Some considerations when fitting a combi in a roofspace.
There is a risk of freezing when putting a metal object filled with water in an unheated space
Frost stats don’t work in a power cut.
Antifreeze in the heating system doesn’t protect the domestic hot and cold pipework.
You’re also relying on a low pressure switch (if there is one) to shut the boiler off if there is an escape of water from the system or pressure relief valve to stop the boiler running while empty.
Sure the householder might like to win some space in a kitchen or airing cupboard but unless they’re agile (fit that is, not the poster to this site) the customer can have trouble getting to the thing to operate it or see the pressure gauge or fault codes and unless the loft is boarded and lit. It can also be risky.
Another big consideration however is the fact that the source of hot water is situated so far away from the point at which it’s used most; the kitchen sink (first floor bathrooms are used less often of course in most households).
Unless you locate the boiler in a neighbour’s house it’s about as inefficient an arrangement as you can get.
Knowing the limitations on my own math it’d be advisable to check this yourself but if 1m of 15mm contains .176 litres and the distance from combi to sink is 20m every time the sink tap is run 3.5 litres of cold water is wasted and the customer has to wait the time it takes to run it off before the hot gets to the tap.
What’s worse of all however is that when the hot water finally arrives and has been used the tap is then of course turned off and 3.5 litres of perfectly good hot water sits in the pipe and grows cold. Plus the water in the boiler and heat exchanger, say six litres.
If the client runs the kitchen sink tap 20 times a day 120litres are heated and not used.
At 2008 prices this equated to around £40 a year (more now) – a customer’s money spent for nothing except waste of their fuel, water and time.
If any of the hot water pipework is 22mm the losses are even higher.
Locating a hot water storage cylinder far away from the point of use is also a practice to be avoided for the same reasons plus that of standing heat loss from the cylinder.
There is a risk of freezing when putting a metal object filled with water in an unheated space
Frost stats don’t work in a power cut.
Antifreeze in the heating system doesn’t protect the domestic hot and cold pipework.
You’re also relying on a low pressure switch (if there is one) to shut the boiler off if there is an escape of water from the system or pressure relief valve to stop the boiler running while empty.
Sure the householder might like to win some space in a kitchen or airing cupboard but unless they’re agile (fit that is, not the poster to this site) the customer can have trouble getting to the thing to operate it or see the pressure gauge or fault codes and unless the loft is boarded and lit. It can also be risky.
Another big consideration however is the fact that the source of hot water is situated so far away from the point at which it’s used most; the kitchen sink (first floor bathrooms are used less often of course in most households).
Unless you locate the boiler in a neighbour’s house it’s about as inefficient an arrangement as you can get.
Knowing the limitations on my own math it’d be advisable to check this yourself but if 1m of 15mm contains .176 litres and the distance from combi to sink is 20m every time the sink tap is run 3.5 litres of cold water is wasted and the customer has to wait the time it takes to run it off before the hot gets to the tap.
What’s worse of all however is that when the hot water finally arrives and has been used the tap is then of course turned off and 3.5 litres of perfectly good hot water sits in the pipe and grows cold. Plus the water in the boiler and heat exchanger, say six litres.
If the client runs the kitchen sink tap 20 times a day 120litres are heated and not used.
At 2008 prices this equated to around £40 a year (more now) – a customer’s money spent for nothing except waste of their fuel, water and time.
If any of the hot water pipework is 22mm the losses are even higher.
Locating a hot water storage cylinder far away from the point of use is also a practice to be avoided for the same reasons plus that of standing heat loss from the cylinder.
I'd love to see someone trying to cram a 50kg boiler through my loft hatch 
