Boiler requirements for a 5 bedroom, 5 bathroom house
Discussion
Evening.
I'm having a new house built and have had two very different opinions on the boiler requirement to sufficiently run the heating and hot water.
Gas engineer 1 says I will need 2 boilers and a cylinder in a dedicated plant room. One boiler to run 8 radiators underfloor heating, and two bathrooms, and a second boiler to run 12 radiators and three bathrooms.
Gas engineer 2 said a large combi or system boiler with a cylinder would be enough for the entire house.
I had a new 25mm water main put in, and the plumber has already installed a 22mm pipe the length of the house with 22mm runs to the rads, switching to 15mm no more than 500mm from each rad.
2 parents and 2 kids so realistically 3 showers at any one time, possibly 4 maximum. Not really fussed about zoning the upstairs and downstairs rads.
I get that different engineers will have different preferences, but it seems they're at each end of the spectrum.
Does anyone have similar setups, or any tips/pitfalls to avoid?
TIA
I'm having a new house built and have had two very different opinions on the boiler requirement to sufficiently run the heating and hot water.
Gas engineer 1 says I will need 2 boilers and a cylinder in a dedicated plant room. One boiler to run 8 radiators underfloor heating, and two bathrooms, and a second boiler to run 12 radiators and three bathrooms.
Gas engineer 2 said a large combi or system boiler with a cylinder would be enough for the entire house.
I had a new 25mm water main put in, and the plumber has already installed a 22mm pipe the length of the house with 22mm runs to the rads, switching to 15mm no more than 500mm from each rad.
2 parents and 2 kids so realistically 3 showers at any one time, possibly 4 maximum. Not really fussed about zoning the upstairs and downstairs rads.
I get that different engineers will have different preferences, but it seems they're at each end of the spectrum.
Does anyone have similar setups, or any tips/pitfalls to avoid?
TIA
I would go with option 1 if space and finnances allow
2 smaller boilers are going to be under alot less stress and cheaper to run than a big beast to power everything on its own.
Make sure the hot water tank has an emmersion heater as a redundancy. Just in case the heating goes.
I would also make the shower in the spare bedroom an electric shower so if your hot water goes you can still have a shower.
2 smaller boilers are going to be under alot less stress and cheaper to run than a big beast to power everything on its own.
Make sure the hot water tank has an emmersion heater as a redundancy. Just in case the heating goes.
I would also make the shower in the spare bedroom an electric shower so if your hot water goes you can still have a shower.
To do it right, more info is required..
Where is the house? Up a mountain in Northern Scotland or on the South Coast neat Torquay?
What s the floor area? What ceiling heights? Double or triple glazing? What insulation has been used? To code or way above? What distances from one end of the house to another?
Just supplying bedroom and bathroom numbers without context isn t going to design the right system for the house.
It all depends on the individual project - what works in one place might not be as good in another 5bed, 5bath property.
Ask both why their approach is better than what the other has suggested - that should be telling.
Where is the house? Up a mountain in Northern Scotland or on the South Coast neat Torquay?
What s the floor area? What ceiling heights? Double or triple glazing? What insulation has been used? To code or way above? What distances from one end of the house to another?
Just supplying bedroom and bathroom numbers without context isn t going to design the right system for the house.
It all depends on the individual project - what works in one place might not be as good in another 5bed, 5bath property.
Ask both why their approach is better than what the other has suggested - that should be telling.
Edited by dobly on Monday 12th January 20:51
I am absolutely not saying that this is the way to go, but we run a 3000 sq ft, 200 year old house with five beds and three baths off a 28kw combi with 20 rads. It’s absolutely fine and even runs two showers at once.
I am by no means an expert, but 3000 sq ft isn’t a big house, so a single system boiler and big cylinder sounds more than adequate.
I am by no means an expert, but 3000 sq ft isn’t a big house, so a single system boiler and big cylinder sounds more than adequate.
Crumpet said:
I am absolutely not saying that this is the way to go, but we run a 3000 sq ft, 200 year old house with five beds and three baths off a 28kw combi with 20 rads. It s absolutely fine and even runs two showers at once.
I am by no means an expert, but 3000 sq ft isn t a big house, so a single system boiler and big cylinder sounds more than adequate.
The house size was mine rather then the OPs, but sounds similar on the beds/baths so shared my experience. I am by no means an expert, but 3000 sq ft isn t a big house, so a single system boiler and big cylinder sounds more than adequate.
Crumpet said:
I am absolutely not saying that this is the way to go, but we run a 3000 sq ft, 200 year old house with five beds and three baths off a 28kw combi with 20 rads. It s absolutely fine and even runs two showers at once.
I am by no means an expert, but 3000 sq ft isn t a big house, so a single system boiler and big cylinder sounds more than adequate.
Half the size but 11 rads on 28kw combi which was fitted when we were 2 beds now 4 we thought it may struggle but been fine for a decade. Only just runs 2 showers though.I am by no means an expert, but 3000 sq ft isn t a big house, so a single system boiler and big cylinder sounds more than adequate.
If it is a new build ( assuming you are on the uk ) then it will be built to the new regs that came in about 2 years ago.
We have a large house completed in 2023 to the old regs.
It simply does not get cold. The whole house is heated by the hall / kitchen / my office that is it. It is 3 floors. The house is about 21 degrees all over.
We have under floor heating. We have one boiler.
Your contractor will have to have sap calculations to pass regs a that will give energy requirement.
It won't be much.
We have a large house completed in 2023 to the old regs.
It simply does not get cold. The whole house is heated by the hall / kitchen / my office that is it. It is 3 floors. The house is about 21 degrees all over.
We have under floor heating. We have one boiler.
Your contractor will have to have sap calculations to pass regs a that will give energy requirement.
It won't be much.
