22mm or 28mm from Gas meter to New boiler

[GeddyMortgage]

Hi all,

Trying to verify ive been given the correct info here (oppose to what's convenient for the installer)

Having a new boiler 36kw system boiler installed which will be 3-4M or so away from the gas meter, with id say about as many 45/90degree turns in it. (3-4). Installer has suggested fine to use 22mm flexible tracpipe (as it will be mostly buried). Which I guess sounded fine but given the size of the boiler and number of turns in the pipe I was surprised he didn't suggest 28mm.

What do you guys think? Worth going for 28mm despite the slight increase in cost?

Note: there are other appliances in the property such as fire, gas cooker, another boiler etc.... but they're each on their own direct feeds to the meter.


thanks

Geddy

 

[Deleted member 267285]

It would need to be sized correctly, not just guesstimated. I have no dealings with tracpipe, but think it comes in a coil, so bends should be at a minimum imo.

 

[fixitflav]

On the Tracpipe website there's an on-line calculator, so you can check it yourself. As a start, I make gas flow 3.6 m3/h.

Must be a big house if it needs a 36kW system boiler!

 

[ianmcd]

36KW ststem boiler ? do you live in a castle ?

 

[GeddyMortgage]

On the Tracpipe website there's an on-line calculator, so you can check it yourself. As a start, I make gas flow 3.6 m3/h.

Must be a big house if it needs a 36kW system boiler!

very helpful thanks, i'll check it out. To be fair the guy that came round is a gas engineer but as i've had so many dealings over the past few years with folks that 'talk' a big game... i think it's always good practice to double check this stuff now a days.

It's on the larger side yeah, had a difficult winter so deciding to upgrade the CH a bit. Believe it or not this new 36kw will only serve the ground floor, there's already a boiler with unvented tank up on the top floor that will continue to do hot water and the CH for the top 2 floors, the 36kw system was at the recommendation of the engineer. Ive assumed he's done the heat loss calcs.... but now i think about it i haven't seen them.

ground floor will have 14 rads or so, all double panel convector type 22 or triple column designer types. Is 36kw excessive do you think?

 

[GeddyMortgage]

36KW ststem boiler ? do you live in a castle ?

Fortunately not, it has a cavity and CWI . But the current boiler ain't quite able to heat the entire house efficiently. So zoning it that off just to cater for the top 2 floors, and adding this new one for the ground floor (ground floor will have 14rads, all either double panel or triple column type)

Do you think it's excessive at 36kw? i'm only going off what the Engineer has recommended here.

 

[Deleted member 281264]

36kw would be fine for a humungous uninsulated house

you say yours has good insulation, so seems insanse to not have a proper heat loss calc.

 

[fixitflav]

Fortunately not, it has a cavity and CWI . But the current boiler ain't quite able to heat the entire house efficiently. So zoning it that off just to cater for the top 2 floors, and adding this new one for the ground floor (ground floor will have 14rads, all either double panel or triple column type)

Do you think it's excessive at 36kw? i'm only going off what the Engineer has recommended here.

There are on-line heatloss calculators. I'd be surprised if they come up with anywhere near 36kW. What's the existing boiler output?

 

[Madrab]

If there are other appliances on the same meter then it depends on their requirements too and what size of pipe and meter you have feeding all those appliances. As long as he has done the proper calcs and the pipes are sized accordingly. It needs to be looked at in the whole as far as pipe sizes to the other appliance are concerned too etc.

As far as the rads and boiler output is concerned then a 36Kw is pretty big - To give you an example - you would need to have 14 - 600mmx1100mm Type 22 rads to look at max'ing out a 28Kw boiler never mind a 36kw.

Easy enough to work out though, perform the heat loss calcs as suggested above - then spec the rads to cover that heat loss, then take the rads and total up their output, that will give a starting figure of the boiler size required to satisfy them. BTW, column rads look lovely but the way they heat large spaces isn't very good, hence they really need to be oversized.

 

[GeddyMortgage]

36kw would be fine for a humungous uninsulated house

you say yours has good insulation, so seems insanse to not have a proper heat loss calc.

