previously worked with natural draft, especially when the heat source that "drove" the natural draft is gone.

 

[ThomasN]

Maybe like this:

The chimney is demolished except for a U consisting of a short side and what I now need to keep on the long sides to have enough width for the liner. Build a new short side against the small remainder of the long sides. What remains is now a chimney of maybe 700x400 (from 700x1200).

Next to/connected to the new chimney, a shaft is built intended solely as a main channel for water/electricity.

Regarding FTX, we have recently installed district heating and definitely intend to completely rely on water-borne heat with radiators.

I think it sounds good with double vents in all rooms that require ventilation instead.

I'm not at all good with ventilation, and I need to study more before even approaching a decision on how to handle that issue.

 

[norrbottenstorpet]

Maybe like this:
Regarding FTX, we have recently installed district heating and definitely intend to rely entirely on hydronic heating using radiators.

I think it sounds good with double valves in all rooms that require ventilation instead.

I am not at all good at ventilation and I need to read up more before I even come close to making a decision on how I should handle that point..

A normal FTX system "pre-heats" only the incoming outdoor air with the heat from the outgoing "used old" air. It is an energy-efficient choice, regardless of the heat source.

(There are also more advanced alternatives such as exhaust air heat pumps that you might be thinking of, but that would hardly be a good choice when you are running district heating).

 

[ThomasN]

A normal FTX system "preheats" only the incoming outdoor air with the warmth from the outgoing "used old" air. It's an energy-wise good choice, regardless of the heat source.

(There are also more advanced alternatives such as exhaust air heat pumps which you might be thinking of, but that would hardly be a good choice when you're using district heating).

Aha, ok. Then it sounds interesting.