A house that size to latest regulations does not require two boilers.... 
I've got a similar size place, with less insulation and a very inefficient design, and an 8kw ASHP that works perfectly well, & even during cold spells only runs part time.
No idea what the equivalent is for gas boiler, but it won't be overly big.... 30kw ish, at a guess?! Then get a 300L cylinder, that'd do 4 easy showers, 2 running at the same time.
I don't see how your water pressure can run 3 showers at the same time, let alone boilers to keep up?
I've got a similar size place, with less insulation and a very inefficient design, and an 8kw ASHP that works perfectly well, & even during cold spells only runs part time.
No idea what the equivalent is for gas boiler, but it won't be overly big.... 30kw ish, at a guess?! Then get a 300L cylinder, that'd do 4 easy showers, 2 running at the same time.
I don't see how your water pressure can run 3 showers at the same time, let alone boilers to keep up?
Edited by Andeh1 on Monday 12th January 21:46
Returningmember said:
Evening.
I'm having a new house built and have had two very different opinions on the boiler requirement to sufficiently run the heating and hot water.
Gas engineer 1 says I will need 2 boilers and a cylinder in a dedicated plant room. One boiler to run 8 radiators underfloor heating, and two bathrooms, and a second boiler to run 12 radiators and three bathrooms.
Gas engineer 2 said a large combi or system boiler with a cylinder would be enough for the entire house.
I had a new 25mm water main put in, and the plumber has already installed a 22mm pipe the length of the house with 22mm runs to the rads, switching to 15mm no more than 500mm from each rad.
2 parents and 2 kids so realistically 3 showers at any one time, possibly 4 maximum. Not really fussed about zoning the upstairs and downstairs rads.
I get that different engineers will have different preferences, but it seems they're at each end of the spectrum.
Does anyone have similar setups, or any tips/pitfalls to avoid?
TIA
The second plumber appears to use less gack at breakfast. I'm having a new house built and have had two very different opinions on the boiler requirement to sufficiently run the heating and hot water.
Gas engineer 1 says I will need 2 boilers and a cylinder in a dedicated plant room. One boiler to run 8 radiators underfloor heating, and two bathrooms, and a second boiler to run 12 radiators and three bathrooms.
Gas engineer 2 said a large combi or system boiler with a cylinder would be enough for the entire house.
I had a new 25mm water main put in, and the plumber has already installed a 22mm pipe the length of the house with 22mm runs to the rads, switching to 15mm no more than 500mm from each rad.
2 parents and 2 kids so realistically 3 showers at any one time, possibly 4 maximum. Not really fussed about zoning the upstairs and downstairs rads.
I get that different engineers will have different preferences, but it seems they're at each end of the spectrum.
Does anyone have similar setups, or any tips/pitfalls to avoid?
TIA
Current house is a leaky old, single glazed 2500 with 15 or so rads. It runs perfectly well on a boggo combi. Previous one was leaky, 5000 sqft with 30 or so rads and just used a normal boiler and a mega flow tank.
A 30kW or 36kW boiler on its own should be plenty. If you really want to run 3 showers at once then you absolutely need a HW cylinder and an accumulator in front of that. As a new build you might want to consider solar thermal heating for the tank(s) as well.
There’s no way you need 2 boilers for that. It adds more complexity to the system than you might think and you would usually have bigger primaries even than the 22mm pipes you have.
There’s no way you need 2 boilers for that. It adds more complexity to the system than you might think and you would usually have bigger primaries even than the 22mm pipes you have.
I’d have wet underfloor heating as a preference to rads, at least on the ground floor, for starters.
More wall space for flexibility, & a comfortable experience (purely based on our sun room extension we had done a decade ago).
A single boiler should be fine: ours is a system boiler, which makes for a decent power shower. Currently feeds 19 rads and wet UFH in a 40m2 sunroom.
That said, if all 3 showers were in use at once, pressure might drop a bit…..& the idea of an electric spare is a good one.
ASHP? Perhaps, with a decent battery system to backup (& obvs solar). No personal experience, although with a modern well insulated house, it could work….although my only experience with electric UFH was some we retrofitted which was HUGELY expensive
More wall space for flexibility, & a comfortable experience (purely based on our sun room extension we had done a decade ago).
A single boiler should be fine: ours is a system boiler, which makes for a decent power shower. Currently feeds 19 rads and wet UFH in a 40m2 sunroom.
That said, if all 3 showers were in use at once, pressure might drop a bit…..& the idea of an electric spare is a good one.
ASHP? Perhaps, with a decent battery system to backup (& obvs solar). No personal experience, although with a modern well insulated house, it could work….although my only experience with electric UFH was some we retrofitted which was HUGELY expensive
4500sqft house (over 4 1/2 floor), 25 radiators, 4 bathrooms.
1 boiler and 1 cylinder. No issues.
There is definitely no need for OP to be installing 2 boilers, although if space and finances suit then it’s certainly something worth considering as will mean the equipment is less stressed and in the event of a boiler failure you’ll have a backup.
1 boiler and 1 cylinder. No issues.
There is definitely no need for OP to be installing 2 boilers, although if space and finances suit then it’s certainly something worth considering as will mean the equipment is less stressed and in the event of a boiler failure you’ll have a backup.
Over 5,000 sq ft here, very old house with 5 bathrooms all off one oil boiler and a single hot water cylinder. Currently getting a heat loss survey done and early indications are that the boiler (70kW) is way oversized.
In my experience gas/oil engineers don't do maths, they just oversize and over complicate stuff to make sure they never undersize, without knowing what is actually needed.
For a new build I'd definitely be going ASHP.
In my experience gas/oil engineers don't do maths, they just oversize and over complicate stuff to make sure they never undersize, without knowing what is actually needed.
For a new build I'd definitely be going ASHP.
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