He is doing a heat loss calc. I said its got CWI, i wouldnt go so far to say its really well insulated. Loft was done by me over the winter. Still need to finish off the sub floor insulation (it's a 1950's house)

 

[GeddyMortgage]

There are on-line heatloss calculators. I'd be surprised if they come up with anywhere near 36kW. What's the existing boiler output?

you'll laugh, but the current boiler up in the loft is a 40kw conventional boiler with unvented cylinder. It was powering 24 rads (10 x type 11, 14 x type 22) and struggling quite a bit over the winter to keep the house super warm. Plus costing us an absolute fortune to run....plus plus, as we've just done an extension we'd be adding 3 more rads in so will be 27rads in total....

poor insulation (now rectified) obviously played a part here, but also when I went down the sub floor to have a look at everything.... I saw that when the flow and return from the loft boiler get to the ground floor (22mm) they both immediately go down to 10mm and feed every one of the 14 radiators on that floor. Spanning a good 25meters or so in total. And to be entirely honest, the quotes I got for replacing all that to 22mm wasn't hugely cheaper than just adding a second boiler for the ground floor, and capping off those 22mm flow and returns which then in turn will make the original boiler only power the top 2 floors. Also worth mentioning as that now will only be powering 10rads and the cylinder, we will likely swap it down from a 40 to a 28kw when it inevitably dies.

 

[GeddyMortgage]

If there are other appliances on the same meter then it depends on their requirements too and what size of pipe and meter you have feeding all those appliances. As long as he has done the proper calcs and the pipes are sized accordingly. It needs to be looked at in the whole as far as pipe sizes to the other appliance are concerned too etc.

As far as the rads and boiler output is concerned then a 36Kw is pretty big - To give you an example - you would need to have 14 - 600mmx1100mm Type 22 rads to look at max'ing out a 28Kw boiler never mind a 36kw.

Easy enough to work out though, perform the heat loss calcs as suggested above - then spec the rads to cover that heat loss, then take the rads and total up their output, that will give a starting figure of the boiler size required to satisfy them. BTW, column rads look lovely but the way they heat large spaces isn't very good, hence they really need to be oversized.

Very interesting read thanks. Coincedentally it will be running 14 rads of similar size to that. Most will be type 22, some will be the designer type triple column, cannot recall if their BTU requirements were higher or lower than the type 22's.

Though the engineer did say oversizing is better than under sizing and that the boiler will modulate down should it's demand be significantly less than capacity.

I'll try one of the calcs myself to see I guess... Modern day standards should be based on T50 or T40 when working out the delta/BTU etc?

 

[fixitflav]

very helpful thanks, i'll check it out. To be fair the guy that came round is a gas engineer but as i've had so many dealings over the past few years with folks that 'talk' a big game... i think it's always good practice to double check this stuff now a days.

It's on the larger side yeah, had a difficult winter so deciding to upgrade the CH a bit. Believe it or not this new 36kw will only serve the ground floor, there's already a boiler with unvented tank up on the top floor that will continue to do hot water and the CH for the top 2 floors, the 36kw system was at the recommendation of the engineer. Ive assumed he's done the heat loss calcs.... but now i think about it i haven't seen them.

ground floor will have 14 rads or so, all double panel convector type 22 or triple column designer types. Is 36kw excessive do you think?

Sounds like the house is a lot bigger than average, so possible 35 kW needed. Still worth doing a proper check though.
On your original question about pipe size, from the Tracpipe calculator, 5m of 22 mm pipe looks fine for pressure drop. But I think you ought to do it yourself, or get the engineer to do it.

 

[GeddyMortgage]

Sounds like the house is a lot bigger than average, so possible 35 kW needed. Still worth doing a proper check though.
On your original question about pipe size, from the Tracpipe calculator, 5m of 22 mm pipe looks fine for pressure drop. But I think you ought to do it yourself, or get the engineer to do it.

It's got an awkwardly large footprint to be fair yes. Was originally a 1950's bungalow but extended upwards a couple times.

As it had so many rads in total due to the above, it was either go for a commercial size boiler, or have multiple boilers which i've obviously opted for the latter, essentially treating the ground floor as a bungalow as it used to be...

I did a basic run over of one of the online heat loss calcs earlier and the wattage did come out less than i thought...to the point where I feel the calculator was being wayyyy too generous. E.g our 'Lounge' is 6m by 4.5m, baywindow 3.6m wide, 2m tall. Suspended floor below it.... the calculator said for that room i'll only need 2200 watts to heat appropriately @ T50? Based on what im looking at online.... that'd be one type 22 radiator of reasonable size.... that seems far too small.

Super simply in my head i'd done it like this (before I did the online calculator) ...If large room (like the lounge above) = 2 x type 22 rads (5k wattage-ish?)... if very large room 3x type 22 rads (7.5k wattage-ish?)

14 type 22 rads @ 2.5kish = 35kw... though ofcourse i appreciate that's over-simplified.

 

[Deleted member 281264]

I highly doubt any extended bungalow needs a 35kw boiler. A proper heat loss calc will probably tell you you need 20kw maximum.

Get a Viessmann 200W. It modulates down 1:19, then if you oversize it it wont matter as much.