Insulating plastic CH pipes

[BloodAndBandages]

Just had our CH replaced (Boiler, rads, pipes - the works) in our house which has a suspended timber floor. After this was done, we had insulation installed underfloor - Knauf wool between the joists with plastic netting stapled to the joists.

The CH engineer was supposed to lag the pipes under the floor, but he's not keen to do it now as the insulation netting is over the pipes in most places, although the pipes are below the level of the joists. He had ample time to do it before the insulation went in.

As he has used plastic barrier pipe I understand that the heat loss won't be huge, but there will still be some heat loss. I'd say the chances of pipes freezing are remote, but I paid the guy to lag the pipes, so I believe he should do them.

Heating engineer says that there is only a 7 degree difference between the flow and return to the boiler, and lagging the pipes will make this even lower - I am told the ideal figure should be about 11 degrees.

Anyway, my thinking is that I don't want to be losing heat in the ventilated void under the floor!

I would be interested in your opinions on this.

 

[Dan Robinson]

I am told the ideal figure should be about 11 degrees

Should be nearer 20, but both you and he are misunderstanding why there should be a temperature difference.

Either way - any heat lost from the pipes is still useable heat in the dwelling so not really worth it unless they are passing through unoccupied areas or lofts.

 

[BloodAndBandages]

Should be nearer 20, but both you and he are misunderstanding why there should be a temperature difference.

Either way - any heat lost from the pipes is still useable heat in the dwelling so not really worth it unless they are passing through unoccupied areas or lofts.

I understand there should be a temperature difference because the heat should be 'lost' through the radiators - is that the right way to think about it? If it's really 7 degrees, what could be done to remedy that?

Most of the pipes are in the void under the floor, so outside the insulated envelope of the house - are you saying they are not really worth insulating?

 

[Dan Robinson]

If it's really 7 degrees, what could be done to remedy that?

Balancing the system properly and adjusting any bypass.

As for the thermal envelope... If the floor is in an occupied area then I wouldn't panic too much; but then we don't have much information to go on.

 

[motorbiking]

Sorry what?

maybe I'm missing something, but you have insulated pipes running through a vented floor void under your house with insulation between the joists above the plastic pipes?

I had a plumber do exactly the same and give me all sorts of BS why they don't normally do it.

Its a requirement for building control (though doesn't always get checked) and depending on how much unisulated pipe you have, may be the equiv. of mounting a radiator on the outside wall. I ended up digging the floor up and doing myself.

Something like ths :

and needs to be like this:

 

[Dan Robinson]

you have insulated pipes running through a vented floor void under your house with insulation between the joists above the plastic pipes?

Good point - can we clarify the order of constructions? Void, pipes, insulation, floor. Or Void, insulation, Pipes floor?

If the former - see my comments above. If the latter as per your & MB's suspicions .

 

[BloodAndBandages]

We have a suspended timber floor which has vents all round the house, so it's a cold space. The floor itself has Knauf roll insulation between the joists. Underneath the insulation (i.e. in the cold space, outside the thermal envelope of the house!) we have uninsulated plastic central heating pipes going to the radiators, plus hot water taps in bathroom and kitchen.

My reckoning is that they should be insulated as they will be losing heat - the analogy of mounting a radiator on the outside wall is accurate!

The heating engineer can't be bothered doing it because the netting for the insulation covers the pipes in a lot of places, although the insulation doesn't cover the pipes as they are below the joists. He claims not much heat is being lost as there is only a 7 degree difference between flow and return of the boiler. If this is true then I think this must be some other problem - I do not want to be heating the void under the floor!

So going down the way, we have floor, insulation, CH pipes.

 

[oldbuffer]

1. The rate of heat loss from a pipe (or anything else) is directly proportional to the difference in temperature between the pipe and its surrounding material. Its nothing to do with the difference between flow and return temperatures.
2. There will be a heat loss from your uninsulated pipes. However, providing those pipes are below rooms which are used, then that heat is eventually going to rise into those rooms. Insulation does not prevent heat loss, it only slows it down.
3. Yes, they should have been insulated. To an extent they will be insulated by the Knauf insulation. You might prefer to negotiate a rebate on the price rather than have the hassle of getting an unwilling person back to do a job which is, in my opinion, of minor importance.
4. The cold water and domestic hot water pipes should be insulated, the former to reduce the risk of freezing, the latter to reduce the amount of water wasted before hot appears at the taps.

 

[BloodAndBandages]

2. There will be a heat loss from your uninsulated pipes. However, providing those pipes are below rooms which are used, then that heat is eventually going to rise into those rooms. Insulation does not prevent heat loss, it only slows it down.

While the pipes are below rooms that are being used, there is a layer of knauf insulation between them and the rooms - the heat will mostly be lost through the underfloor vents - I would say very little of it would find its way to the rooms above.

 

[BloodAndBandages]

To clarify, there are air bricks in the wall below floor level, to ventilate the underfloor void.

 

[BloodAndBandages]

Sorry what?

maybe I'm missing something, but you have insulated pipes running through a vented floor void under your house with insulation between the joists above the plastic pipes?

I had a plumber do exactly the same and give me all sorts of BS why they don't normally do it.

Its a requirement for building control (though doesn't always get checked) and depending on how much unisulated pipe you have, may be the equiv. of mounting a radiator on the outside wall. I ended up digging the floor up and doing myself.

Something like ths :

and needs to be like this:

Your underfloor space is much smaller than mine and it doesn't seem to have insulation under the boards - just rememebred I took some snaps at the weekend so I will put some up.

 

[BloodAndBandages]

Here are some snaps I took the other day - I just remembered I have them on my phone!

 

[motorbiking]

As a rough estimate you seem to have well in excess of 50M of polyipe in an uninsulated floor void. my void at its deepest is about 2/3rds the height of yours. I'd estimate you are losing at least 1.5KW of energy. The risk isn't the pipe freezing its the energy wasted heating pipes that are outside your living space.

See :
http://webarchive.nationalarchives....mestic_building_services_compliance_guide.pdf

Table 5 P20 (as printed Minimum standard
a.
Pipes should be insulated to comply with the maximum permissible heat loss indicated in the Supplementary
information column, and labelled accordingly,
a follows:
i. Primary circulation pipes for heating circuits should be insulated wherever they pass outside the heated living space or through voids which communicate with and are ventilated from unheated spaces.

Don't let him off the hook this will completely negate any insulation that has been fitted and probably increase your heating costs 10-20%

 

[BloodAndBandages]

As a rough estimate you seem to have well in excess of 50M of polyipe in an uninsulated floor void. my void at its deepest is about 2/3rds the height of yours. I'd estimate you are losing at least 1.5KW of energy. The risk isn't the pipe freezing its the energy wasted heating pipes that are outside your living space.

I'd say 50M is a low estimate - there are 9 radiators serviced on the ground floor. I agree that I must be wasting a lot of heat under the floor!

I will get back on his case and insist that he finishes the job I paid him for!

 

[motorbiking]

It makes my blood boil at these so called plumbers (and most plumbers are very good)- but with some they seem to be clueless. mine was a complete ******. I ended up having to redo loads and still had leaks to deal with after he'd left causing me to have to repair brand new ceilings twice.

I'm afraid you've got the equv of two radiators mounted outside your house. If you have a temp sensor take the temp of the flow pipe from the boiler and the temp of the flow pipes at each ground floor rad. You'll then realise how much you are losing.