Less heat in a condensing boiler

[Gerard17]

Did any1 no that a a normal gas boiler heats a rad 30% more than on a condensing boiler. Has any1 ever fitted a new boiler like a combi swap an the customer says the house isn't has hot?

 

[Billy Bob Bob]

Did any1 no that a a normal gas boiler heats a rad 30% more than on a condensing boiler. Has any1 ever fitted a new boiler like a combi swap an the customer says the house isn't has hot?

no,never have had that issue

 

[kozak1968]

Turn boiler stat up if they complain.

 

[SJB6]

A properly sized boiler means that should never happened.

 

[Gerard17]

I've had it once or twice but just think there being silly as there not complaining or anything but when I went on that worcester course 1 of the worcester fellas (who knew his stuff) was telling me about the diffrence between them. I couldn't work it out as the water in the rad can still get up to 80 degrees if u wanted it to

 

[Gerard17]

Properly sized boiler??? 30si in a 2 bed, 1 bath, 6 rad system don't no what calculations u do but I would say that was more that adequate

 

[Roger Welton]

With the lower flow temps the cond boilers like to run with the output of the radiators does drop, though as mentioned above, turn up boiler stat to max and it'll be fine, not condensing but belting the heat out.

 

[vern]

As long as the return stays below 55 degs it will condense!

i think the OP is getting mixed up when the rads manufactures changed the delta t calcs, from 60 to 50

 

[Gerard17]

So if the return is above 50 degrees the boiler doesn't condense

 

[Roger Welton]

Dew point of water is aprox 55deg

 

[Gerard17]

I new that

 

[vern]

So if the return is above 50 degrees the boiler doesn't condense

Correct 55 not 50 ....hence on WB,Vaillants etc, max flow is 75 degs ( unless you override it) balance to get your 20 deg diff, return stays at 55 degs so boiler stays in condensing mode, until SYTEM cannot dissipate any more heat evenafter modulating down, then diff drops, return temp goes up, boiler stops condensing...

 

[Bronze_tap]

A properly sized boiler AND RADIATORS means that should never happened.

The properly tuned condensing boiler STARTS condensing at ~55 degrees or so,
Than, the LOWER the return T the MORE% of the H2O vapor it condenses (an the more fuel(money)% it can save).
To get MOST of it, DOUBLING radiator size/output is strongly recommended.
(versus typical old system). + room thermostat.
Usually it is mentioned somewhere in small print in the boiler install manual, (like for Junkers).
There is really very little gain from the condensing boiler on a tiny piping hot radiatos... (Unless you blow a fan on each of them (like on the PC's CPU cooler))

And the usually way undersized radiators of the typical UK installation are rarely mentioned... (Unlike the boiler size).

I've lived in 10 houses for the last ~10 years, and only the St. John's college had a properly sized radiators for the condensing boiler...

PS: I would not be surprized if the UK government adds a regulation in a future (in a bit to get higher energy efficiency/insulation), that the house should reach at least 18 degrees, when the outside temp is 0, and the maximum flow temp is 40-45 degrees (return 30-25 degrees). I've seen few houses with the 100+ years old systems perfectkly functioning (and crast iron/bronze radiators), which were meeting this flow temperature requirements.

 

[Howsie]

Hurt my head reading that.