FAO PF Plumbers/Heating Engineers
17-12-2009, 02:42 PM
#1
...............
Thread Starter
FAO PF Plumbers/Heating Engineers
How do you work out if a combi boiler will comfortably heat my house and provide hot enough water?
Currently got a conventional boiler but it's old and inefficient so looking to replace it. Been quoted on a replacement Baxi combi and 17 TRV's plus a digital thermo.
What questions should I be asking about the boiler quoted?
Currently got a conventional boiler but it's old and inefficient so looking to replace it. Been quoted on a replacement Baxi combi and 17 TRV's plus a digital thermo.
What questions should I be asking about the boiler quoted?
17-12-2009, 02:54 PM
#2
How do you work out if a combi boiler will comfortably heat my house and provide hot enough water?
Currently got a conventional boiler but it's old and inefficient so looking to replace it. Been quoted on a replacement Baxi combi and 17 TRV's plus a digital thermo.
What questions should I be asking about the boiler quoted?
Currently got a conventional boiler but it's old and inefficient so looking to replace it. Been quoted on a replacement Baxi combi and 17 TRV's plus a digital thermo.
What questions should I be asking about the boiler quoted?
1, What Baxi combi are they quoting for?
2. How much guarantee are you getting?
3, Price?
4, Get at least 3 separate quotes!
17-12-2009, 05:45 PM
#4
Professional Waffler
17 rads, jees how bigs ya house? 
Well, it should be more than 17 rads, as you should really only fit about a third of the rads with TRV's if its a condensing boiler otherwise the high efficency of the boiler is out the window lol
Well, it should be more than 17 rads, as you should really only fit about a third of the rads with TRV's if its a condensing boiler otherwise the high efficency of the boiler is out the window lol
Last edited by Lee Reynolds; 17-12-2009 at 05:49 PM.
17-12-2009, 06:02 PM
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how many bathrooms u got? how many of u live there? if u got showers wat type r they?
u generally size a combi on hot water demand not heating. a combi is a 1 tap appliance if more hots than 1 are drawn at once a combi is not for u
if uve got 17 rads
17-12-2009, 06:05 PM
#6
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boiler scrappage scheme only applies to g rated boilers so u would need 2 check what rating ur boiler is! i dont know how it works if ur boiler is unrated tho
17-12-2009, 06:07 PM
#7
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i was wondering that about the trvs aswell, we always fit them to every one apart from where the room stat is. regs say you should atleast have them on the bedrooms though. With that many rads must be quite a big house, if i was fitting a new boiler in my house id go a megaflow and get lots of hot water pressure 
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17-12-2009, 06:27 PM
#8
PassionFord Post Whore!!
Problem with a combi is it does your hot water toooooo....
Basically - from my info from Tiff and also from the Mechanical Engineers at work ( I'm an Mechanical and Electrical QS - mechanical being plumbing- so these guys spec this stuff for a living and install it )
You need to work out what BTU's you need for each room.. a calculator like this will help.
http://www.theheatinglab.co.uk/btu_calc_guide.php
Alternativly you need to work out what output your radiators make- which may be more difficult, but if you take the length and height of your rads and how many panels you can compare them with currently available models and make allowance for them being older and less effcient maybe.
This may help http://www.mrcentralheating.com/radiators.html
Once you have a total BTU's required add about 20-25% to give you a total BTU output requirement for your boiler.
This isn't a fool proof plan but will give you a generally efficient system that can handle the amount of heat required.
You then need to look at hot water flow rate- I cant remember what the recomendation was but I know the 12.7 l/min I went for was again about 20% over what I needed for my application.
I would say though that 17 radiators PLUS domestic hot water supply does seem a lot for one Combi Boiler.
Basically - from my info from Tiff and also from the Mechanical Engineers at work ( I'm an Mechanical and Electrical QS - mechanical being plumbing- so these guys spec this stuff for a living and install it )
You need to work out what BTU's you need for each room.. a calculator like this will help.
http://www.theheatinglab.co.uk/btu_calc_guide.php
Alternativly you need to work out what output your radiators make- which may be more difficult, but if you take the length and height of your rads and how many panels you can compare them with currently available models and make allowance for them being older and less effcient maybe.
This may help http://www.mrcentralheating.com/radiators.html
Once you have a total BTU's required add about 20-25% to give you a total BTU output requirement for your boiler.
This isn't a fool proof plan but will give you a generally efficient system that can handle the amount of heat required.
You then need to look at hot water flow rate- I cant remember what the recomendation was but I know the 12.7 l/min I went for was again about 20% over what I needed for my application.
I would say though that 17 radiators PLUS domestic hot water supply does seem a lot for one Combi Boiler.
17-12-2009, 06:29 PM
#9
PassionFord Post Whore!!
