New Boiler Needed... Does Size and Makers matter?

[gingapete]

Good afternoon,

I have finally saved some money to look at replacing my boiler (I have a limping wounded Heatline Capriz28 which needs to be gracefully retired after 7 years service) and need to look at what size i need so i can check the models available, review them and see what deals are around and about!

So i did a boiler size on my 3 bed semi (see below) with now added extension (knock through kitchen/dinner, utility and downstairs shower room so taking that in to account) and it comes back as boiler out put 26.8kW so anything around 28/30kW would be good as i am fitting mains showers in both bathroom and shower room?

Whole House Boiler Sizing Method - Results
Job Reference: 25 March 2013 13:32

Area Calculation
Length (m) 13.0
Width (m) 9.0
Height (m) 4.0
No. of floors 2
No. of walls width-wise 2.0
No. of walls length-wise 1.0
Calculated wall area (sq m) 248.0
Wall and Window Heat Losses
Dwelling type Semi-detached
Window area 49.6
Window type Double glazed wood/plastic
Window heat loss (W/deg) 148.8
Wall type Filled cavity wall
Wall heat loss (W/deg) 89.2
Roof and Floor Heat Losses
Roof area 117.0
Floor area 117.0
Roof insulation Pitched < 50mm insulation
Roof heat loss (W/deg) 304.2
Floor heat loss (W/deg) 81.8
Fabric Loss
Wall+window+roof+floor heat loss (W/deg) 624.1
Location North & Midlands
Calculated fabric heat loss (W) 18101
Ventilation Loss
Calculated volume (m3) 936.0
Location factor 29.0
Ventilation heat loss (W) 6786
Calculate Boiler Output
Calculated total heat loss(W) 24887
Add for water heating (W) 2000
Add for extension or other (W) 0
BOILER OUTPUT (kW) 26.8

I've read that putting in a larger than needed boiler not only costs more but would be dearer to run is this right?

I've been quoted a Valiant EcoTech Pro 28 with flue for just under £700 which i think is pretty good value and think would be fine but would i be best getting the next one up in case i convert the attic?

Cheers
Pete

 

[Phill Peck]

When you say mains showers do you mean electric or running of the combi.

The kw rating of a combi does not nessisarilly mean it has that output to heating. Also the boiler can be range rated to suit the load

 

[gingapete]

When you say mains showers do you mean electric or running of the combi.

The kw rating of a combi does not nessisarilly mean it has that output to heating. Also the boiler can be range rated to suit the load

Showers will be mains. Sorry if this is a thick question, but what does range rated mean?

 

[D_Hailsham]

Height (m) 4.0

So your floor to ceiling height is nearly 13ft???

 

[gingapete]

Height (m) 4.0

So your floor to ceiling height is nearly 13ft???

Hahaa, nope got that one wrong there, i hit a 4 instead of 3. Most downstairs is 3 upstairs is 2.5ish

 

[Agile]

Most standard British semis, even with solid walls only need 10-12kW so I dont k now why you need twice as much heat as anyone else!

Correcting the loft insulation thickness will help though.

Combi boilers are sized on their water outputs which are always more than the heat needed.

 

[gingapete]

Did a redoo on the calcs changing the ceiling height and the loft insulation as it's more than i thought and the result was "The required boiler output is 15.95 kW"

 

[mogget]

Did a redoo on the calcs changing the ceiling height and the loft insulation as it's more than i thought and the result was "The required boiler output is 15.95 kW"

Sounds more like it.

 

[gingapete]

When you say mains showers do you mean electric or running of the combi.

The kw rating of a combi does not nessisarilly mean it has that output to heating. Also the boiler can be range rated to suit the load

Sorry i meant to say running off combi not just repeat mains again!

 

[gingapete]

Did a redoo on the calcs changing the ceiling height and the loft insulation as it's more than i thought and the result was "The required boiler output is 15.95 kW"

Sounds more like it.

Soooooooo with that in mind, the 28 i got quoted would be good enough?

 

[Phill Peck]

If you are planning to run 2 showers you should be considering a storage combi eg Vaillant 937 or a heat only boiler and cylinder (unvented or not)

Have yo checked your incoming mains flow rate and pressures (static and dynamic)

You could find a combi boiler is not not suitable for you.

By the sounds of your post you are planning on staying in this house for a while?(loft extension)
If this is the case don't scrimp on the install. I would defiantly go with an unvented cylinder in a property with 2 or more showers

 

[mogget]

Yes but bear in mind there is a minimum rate that the boiler will supply. If your TRV's have closed you may end up with the boiler short cycling which isn't much good. That said, if you are going for a combi it will be sized for hot water demand and will nearly always be oversized for heating demand. You will have trouble running two showers off a combi.

 

[gingapete]

If you are planning to run 2 showers you should be considering a storage combi eg Vaillant 937 or a heat only boiler and cylinder (unvented or not)

Have yo checked your incoming mains flow rate and pressures (static and dynamic)

You could find a combi boiler is not not suitable for you.

By the sounds of your post you are planning on staying in this house for a while?(loft extension)
If this is the case don't scrimp on the install. I would defiantly go with an unvented cylinder in a property with 2 or more showers

Two showers, sorry misinformation again there, Im not planning on running them the same time i was just adding that there would be two in the house. At the moment i can get hot water to the bath but when running hot water downstairs at the same time the bath slows right down with old boiler. So were used to not running two things at once.

Not checked mains flow rate or pressures. Get ready for thicko question, flow rate and pressures testing? How?

Yeah staying for a while, but loft is a few years away from where i am now.

 

[Phill Peck]

Flow rate can be calculated using a bucket but ideally a weir gauge

Time how long it takes to fill a bucket say 10ltrs. If it takes 30 seconds your flow rate is 20 litres a min-not bad
If its 10 litres a minute not great

For pressure you will need a pressure gauge that can attach to outside tap or similar

These test can be done by a heating engineer who is quoting for the job and then recommending a product.
I can understand you wanting to do your research but it is bes to get the advice of a professional which can only be done accurately by doing a survey.

If you are happy that only outlet can run at once and are used to working his way then the 28 pro would be fine.
It can be range rated down which means it will give @28kw to heat the hot water but can be adjusted from @7-24 kw for heating(roughly I can't Romberg exactly)

 

[gingapete]

Flow rate can be calculated using a bucket but ideally a weir gauge

Time how long it takes to fill a bucket say 10ltrs. If it takes 30 seconds your flow rate is 20 litres a min-not bad
If its 10 litres a minute not great

For pressure you will need a pressure gauge that can attach to outside tap or similar

These test can be done by a heating engineer who is quoting for the job and then recommending a product.
I can understand you wanting to do your research but it is bes to get the advice of a professional which can only be done accurately by doing a survey.

If you are happy that only outlet can run at once and are used to working his way then the 28 pro would be fine.
It can be range rated down which means it will give @28kw to heat the hot water but can be adjusted from @7-24 kw for heating(roughly I can't Romberg exactly)

Thanks for that i know what you mean now! I will try the bucket test and see what comes out. And now i understand what range rated means!! Sometimes asking the questions that you think are stupid or make you look stupid get you exactly what you need! Cheers Gass!

Yeah we are used to the way we have it at the mo i am looking to future proof it a little as got a lil one on the way and that will mean more heating and deffo more hot water for baths and washing so im lead to believe!!