Loft temperature

[MNW67]

With three very cold nights forecast, I thought I might monitor the loft temperature with a couple of thermometers I trust. I had no idea what to expect. In these parts it has been hovering around freezing all day, and the loft is 4C at midnight. I'll be interested to see what happens if the weather gets down to minus 8 as forecast.

The loft is boarded and we have 150mm of insulation between the joists. It's a two storey detached built circa 1990.

 

[motorbiking]

Better to use an IR monitor to see if you have any thermal bridging or gaps in insulation

 

[MNW67]

Apart from general interest, I was also thinking about the pipes. It occurred to me that usually there is no flow through the pipe which tops up the header tank. I worked out that if the loft gets down to -3C for 13 hours it will freeze solid.

 

[motorbiking]

150mm of insulation and a below room temperature of say 15 degrees. Says that would be unlikely.

 

[MNW67]

I don't actually know what the relevant scientific principle is here. There is heat loss from the uninsulated roof to the sky and then there is heat loss through the insulated ceiling into the loft. I can work out one or the other, but I can't get my head round both together. So I thought it would be easier just to measure it!

 

[motorbiking]

Are they lagged?

 

[MNW67]

Yes, standard 15mm pipe insulation. As far as I can tell, that roughly halves the heat loss. That was included in my figures above.

 

[Harry Bloomfield]

Apart from general interest, I was also thinking about the pipes. It occurred to me that usually there is no flow through the pipe which tops up the header tank. I worked out that if the loft gets down to -3C for 13 hours it will freeze solid.

Your loft temperature, will not be that representative of the temperature your pipes and tanks are subjected to, unless your house has no heating for a considerable period of time. Your pipes and tanks, should have insulation above them, and none below, so they get the benefit of house heat rising from below.

More representative, would be to measure the temperature of the water in the tank itself. I continuously log, as I have done for years, the general house temperature, at a particularly cold place, the landing. Last night, the CH went off at 10pm (or more accurately, set back to 14C), with it recording 18.1C. By this morning, and getting up, and the CH again set for 18C - the lowest the temperature had fallen to, was 16.9C. Obviously, overnight, with the heating setback at 14C, the boiler hadn't needed to fire.

 

[MNW67]

Your loft temperature, will not be that representative of the temperature your pipes and tanks are subjected to, unless your house has no heating for a considerable period of time. Your pipes and tanks, should have insulation above them, and none below, so they get the benefit of house heat rising from below.

More representative, would be to measure the temperature of the water in the tank itself. I continuously log, as I have done for years, the general house temperature, at a particularly cold place, the landing. Last night, the CH went off at 10pm (or more accurately, set back to 14C), with it recording 18.1C. By this morning, and getting up, and the CH again set for 18C - the lowest the temperature had fallen to, was 16.9C. Obviously, overnight, with the heating setback at 14C, the boiler hadn't needed to fire.

My thermometers are actually on the tank table and right next to the pipe in question. I am hoping that gives an accurate enough measurement of the surrounding air temperature.

There is insulation under the tanks and it can't really be accessed to be removed.

Wouldn't the water in the tank take a long time to change temperature? There would be a lot of lag?

It has been colder before, but not for several nights in a row. If I see the temperature at the tank table drop really low I will just open the hatch. But mainly I am just interested in the observations.

 

[Harry Bloomfield]

My thermometers are actually on the tank table and right next to the pipe in question. I am hoping that gives an accurate enough measurement of the surrounding air temperature.

Better, would be to get the probe against the side of the tank, and under/covered by the insulation. If it's the hot water header tank, and the house is occupied, likely there will be a regular flow of slightly water entering, from the mains.

Pipe-work, because of the much smaller water content, are much more at risk of freezing, than tanks.

 

[MNW67]

If it's the hot water header tank, and the house is occupied, likely there will be a regular flow of slightly water entering, from the mains.

Indeed. The only pipe I would be slightly worried about would be the one to the central heating header tank because I believe that can go a very long time without any water moving in it. All the other pipes have water flowing through them regularly.

 

[Andy165]

Put your loft insulation over your insulated pipework and your header tank. Belt and braces approach.

 

[Harry Bloomfield]

Indeed. The only pipe I would be slightly worried about would be the one to the central heating header tank because I believe that can go a very long time without any water moving in it. All the other pipes have water flowing through them regularly.

By design, or accident - the branch leading off my supply to the HW tank, to the F&E tank, is quite short, so less likely to freeze.