Feasibility of Vented for new build….

[G and J]

Back in ‘91 I plumbed our house.  Oil boiler in garage, hot water cylinder in airing cupboard, steel rads in most rooms, two tanks (little and large) in the loft. 

 

Showers have about 6’ head, and are fed by 22mm both hot and cold the cold being direct from loft tank to balance the pressures.  They still work well, so assuming Aqualisa make similar I’ll be replicating as yes, I want to go vented. 

 

That way I can install and maintain, I’ve space in the right place in me loft and I do like simple. 

 

I (or someone) will be putting in an ASHP which will run the UFH and DHW. I might go a bit space age and fit a stirry up pump thingy, as I think that effectively increases the hot water capacity of a system, I’ll look into that in due course. 

 

One thing I’d improve (meaning reduce) if I could on my current system is the amount of water drawn to get hot water to each bathroom.  I foolishly did some of the DHW distribution in 22mm copper and the rest in 15mm.  

 

Another thing I would improve is having no buried joints.  I have dozens of solder joints buried in floors, etc. so the idea of using manifolds and continuous plastic pipes so every joint remains accessible appeals.  

 

I’ve read just about all I could find on here re vented vs unvented and I remain convinced that I like vented.  I note however that the world quietly went unvented over the last three decades.  

 

First question.  Am I missing something glaringly b obvious in concluding vented is ok for my new house?

[Iceverge]

The only satisfactory vented solution is a coil in tank thermal store in my opinion. 

 

I installed a 250l Maxi Pod TS to combine the oil boiler and perpetually running solid fuel Rayburn in my parents house. It works really well but needs to be kept above 65-70⁰.  

 

It would work equally well with a new build oil or gas system boiler. 

 

However......

 

In a low energy demand house, the high storage temperatures may cause  localised overheating near the tank. Not an issue in an old farmhouse. 

 

An ASHP won't be able to provide high temp water at a reasonable COP for the store. You can compensate by having a very very big thermal store. Daikin have an off the shelf product, I can't see why it shouldn't work. 

 

We did a simple immersion in 300l unvented cylinder (UVC). It provides sufficient water for us on cheap night rate electric. It should prove very economical once I eventually install PV and a divert. 

 

 

 

[Iceverge]

Meanwhile these are my problems and not your solutions.  

 

From my time on this forum, for your house I would recommend . 

 

1. A 5kW monoblock ASHP. 

2. A 300l ASHP UVC. 

3. Hep20 push fit plumbing with the hot manifold preheated by convection above the cylinder. Pipes run in a radial fashion. 15mm for the baths, showers, and kitchen sink and 10mm for everything else. 

3. In slab wet UFH in a single zone downstairs. 

4. Electric UFH in all bathrooms. 

5. Floor drains with waterless traps in every wet room for leak protection. 

 

 

G3 checks are simple. Just clean the filter, pressurise the expansion vessel and check the temp and pressure valves. I do my own. 

 

 

 

[G and J]

Interesting how similar our thinking is….

 

1. A 5kW monoblock ASHP.
TICK!

 

2. A 300l ASHP UVC.

I was thinking 300l ish, but vented.  I believe they exist. 
 

3. Hep20 push fit plumbing with the hot manifold preheated by convection above the cylinder. Pipes run in a radial fashion. 15mm for the baths, showers, and kitchen sink and 10mm for everything else. 

I’ve plumbed with Hep20 successfully before, and I’m happy to do so again - my plan is to work it so that no joints are buried - will be mostly radial.  Pipe size perhaps depends on whether I go vented.  

 

3. In slab wet UFH in a single zone downstairs.

TICK

 

4. Electric UFH in all bathrooms. 

Ah, we’re thinking wet UFH in upstairs bathrooms.  
 

5. Floor drains with waterless traps in every wet room for leak protection. 

Haven’t thought about this but yet. 

[dpmiller]

Another vote here for a TS, and it's my experience that the inefficiencies that some folk mention are somewhat overdramatic

[G and J]

3 hours ago, Iceverge said:

G3 checks are simple. Just clean the filter, pressurise the expansion vessel and check the temp and pressure valves. I do my own. 

So you are effectively saying that UV is dead simple to maintain?

[G and J]

3 minutes ago, dpmiller said:

Another vote here for a TS, and it's my experience that the inefficiencies that some folk mention are somewhat overdramatic

Sorry to be dumb but presumably a Thermal Store is different in some way to a hot water cylinder?

