Trying to Compare Plumber quotes??

I am trying to compare plumber quotes for a 3500 sq ft house in Kildare which are ranging from 18k to 31K!!! and I can't figure out where the differences are. Can someone please give me some guidance as to where the major differences might be?

I got all 5 plumbers to come around the house with me and explained that I wanted the following system:

Oil Condensing Boiler in external garage
30m Insulated pipe from garage to house
Oil Tank
Flue from Garage for Boiler
Approx 25 thermostatically controlled rads (specified type) and piping and a kick space heater
Heating to be split into 5 zones
1 No. Insulated copper cylinder fitted in hp
1 No Storage tank and pressure pump (type specified) fitted in garage to feed all hot and cold services and pressurised to 1.5 bar
Fitting of all sanitary ware including 2 ensuites, 2 bathrooms and 1 wc
Leaving provisions for 2 no sinks, dishwasher and washing machine
Finsihing all soils and wastes into finished builders pipes/gulleys
All copper and necessary fittings supplied to fit the above

I have been warned again and again that the cheapest plumbers quotes are not always the best but what questions can I ask to try and fish out the cowboys from the robbers???

Advice would be apprecaited?

Get each of them to supply you with a written quote detailing all that you set out above and make sure they are quoting for labour and materials and ancillary works that may be involved. When you get those quotes compare them then, pick whichever is the most comprehensive one (disregard the price for a minute) and get the others to quote for exactly the same. Play them off one another and when you're happy with a quote go with it but try to get some form of contract to avoid hassle further on. For that much money it would be vital IMO. If they're unwilling to do that for you, walk away from them.

Have you specified what make/model/ of boiler you want?

Have plumbers specified what boiler they will use, make/model/output?

Do you want your home to be piped with no fittings in unaccessible places I.E under floors etc?

This would be achieved by running separate lines to eveything(sinks,radiators etc) and bringing them back to a centre manifold. 1 or two manifolds for plumbing and a manifold for each heating zone.

This is more costly (more labour/material used) than having a main line(every zone having its own main line) with tee's off it. but you are nearly 100% sure of no leaks under floors for the properties life time.

You should ask them to specify what electrical parts they plan to use e.g circulation pumps and motorised/zone valves on heating. Prices vary greatly depending on quality.

How many pumps will heating system have?

What size cylinder?

Will cylinder have stat?

What make are TRV's?

Will bathroom radiators/towel warmers be piped into primary circuit? I.E When hot water only is on (summer time), bathroom heat source is on?

How many runs in insulated pipe from boiler to house?
You want the incased pre-insulated ducted pipe. It is expensive but worth every penny in the long run.

thanks for those pointers folks...had compared sizes of cylinders, boilers, no of rads etc but one thing you have highlighted there is the manifolds and having no connections under the floors...will check that out as one of the pricer quotes definately has allowed for this...

I presume having no connections under the floor is the more sensible route to take - anyone have any opinions on this???

What are trv's?? (probably a stupid question)

Davey Jones what do you mean by the following - "How many runs in insulated pipe from boiler to house?"

Cheers for your help

Also bear in mind the most expensive is not necessarily the best either. We got some work done & the guy was not cheap.....but was a cowboy! had to sack him in the end, but we still have on going problems with the work he did.

References are probably your best - find other new builds (actually, probably best to look for 1 or 2 year old houses as they will have ironed out any problems they had) in the area and ask them for references.

all the plumbers that we got to quote were referred by someone that has completed a new build in the last 4 years...and they all gave them the thumbs up....

can anyone answer the few questions I raised in my last reply???

Thermostatic radiator valves

Ducted insluted pipe comes with two pipes in one pipe. Will there be only 1 main heating line entering house and then split or will there be more than 1 main line?

Advantages of manifold system
100% leak free underfloor, unless someone puts a nail/screw into pipe.
all connections above ground.

Disadvantages
More expensive
Running cost may be slightly higher as there is more water to heat in system, however this is debatable. It would depend on control over system.