Help me choose the right system - Please

[mark740]

Guys,

I know this has probably been done to death but i cant seem to nail this down.

Just to give you some background, i am not a plumber obviously but have read as much as i can to help myself.

I currently have a conventional Gravity fed system with a Baxi back-boiler, I recently had an extension built with 20sqM of wet underfloor heating fitting, the rest of the house remains on traditional radiators.
I have 2 bathrooms both with showers, upstairs is pumped and downstairs is gravity fed.

Currently the system seems to work just fine, radiators work as and when i need them, the underfloor heating is fed via its own zone and valve and has its own wireless (honeywell 927) programmer/thermostat, i was assured that the boiler i have was fine for this new underfloor system but i think it cycles a little too often but that's another problem.

I really want to remove my chimney breast which in turn means i will need a new boiler, now im split between what system to get, I would like a combi for reasons of space saving and instant water but as i have 2 showers (which are not regularly used together but it does happen occasionally)and the underfloor heating ( will a combi modulate down low enough for jsut the underfloor as for all but the coldest few months is more that adequate to heat the entire downstairs)
Alternatively its the system boiler and sealed tank, but this comes with its issues in my house ( i think... )i still have a lead water main, but i have really high pressure....so high that the garden hose has to have a PRV to stop it popping the fittings off the hose ( yes really) high pressure is good i think but the lead pipe i would have thought will affect the dynamic flow rate ?? (small bore pipe) also i believe this system requires some sort of pressure relief pipe....which i am not sure could work for me ??

i would have to have the boiler in the loft as i don't have an exterior wall to allow for a flue to be fitted, i just want to make sure i choose the best system for me, i have had really bad experiences in the past with plumbers so just want to make sure i know what's what's before getting some quotes

I know that's a very long post but thanks in advance for any help you can give me.

Edit - sorry I totally forgot to actually ask some defined questions ,

Other than the usual combined v stored system pros and considered is there any reason to chose one over the other because I am.mixing both underfloor heating and rads ?

Can I have both boilers in the loft ? From reading I think I can but the only place for a cylinder if I go that way is under the stairs (its current position)

mark

 

[ScottishGasMan]

Firstly, theres not perfect option for most systems, there will always be a bit of give and take whatever you go for when retro fitting as opposed to being able to strat a whole house from scratch.

Personally, I would choose the System boiler and Unvented Cylinder option. You keep the advantage of stored hot water at a rate that can feed two showers, and a much smaller boiler can be used so less cycling on and off and also a smaller gas pipe run required to the boiler in loft.

With regards to the mains pipe, what flow rate can you get out the garden hose tap? pressure it one thing, but is it a good flow when its running? if so I wouldnt worry too much about the effect of the lead.

Yes, an unvented cylinder will have safetey relive valves/overflows as will the boiler that need to be run to a safe location out side. The boiler being condensing will also require a condensate drain off which can be achived by various methods, depending on the location of your internal drains.

Theres no issue with using the loft as long as you are happy to access it to reset/fill boiler from time to time, and that it can adaquetly support the weight of a full Unvented cylinder (normaly 1kg per stored Litre of water + weight of empty cylinder (20-50kg))

The smaller boiler will allow less cycling as said, but be aware, underfloor heating is a slow heat over a long period so cycling is inevitable, boilers have setting to help reduce this but will be mostly ineffective when mixed with traditional heating radiators.

Combi as an option, Big gas pipe to get correct gas pressure to it in loft, as it will need to be a reasonable sized boiler to attain good hot water flow rates, it will still be fed through the lead pipe so will still need a certain pressure+Flowrate, however you really cant garuntee what it will do in terms of dynamic flow rate untill its on your system and you try it. Space saving yes, same issue with overflow and condensate, will cycle more on heating but not the end of the world.

 

[mark740]

Thanks for the reply mate much appreciated ,

I think the space is the most appealing to a combi by I understand thier limitations.... But didn't think about the larger gas supply.

So can you have the unvented cylinder in the loft then ? If so does that introduce any further issues ? Lagging etc.

Currently I have a cylinder under the stairs .....is it possible to put the unvented there and have the boiler in the loft ? I guess that would be a fair amount of pipework ?

I get you point on a system boiler and it being smaller so less cycling etc, my underfloor heating has its own blending manifold and pump but that's all, is there anything else I can do to improve the system when combining rads and underfloor ?

I am really pleased with the underfloor heating and it seems to work really well it actually seems to make the entire down stairs much warmer , I just want to.make sure I run it all as efficiently as I can .

Again.thanks for the reply its much appreciated

 

[ScottishGasMan]

There should be no issue fitting an unvented under the stairs so long as you can route the discharge pipe to outside safely.

They can go in a loft, but would require a large loft hatch and decent beams to take the weight (in an older house thats normally ok but unlikley on newer builds as the loft is for storage and not bearing as much weight)

Fitted correctly the pipes should be lagged regardless of where it is in the house, but definetly if its in loft.

As far as efficiency, the boiler alone will be a huge step up in efficiecny as opposed to a Back boiler, cycling is inevitable and with a mixed rad/UFH system there has to be a compromise, but essentially you will want to run the CH temp as low as you can for maximum efffect (but still warm enough to get useable heat from the rads) Over time you can replace rads with higher output ones which would allow lower flow temps increasing efficiency, but to buy new rads now for that purpose would not be cost effective, just when you do go to replace them try aim for bigger/more panels etc.

Big combis work well enough for good HW production, as said it will have the same limitation given to it by the lead pipe which may not even be noticable, but if a shower and tap are used, or both showers at the one time, theres a possibility it will affect the flow at one or both, but also the further away your combi is from the hot taps the longer your gonna need to run the water through to get it warm, cylinder under the stairs will possibly be closer to the most used features as opposed to combi in loft.