[scottishjohn]

If you want no joints in plumbing  walls then uponor  piping system is your best option 

 bends are just made bylatying easy bends in the piping.

you can get 90degree fittings if you want and change over fitting to copper or normal hep2  --what ever you wish to do 

you strech the pipe with a special tool and  push it onto serated fitting with a collar which also gets streched  -then in next minute or less it shrinks back onto the fitting - no way they will ever leak 

i was going to go that way when iwas going to do the whole build myself 

but age and infirmarty made that a non starter 

I have the miwaukee tool for doing that if you are interested 

rolls of pipe can be 100m long 

https://uk.video.search.yahoo.com/search/video?fr=mcafee&ei=UTF-8&p=uponor+pipe&type=E210GB1494G0#id=83&vid=6c5044b14d120022e0c5ece74781b587&action=view

Edited June 24 by scottishjohn

[G and J]

44 minutes ago, scottishjohn said:

If you want no joints in plumbing  walls then uponor  piping system is your best option 

 bends are just made bylatying easy bends in the piping.

you can get 90degree fittings if you want and change over fitting to copper or normal hep2  --what ever you wish to do 

you strech the pipe with a special tool and  push it onto serated fitting with a collar which also gets streched  -then in next minute or less it shrinks back onto the fitting - no way they will ever leak 

i was going to go that way when iwas going to do the whole build myself 

but age and infirmarty made that a non starter 

I have the miwaukee tool for doing that if you are interested 

rolls of pipe can be 100m long 

https://uk.video.search.yahoo.com/search/video?fr=mcafee&ei=UTF-8&p=uponor+pipe&type=E210GB1494G0#id=83&vid=6c5044b14d120022e0c5ece74781b587&action=view

Just googled it - so it’s the same system one uses for wet underfloor heating it appears.  Interesting economy of scale if using the same tools and pipe for both….

[Kelvin]

I used the Rehau smart manifold system. It wasn’t cheap and requires a couple of special tools to form the joints which the supplier hires out. Very happy with it. It’s very neat, the joints are good, the pipes are very robust. It’s very quick to install. Took a day to pull all the pipe through the house and connect to the manifold.  I made one mistake and cut the pipes too short in the utility room so was unable to form them through the wall so I ended up having to make two joints in the wall. 
 

 

 

[JohnMo]

We have a 210L slimline UVC never run out of water (2 of us). Done combi boiler, unvented, really no way I would go back to unvented. Everything is hygienic all water is drinking quality with an UVC, no overhead tank, that no one looks for decades at a time, no thanks, full of stale water or worse etc.

 

You don't want to oversize the cylinder as you need more legionella cycles. Vented I would be doing every day, unvented I never do it because we move enough water through the cylinder, so no risk. As mentioned the other option is a TS or the new cylinder from Heat Geek, requires no G3 and supplied DHW via a coil at mains pressure. It is also small in size. A thread on it on this forum and videos online.

 

Hep2O is simple, easily available on a Sunday morning if you run out of a bit. The good thing is the reinforcing push-in piece at the joints is very thin metal so you have less flow restrictions. A manifold for hot and cold is best thing we installed, allows rooms to be commissioned one at a time without interrupting the others.

 

UFH pipes, pert-al-pert nothing else, decent manifold. Heat pump don't buy one that is NOT able to cool also.g

 

Your heating system will have to be pressurised, to get a start enable.

 

We have wet UFH in wet rooms, and electric towel radiators. You need something in addition to the house heating as your house heating is likely to off house comfortable but bathroom not so comfortable.

 

[G and J]

21 minutes ago, JohnMo said:

Your heating system will have to be pressurised, to get a start enable

Sorry JohnMo, I don’t understand what that means.

 

22 minutes ago, JohnMo said:

We have wet UFH in wet rooms, and electric towel radiators. You need something in addition to the house heating as your house heating is likely to off house comfortable but bathroom not so comfortable.

We are thinking along the same lines, for the same reason we’ve put an electric towel rail in our en-suite so it’s warm when the heating isn’t needed.  J loves warm, soft towels.

 

24 minutes ago, JohnMo said:

210L slimline UVC never run out of water

Do either of you have a very eco-unfriendly bath habit?  I know I do.

[G and J]

47 minutes ago, Kelvin said:

I used the Rehau smart manifold system

May I ask why that rather than other systems?

[Kelvin]

The pipes and they way the joints are made are more robust than the other systems I looked at, you don’t need to worry about scratching the outside of the pipe when pulling through the building albeit I was still careful, the manifolds are very neat and I had limited space in the plant room. The pipe is less flexible than the Hep stuff so you need to be careful with how you route it as pushing it around other stuff isn’t easy so I put it in first. 

[JohnMo]

20 minutes ago, G and J said:

either of you have a very eco-unfriendly bath habit?  I know I do.

