OK, so from a search and a chase, this appears to be a somewhat controversial topic 
Anyway, I'm looking at lagging various central heating pipes. These are your pretty standard central heating pipes, and mostly drop from the ceiling to feed rads. There's somewhere in the region of 20m of uninsulated pipework like this.
One of the online calculators has provided me with an approximate heat loss figure of 22.1 BTU/h per foot of pipe, using a flow temp of 65c (The boiler setpoint is 70c, but I think this is a reasonably approximation of the temperature across the system)
Assuming a 2m drop, this is then ~147 BTU/h for one leg of the drop. Then assuming that it takes around 30s to flow down the 2m drop, I get a heat loss of ~1.2 BTU/h, or therefore a drop of about 0.5c in my flow temp for each leg of the drop, not counting the heat given out by the radiator.
Now as I see it, adding on pipe insulation to this example run will reduce the heat loss to basically nil.
The argument I'm seeing is that leaving these pipes unlagged will add to the room temperature, but as far as I can see that's actually not the whole picture.
By increasing the temp in my rad, this will a give a corresponding increase in heat transfer efficiency across a much greater surface area than in the pipes that I've just insulated. This increase is likely to be increased (Not exponentially, I'm not sure by how much) over the course of the 5 radiator circuit, as each rad gets hotter water. I can probably assume that the boiler cycle time would be increased too, as the return temp goes up
We can probably also assume that at least 50% of the heat lost by the pipe is actually 'useless', as it's either right the way up at ceiling level, or radiated into the walls. (All the rads and pipes are stuffed into corners). Again, we're not going to get 70% of this 50% back, but every little helps
I suspect the actual savings from doing this are likely to be marginal, perhaps a 5- 10% notional saving, rather than the headline 70% heat loss saved figure. The same calculator gives me a payback time of somewhere in the region of 90 days at a 6p/ kwH & £20 materials cost, so I'd be guessing in the region of three years plus to see any payback.
Anyone with any interesting thoughts on my musings?
The time based calculations are possibly (probably!) on the generous side, but energy costs are only going to keep going up, and this only gets done once.
(Sorry, this post has been edited several times to make myself clearer!)
-Leezer-
Anyway, I'm looking at lagging various central heating pipes. These are your pretty standard central heating pipes, and mostly drop from the ceiling to feed rads. There's somewhere in the region of 20m of uninsulated pipework like this.
One of the online calculators has provided me with an approximate heat loss figure of 22.1 BTU/h per foot of pipe, using a flow temp of 65c (The boiler setpoint is 70c, but I think this is a reasonably approximation of the temperature across the system)
Assuming a 2m drop, this is then ~147 BTU/h for one leg of the drop. Then assuming that it takes around 30s to flow down the 2m drop, I get a heat loss of ~1.2 BTU/h, or therefore a drop of about 0.5c in my flow temp for each leg of the drop, not counting the heat given out by the radiator.
Now as I see it, adding on pipe insulation to this example run will reduce the heat loss to basically nil.
The argument I'm seeing is that leaving these pipes unlagged will add to the room temperature, but as far as I can see that's actually not the whole picture.
By increasing the temp in my rad, this will a give a corresponding increase in heat transfer efficiency across a much greater surface area than in the pipes that I've just insulated. This increase is likely to be increased (Not exponentially, I'm not sure by how much) over the course of the 5 radiator circuit, as each rad gets hotter water. I can probably assume that the boiler cycle time would be increased too, as the return temp goes up
We can probably also assume that at least 50% of the heat lost by the pipe is actually 'useless', as it's either right the way up at ceiling level, or radiated into the walls. (All the rads and pipes are stuffed into corners). Again, we're not going to get 70% of this 50% back, but every little helps
I suspect the actual savings from doing this are likely to be marginal, perhaps a 5- 10% notional saving, rather than the headline 70% heat loss saved figure. The same calculator gives me a payback time of somewhere in the region of 90 days at a 6p/ kwH & £20 materials cost, so I'd be guessing in the region of three years plus to see any payback.
Anyone with any interesting thoughts on my musings?
The time based calculations are possibly (probably!) on the generous side, but energy costs are only going to keep going up, and this only gets done once.
(Sorry, this post has been edited several times to make myself clearer!)
-Leezer-