 

[mark740]

What is involved in the discharge pipework and is it required for.both a combi and unvented ( or just any unvented system ) ? For example can it be routed to the loft and out the gable wall? I say this is its an end of terrace and the stairs are on the party side slap bang in the middle of the house.

 

[ScottishGasMan]

If the boilers in the loft then you almost certainly will have to seal the system (if you go the combi route thats almost a definite) which means either way the boiler in the loft needs a discharge pipe, not a problem, stick it out the wall on the gable end with the boiler.

If you have an unvented cylinder it will have its own discharge, which can not be routed upwards, must fall through its route to out side, sometimes It can be discharged into household drains if the have been upgraded to suit high temperature discharge but currently yours almost certainly wont be,

 

[ScottishGasMan]

PS the other option is to keep a vented cylinder (can be upgraded to a high recovery for better heating efficiency) which will still be fed from the large storage tank in loft, your flow rate will essentially stay the same as it is just now to the taps, but no need for discharge from the cylinder

 

[bernardgreen]

The problem with putting a condensing boiler in the loft is you have to find a route the condensate drain to reach a suitable drain or soak away. If installed on the outside of the building and thus exposed to the elements then in winter freezing of the condensate will block the drain. The condensate sump in the boiler fills up and ( if fitted ) the safety float switch ( or similar ) operates and shuts down the boiler. If it is a boiler with no flood sensor fitted then the boiler floods internally while still burning and damage can occur.

 

[mark740]

What is a suitable drain ? can i go to the rainwater drain or does it need to go to the sewer ? I have a cast iron external soil pipe if that makes any difference ?

There is a chance that i could have it in a cupboard which will be build on the landing in place of the chimney breast once its removed but the cupboard would be 400mm deep is that, if a boiler says 330mm will that fit or does it require space around it etc ? ie can it fit tight into a space.

Are there any benefits to having an open vented system ? im not keen on having the header tanks in the loft tbh

 

[dilalio]

As every dwelling and existing system to get onto is different, your best bet is to get in two or three reputable "heating engineers" recommended by sources you trust.
See what they have to say and ask why.
Keep in mind you want an install that suits the property and not the one they prefer to fit - we all have one .
There will be pros and cons, nothing will be perfect!

Note: boiler in loft will also require safe access to boiler by engineer for future visits... Lighting, hand rail and boarded pathway and working area.
Condense pipe runs can be protected from freezing via various methods: trace heating/ lagging but obviously at a cost.

Get a good idea of your dynamic flow rate... Run kitchen cold tap whilst seeing how long it takes to fill a 2 litre jug from another mains source (washing machine hose or garden tap) and do calcs.
Example: 2L in 10 seconds = 12l/pm "whilst other mains is running". Remember this will drop when drawing mains in the loft!

As it happens, I am putting a new system in my own house as my old profile gave up the ghost after 25 years . I have 4bar static pressure and a dfr of 18l/pm.
My boiler will go in a cupboard in the garage conversion and all services are right there so it's "simples". I am going for an ATAG IC ECOMISER 35 (I like what I've read/heard/seen).

Good luck

 

[bernardgreen]

ie can it fit tight into a space.

Some boilers can , some can't, when choosing go on line or otherwise get a copy of the installation instruction as to how much space is really needed at the sides for access during servicing ( as oppsose to the comment "oh I can get it there OK ). Combination boilers, with more bits inside the boiler casing to service often need more access space than the same size system boiler where pumps and valves etc are not inside the boiler casing.

trace heating/ lagging but obviously at a cost.

Lagging only reduces the rate of heat loss. It cannot on its own prevent freezing, only delay it.

 

[Dean744PiN5]

A combi boiler would be a compromise, but if that's what you wanted to go for then the ATAG A325ECX with it's built in flue saver, that pre-heats the incoming mains by using the latent heat from the flue gases produced by the boiler would be a good choice. This gives a decreased temp rise from cold to hot (i.e the incoming main is warmer meaning the boiler doesn't need to work as hard to get up to it's set temp), increasing the boilers efficiency and giving higher flow rates, I have recorded up to 18lpm in the past.

Of course a combi is always a compromise and an unvented would most likely be better suited to your property, whoever quotes make sure that they take some actual flow and pressure readings down.

When it comes down to it, it will depend on your expectations of hot water performance, your actual pressure and flow and budget.

 

[mark740]

Well i have never had decent hot pressure anywhere i have lived, currently have a 1.5bar shower pump which while it gives a better shower than the electric ones i have had in the past its by no means powerful . the downstairs shower is gravity fed and is quite comparable to an electric but how this equates to any given slow rate im not sure.

Like you all have said this is going to depend on the flow rate via the old lead pipe i guess, when i had the extension done teh plumber who did the underfloor heating did use a flow cup and said it was perfect for a combi but i think he was just wanting to fit a combi.

What is the cheaper of the systems to use, i assume combi is the cheapest solely on there being less parts ( no cylinder etc ) and i assume less pipework, dont get me wrong i would rather spend more and get the right system but im just wondering.

another factor is going to be install time as i want the chimney brest removed (to create space) i will be without a boiler ( unless i can get the new one fitted first but id then be trusting a builder to removed the chimney and not damage the new install )

Dean where in Essex are you as im in Essex too

 

[Dean744PiN5]

@mark740 have sent you a pm Mark. I'm based in billericay but cover most of Essex.

 

[dilalio]

The new Atags have just been launched: IC ECONOMISER RANGE. I'm getting the 35kw model which gives 16l/pm @ 35 degrees. Promoted as the most efficient combi on the market.
Currently being supplied with free wifi controller which gives even better economy...
Before I sell it to you, read for yourself at Http://www.atagheating.co.uk