PS
As above regarding TRV's but for safety you need to ensure that at least one radiator normally the bathroom doesn't have TRV's to ensure that if the flow gets shut off to every rad the water can still circulate or you may fuck the pump in the boiler... I am sure theres prob another techy solution to this, however both Tiff, the guys at work and MR Central Heating recomended this.
PPS - Mr Central Heating is about as cheap as you can get.
As above regarding TRV's but for safety you need to ensure that at least one radiator normally the bathroom doesn't have TRV's to ensure that if the flow gets shut off to every rad the water can still circulate or you may fuck the pump in the boiler... I am sure theres prob another techy solution to this, however both Tiff, the guys at work and MR Central Heating recomended this.
PPS - Mr Central Heating is about as cheap as you can get.
17-12-2009, 06:31 PM
#10
PassionFord Post Whore!!
PPPS you may find shortley that we as a country move away from Combi's due the water that is wasted while pulling through cold water that is stored in the pipes and heating it as it runs... pressurised water vessels give hot water instantly...
Have you considered a ground source heat pump???
Have you considered a ground source heat pump???
17-12-2009, 06:41 PM
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PS
As above regarding TRV's but for safety you need to ensure that at least one radiator normally the bathroom doesn't have TRV's to ensure that if the flow gets shut off to every rad the water can still circulate or you may fuck the pump in the boiler... I am sure theres prob another techy solution to this, however both Tiff, the guys at work and MR Central Heating recomended this.
PPS - Mr Central Heating is about as cheap as you can get.
As above regarding TRV's but for safety you need to ensure that at least one radiator normally the bathroom doesn't have TRV's to ensure that if the flow gets shut off to every rad the water can still circulate or you may fuck the pump in the boiler... I am sure theres prob another techy solution to this, however both Tiff, the guys at work and MR Central Heating recomended this.
PPS - Mr Central Heating is about as cheap as you can get.
17-12-2009, 06:53 PM
#12
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PPPS you may find shortley that we as a country move away from Combi's due the water that is wasted while pulling through cold water that is stored in the pipes and heating it as it runs... pressurised water vessels give hot water instantly...
Have you considered a ground source heat pump???
Have you considered a ground source heat pump???
u can get combis with a store so no heat up is required so less dead legs! as this gives the combi time 2 heat up before store is empty
a ground source heat pump is expensive to install, works best wiv underfloor heating as a larger heat transfer is needed as lower flow temp, roughly 40degrees! or massive rads can be used! also all the ground work required whether done by pile driving or snaking round a large area! a slightly cheaper alternative is air source heat pumps but jus not quite as efficient!
17-12-2009, 06:58 PM
#13
PassionFord Post Whore!!
pressurised water cylinders do NOT give hot water instantly i know this as i also have my tickets in un-vented hot water! no hot water cylinder gives hot water instantaniously only combi's, water heaters n thermal stores do. i fitted a unvented in my house and they r the bollox! high effiency (so heat up from cold in less than 15mins), high flow rate n high pressure no pumps required for showering!
u can get combis with a store so no heat up is required so less dead legs! as this gives the combi time 2 heat up before store is empty
a ground source heat pump is expensive to install, works best wiv underfloor heating as a larger heat transfer is needed as lower flow temp, roughly 40degrees! or massive rads can be used! also all the ground work required whether done by pile driving or snaking round a large area! a slightly cheaper alternative is air source heat pumps but jus not quite as efficient!
u can get combis with a store so no heat up is required so less dead legs! as this gives the combi time 2 heat up before store is empty
a ground source heat pump is expensive to install, works best wiv underfloor heating as a larger heat transfer is needed as lower flow temp, roughly 40degrees! or massive rads can be used! also all the ground work required whether done by pile driving or snaking round a large area! a slightly cheaper alternative is air source heat pumps but jus not quite as efficient!
I am just doing my dissertation on GSHP technology and their incorporation into existing housing stock.. YAWN!!!
17-12-2009, 07:02 PM
#14
pressurised water cylinders do NOT give hot water instantly i know this as i also have my tickets in un-vented hot water! no hot water cylinder gives hot water instantaniously only combi's, water heaters n thermal stores do. i fitted a unvented in my house and they r the bollox! high effiency (so heat up from cold in less than 15mins), high flow rate n high pressure no pumps required for showering!
u can get combis with a store so no heat up is required so less dead legs! as this gives the combi time 2 heat up before store is empty
a ground source heat pump is expensive to install, works best wiv underfloor heating as a larger heat transfer is needed as lower flow temp, roughly 40degrees! or massive rads can be used! also all the ground work required whether done by pile driving or snaking round a large area! a slightly cheaper alternative is air source heat pumps but jus not quite as efficient!
u can get combis with a store so no heat up is required so less dead legs! as this gives the combi time 2 heat up before store is empty
a ground source heat pump is expensive to install, works best wiv underfloor heating as a larger heat transfer is needed as lower flow temp, roughly 40degrees! or massive rads can be used! also all the ground work required whether done by pile driving or snaking round a large area! a slightly cheaper alternative is air source heat pumps but jus not quite as efficient!
