Unvented Cylinder - Summer Pressure Drop and Mfrs

[dumbrill]

Over the course of the week I changed my mind from fitting a heat only boiler and making minimal changes to getting an unvented cylinder fitted with a system boiler adjacent to it. Even with all the plumbing changes this is not significantly more work.

I've measured the water pressure and flow this morning and last night. The lowest reading was this morning at 3.7bar dropping to 0.9 with three mains taps running. With the three taps I got a total flow of 32l/min. Peak pressure was over 4 bar dropping to 1 bar when drawing 34l/min.

Unfortunately whilst the main to the house is new(ish), it's in 20mm MDPE and so I'm losing a lot of pressure along the 15m from the road. Increasing the size is not an option. Why anyone would fit a new 20mm pipe is beyond me!

Based on these results it looks as if an unvented cylinder will work. My question is whether there is typically a noticeable drop in pressure during the summer when water usage is (probably) higher?

Are there any makes of cylinder that I should avoid?

 

[Mark Br]

Yep especially at night just before dusk in my area

 

[ChrisR]

4 bar dropping to 1 bar when drawing 34l/min.

That's a very good flow rate, you'll be fine.
The "1 bar" depends entirely where you measure it of course.

Supply pressures tend to be more erratic if you're in the sticks, than in town.

 

[looneyfitter]

Ideally i would like to ensure that the hws main feed is in 22mm throughout the house with 15mm to basins/showers and 22mm to baths. Are you sure the MDPE is 20mm and not 25?

We live in a 5 bed house with 2 baths 2 showers. 25mm MDPE piped as above. Its been a while since i tested but from memory 1bar working pressure with 2 baths running and 14lm at each bath.

You will be fine. We have no probs with flow at our house.

 

[holty]

have known a few cases were unvented cylinders have been fitted. were the house was near a camp site. coarse come summer, you get a hell off difference in performance. i had the same problem when fitting a combi in st ives once. come summer the place is manic. and the use on water supply was noticable.

 

[dumbrill]

Ideally i would like to ensure that the hws main feed is in 22mm throughout the house with 15mm to basins/showers and 22mm to baths. Are you sure the MDPE is 20mm and not 25?

We live in a 5 bed house with 2 baths 2 showers. 25mm MDPE piped as above. Its been a while since i tested but from memory 1bar working pressure with 2 baths running and 14lm at each bath.

You will be fine. We have no probs with flow at our house.

The common pipework inside the house is already 22mm and no 2 taps share any 15mm, so it should be OK on that score.

The MDPE is definitely only 20mm because the bore is around 15mm. It's dropping the pressure by around 0.2bar per metre at the 34l/min!

What about cylinder manufacturers? Are there any ones to avoid? Or is it just a question of getting the longest guarantee / best price?

 

[looneyfitter]

Id go for a stainless one and stay clear of glass lined on my opinion. The santon prem plus is pretty impressive. Try and get one with twin coils too so your future proof if you wish to add Solar.

Gareth

 

[dumbrill]

Id go for a stainless one and stay clear of glass lined on my opinion. The santon prem plus is pretty impressive. Try and get one with twin coils too so your future proof if you wish to add Solar.

Gareth

I hadn't realised that there was an alternative to stainless. Anything else would seem like a false economy. What about the expansion side of things? Is the choice between an air gap or an external expansion vessel?

 

[looneyfitter]

iirc the oso and santon units have the option of gap or e pansion

 

[dumbrill]

iirc the oso and santon units have the option of gap or e pansion

I think it's the Telford Tornado and Tempest that are the two different types from one manufacturer.

I am probably going to go for a Santon, not least because the the warranty is better than the others. Fitting in the the expansion vessel is also no big deal in my case.

 

[Hessles]

Sorry to drag this one out of the grave

I have a very similar situation albeit with slightly better pressure. Would I be ok with an unvented cylinder?

Plan was to have a Veissmann system boiler and tank in the utility (next to the main stop cock) and run the 4 pipe system.

Craig