Wife does occasionally, she used to most days in the last house, but doesn't so often in this one. May be a different feel to the house

 

21 minutes ago, G and J said:

Sorry JohnMo, I don’t understand what that means.

 

9 hours ago, G and J said:

two tanks (little and large) in the loft. 

Your heating system will not have a tank in the loft, it will be pressurised to about 1 bar. So you little tank won't be there with a heat pump.

[Kelvin]

It’s very easy to use as much water showering as you do in a bath. 

[Sparrowhawk]

We have just had our system replaced, switching from a vented to unvented cylinder (UVC). I was skeptical (and still am tbh) but everyone we got to quote wanted to do it, so we did.

 

Our taps and showers were powerful enough before, but the showers were those electric pumped ones that suck water through from the hot water tank. The biggest difference with the UVC is how quiet a shower now is without that pump and the racket it caused in the pipes. That silence alone is almost worth the extra £1k an UVC setup cost us.

 

I can't add anything about tank size as we replaced the gas boiler with another gas boiler and went for a smaller tank (180l) and a priority hot water setup and it isn't bath season yet, but the tank reheats quickly so I've no concerns. For winter baths I can always raise the tank temperature.

 

One thing I'd do differently if doing it again is tank choice. I left it to the heating engineer and he provided a 'B' rated tank, and the heat loss is higher than I was hoping for. I'll fit extra insulation around it but would have been easier to have a more efficient tank to start with.

[G and J]

1 hour ago, Kelvin said:

The pipes and they way the joints are made are more robust than the other systems I looked at, you don’t need to worry about scratching the outside of the pipe when pulling through the building albeit I was still careful, the manifolds are very neat and I had limited space in the plant room. The pipe is less flexible than the Hep stuff so you need to be careful with how you route it as pushing it around other stuff isn’t easy so I put it in first. 

Noted. Thank you. 

[G and J]

1 hour ago, JohnMo said:

Your heating system will not have a tank in the loft, it will be pressurised to about 1 bar. So you little tank won't be there with a heat pump.

Ummm, so do all heat pumps require unvented?

 

In my infinite stupidity I see no reason why they would.  

[Kelvin]

I can’t emphasise enough how flexible any manifold based water distribution system is. As @JohnMo says the ability to commission everything one tap at a time really helped us. 

[G and J]

1 hour ago, Kelvin said:

It’s very easy to use as much water showering as you do in a bath. 

When I bath (I am a hippo!) I leave little hot water.  When J showers (she very definitely is not a hippo!) it leaves loads of hot water, so I’m designing around my bad habits lol

[JohnMo]

1 hour ago, Sparrowhawk said:

left it to the heating engineer and he provided a 'B' rated tank, and the heat loss is higher than I was hoping for. I'll fit extra insulation around

I would just store at 55 to 60, with a gas boiler reheat time will be about 10 mins, your losses will be negligible. More important is suitable insulation on the pipework that will loose way more than the cylinder. Best bang for the buck is always choose a heat pump cylinder for any heat source. Fast reheats, gas boiler nearly condense all the time for added efficiency.

 

49 minutes ago, G and J said:

 

In my infinite stupidity I see no reason why they would

Air in system causes corrosion of the heat exchanger, less efficient heat exchange throughout the system.

44 minutes ago, G and J said:

Ummm, so do all heat pumps require unvented?

Yes every instruction manual I have read (I like reading manuals) has required piping that is not air permeable and to be pressurised. I am talking heating water not fresh water.

 

 

[Kelvin]

You’ve not really explained why you think vented is preferable other than your familiarity with it. The requirement for an ASHP has likely made the decision for you however. 
 

On the wet UFH upstairs comment. Many of us on here haven’t bothered taking the wet heating upstairs. Some folk pipe for it a lot don’t bother and just have sockets in the right places for panel heaters or such like in case they are needed on very cold days. Electric UFH in small bathrooms is an easy and straightforward install that minimises the depth of floor build up albeit there’s still quite a bit of extra depth (insulated board, UFH mat, screed, adhesive, tile) You shouldn’t really need to heat the room with it, it’s more to make it comfortable. More importantly you want to isolate this from your wet heating system anyway as your likely to want to heat the bathroom outside of the general heating season. We took the wet UFH into the downstairs bathroom and this was a mistake in hindsight. We should have just used electric UFH in here.

[Iceverge]

1 hour ago, Kelvin said:

We took the wet UFH into the downstairs bathroom and this was a mistake in hindsight. We should have just used electric UFH in here.

 

What's wrong with both? 

 

 

[JohnMo]

3 minutes ago, Iceverge said:

 

What's wrong with both? 

 

 

Easy enough at the build stage. Wet UFH below screed, electric above.