Fitted a few of the unvented cylinders and all of my customers have been very impressed.
Looked into the ground source and air source heat pumps aswell, still a bit pricey just now for me. Another few years before it'll really take off i reckon.
Last edited by eddie_od; 17-12-2009 at 07:04 PM.
17-12-2009, 07:14 PM
#15
Professional Waffler
rodriguez concierto de aranjuez
You dont need to bang on about what papers you got mate.
Im going on tests shown that generally with a condensing boiler, fitting TRV's to all rads reduces the efficiency of the condense. Fitting it to a 3rd is supposed to be more efficient. Tests, and what my plumbers go by. Obviously, everyone has their own methods
You dont need to bang on about what papers you got mate.
Im going on tests shown that generally with a condensing boiler, fitting TRV's to all rads reduces the efficiency of the condense. Fitting it to a 3rd is supposed to be more efficient. Tests, and what my plumbers go by. Obviously, everyone has their own methods
17-12-2009, 07:32 PM
#16
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rodriguez concierto de aranjuez
You dont need to bang on about what papers you got mate. Im going on tests shown that generally with a condensing boiler, fitting TRV's to all rads reduces the efficiency of the condense. Fitting it to a 3rd is supposed to be more efficient. Tests, and what my plumbers go by. Obviously, everyone has their own methods
You dont need to bang on about what papers you got mate.
Im going on tests shown that generally with a condensing boiler, fitting TRV's to all rads reduces the efficiency of the condense. Fitting it to a 3rd is supposed to be more efficient. Tests, and what my plumbers go by. Obviously, everyone has their own methods
17-12-2009, 07:43 PM
#17
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yea they seem very impressive with figures bosting 400% efficiency for ground source heat pumps another is biomass dont know whether these will catch on! n obviously solar but england doesn't av the best climate but worth considering. aslo micro CHP's for domestic will be interesting to see if these get fitted!
17-12-2009, 07:58 PM
#18
Chasing Radders
Do we know how many bathrooms this guy has yet????????????
As if he has 1 bathroom and 17 rads then there are combi's on the market that will run that system...........be it fucking exspensive but there are ones out there such as the Valiant 937
As if he has 1 bathroom and 17 rads then there are combi's on the market that will run that system...........be it fucking exspensive but there are ones out there such as the Valiant 937
17-12-2009, 08:29 PM
#20
PassionFord Post Whore!!
Average 3 bed semi has 7 rads
3 beds
1 bathroom
1 kitchen
1 living room
1 hall way
My moms house (3bed semi- extended) has 9 and my house when the central heating is fitted will have 6 (2 bed semi)
3 beds
1 bathroom
1 kitchen
1 living room
1 hall way
My moms house (3bed semi- extended) has 9 and my house when the central heating is fitted will have 6 (2 bed semi)
17-12-2009, 09:41 PM
#21
Professional Waffler
im not banging on, so if this is true why do building regs state it is more efficient they obviously test every method! most condensing boilers modulate on a air gas ratio valve or zero governor n fan speed, to change the power output to keep the boiler condensing therefore increasing efficiency. granted the lower the return temp the better the efficiency the boiler cos an appropiate sized boiler will be needed to keep the boiler working hard to condense but the modulation improves this depending on required output. but also the harder the boiler works the qucker it will wear out so these maintenance costs should be taken into consideration
18-12-2009, 10:05 AM
#22
...............
Thread Starter
Just had a recount, its defo 17 rads! It's a large four bed detached. Two en-suites, 1 family bathroom and a downstairs bog so four bathrooms in total. It's a late 70's build and seems to be well insulated compared to my old place, a fifties bungalow which never warmed up even when the heating was flat out.
If I dont go for a combi, what is the difference in the running costs. I want to save money but dont want to compromise on heating and hot water, of which we have plenty at present.
If I dont go for a combi, what is the difference in the running costs. I want to save money but dont want to compromise on heating and hot water, of which we have plenty at present.
18-12-2009, 04:00 PM
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there r alternatives 2 a megaflo but they r defo the best, the santon is made by the same people (heatrae sadia) but is not a bubble top cylinder so come with an external expansion vessel
but also 2 remember any shower pumps or power showers will not be compatible with this system if already installed
18-12-2009, 05:20 PM
#26
Professional Waffler
Just had a recount, its defo 17 rads! It's a large four bed detached. Two en-suites, 1 family bathroom and a downstairs bog so four bathrooms in total. It's a late 70's build and seems to be well insulated compared to my old place, a fifties bungalow which never warmed up even when the heating was flat out.
If I dont go for a combi, what is the difference in the running costs. I want to save money but dont want to compromise on heating and hot water, of which we have plenty at present.
If I dont go for a combi, what is the difference in the running costs. I want to save money but dont want to compromise on heating and hot water, of which we have plenty at present.
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