Feasibility of Vented for new build….

[Iceverge]

6 hours ago, G and J said:

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

 

Yes. I'm sure you can pay a plumber but if everything is easily accessible you could do it in 5 mins. 

 

4 hours ago, JohnMo said:

You don't want to oversize the cylinder as you need more legionella cycles

 

Not necessarily true. You could just store the water at a lower temp (also better for COP) and use less cold water to blend it to shower temperature. With this you would still cycle the entire volume of water in the cylinder as frequently as the a smaller cylinder at higher temps.  From my quick calcs a 210l cylinder at 55⁰ has the same amount of useable hot water as a 300l cylinder at 47.5⁰ but buying the big cylinder gives you the option of 43% more hot water if you heat it to 55⁰ for guests etc. 

 

4 hours ago, JohnMo said:

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.

 

I completely agree. It's an excellent system. Don't forget you are building a house in the real world. Material available is vital. 

 

4 hours ago, G and J said:

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.

 

 

Why not do all 3 electric UFH, electric towel rads and wet UFH. The cost will be small. Use a simple timer for the electric bits. Given you are planning a low energy house the UFH and towel rads would probably be enough as a back up heating system anyway should the ASHP fail. 

 

 

 

 

[Kelvin]

37 minutes ago, Iceverge said:

 

What's wrong with both? 

 

 

Nothing if you’ve planned for it. By the time I realised it’s what we should have done it was a bit late to change it. We’re tiled throughout and it would have meant a a slightly different height between the downstairs bathroom floor and the hallway which I didn’t want. We do have an electric towel rail which I installed today coincidentally. 

Edited June 24 by Kelvin

[G and J]

2 hours ago, JohnMo said:

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.

So if I have an ASHP and I want to benefit from a warranty I have no choice.  Sod.

 

At the start of this thread I asked “Am I missing something glaringly b obvious…”

 

I now know the answer to that one lol

[G and J]

2 hours ago, Kelvin said:

You’ve not really explained why you think vented is preferable other than your familiarity with it

Well, I do think going with a personal preference, all other things being nearly equal, is valid, so that’s a biggie for me.

 

There is some history here.  In ‘91 I fitted a gravity (much nicer term than vented) system with an oil boiler that’s still going.  In 33 years (touch wood) I’ve had to replace one valve, the ball valve in the loft as it got noisy.  Easy peasy.

 

I’ve also had installed various pressurised (much more honest term than unvented, I prefer to call a spade a flippin shovel) systems in various properties that have had to have regular professional involvement.  Downtime, guest/tenant angst, cost, hassle.  OK that’s all been gas boiler based and maybe it’s not representative of the likely experience in our new pad, but it’s still my backdrop.

 

I’m also aware that I don’t have as much irritating and pointless box ticking with gravity systems.   Sigh.

[G and J]

1 hour ago, Iceverge said:

 

Why not do all 3 electric UFH, electric towel rads and wet UFH.

I get the electric towel rail.  But the doubling up on the UFH seems daft to me, even if the COP is poor when heating just the bathrooms it won’t be less than 1, and it can’t be hard to have a second zone for just the three bathrooms and as you say, at certain times of year, courtesy of the MVHR that’ll do the whole house.  
 

1 hour ago, Iceverge said:

back up heating system anyway should the ASHP fail.

And that’s the woodburner…

[JohnMo]

40 minutes ago, G and J said:

So if I have an ASHP and I want to benefit from a warranty I have no choice.  Sod

You can can still have a vented cylinder i.e. tap water. The heating system for your UFH and heating the cylinder is pressurised, ie the bits connected to the heat pump.

[G and J]

29 minutes ago, JohnMo said:

You can can still have a vented cylinder i.e. tap water. The heating system for your UFH and heating the cylinder is pressurised, ie the bits connected to the heat pump.

Hmmm, true, but would it be better to accept that the tide is coming in and rather than one of each type system just pressurise the lot and go with current bog standard….?

[JohnMo]

1 minute ago, G and J said:

Hmmm, true, but would it be better to accept that the tide is coming in and rather than one of each type system just pressurise the lot and go with current bog standard….?

Yep. I did a course at the local college for Unvented Cylinders and did my own. 1/2 day all done.

[G and J]

1 hour ago, JohnMo said:

Yep. I did a course at the local college for Unvented Cylinders and did my own. 1/2 day all done.

Presumably you still had to get the install signed off by a G3 person…..?

[JohnMo]

27 minutes ago, G and J said:

Presumably you still had to get the install signed off by a G3 person…..?

No I am as qualified as any one else, I am the G3 competent person. So can do my own or anyone else's sign off. Our council were not interested in the UVC being registered with themselves.

[Iceverge]

5 hours ago, G and J said:

get the electric towel rail.  But the doubling up on the UFH seems daft to me, even if the COP is poor when heating just the bathrooms it won’t be less than 1, and it can’t be hard to have a second zone for just the three bathrooms and as you say, at certain times of year, courtesy of the MVHR that’ll do the whole house.  

 

Electric UFH isn't really a space heating device IMO, more of a comfort thing. 

 

I you rightly bury wet UFH pipes in a thick screed then the heat up and cool down times are going to be unsuited to just delivering a small comfort improvement to the tiles for those morning showers in the shoulder months. 

 

You'll end up either delivering too much energy to the house and overheating it or else not noticing the difference. 

 

A high wattage UFH matt literally just under the tiles will have very little thermal inertia, it will heat up quickly, and cool down quickly without actually adding too much energy to the building but it will make your toes feel nice and toasty and dry the room out swiftly too.