Combi for 3 bed semi

kev1234

Bit of a novice but have a few queries on combi gas boilers. We are currently completing extension and refurbishment works on our 3 bed semi in Dublin. Our boiler was a Glowworm flexicom 24cx, seemed to work fine for the 18months we were using it. The builder has advised that we replace it now during the build as it is a bit old and inefficient so I have some queries:

- What size boiler should I be looking to get (3 bed semi, 140sq/m)?
- Will there be sufficient pressure and flow rate for a good rain head shower and bath in main upstairs bathroom? If not what do I need to supply this, tank/pump?
- Any recommendations on make/type of combi boiler?

Note: the boiler will be located on the ground floor in the utility room below the bathroom. The extension will be adding 50sq/m to the house with 4 additional radiators.

Andyinter

kev1234 wrote: »

Bit of a novice but have a few queries on combi gas boilers. We are currently completing extension and refurbishment works on our 3 bed semi in Dublin. Our boiler was a Glowworm flexicom 24cx, seemed to work fine for the 18months we were using it. The builder has advised that we replace it now during the build as it is a bit old and inefficient so I have some queries:

- What size boiler should I be looking to get (3 bed semi, 140sq/m)?
- Will there be sufficient pressure and flow rate for a good rain head shower and bath in main upstairs bathroom? If not what do I need to supply this, tank/pump?
- Any recommendations on make/type of combi boiler?

Note: the boiler will be located on the ground floor in the utility room below the bathroom. The extension will be adding 50sq/m to the house with 4 additional radiators.

The boiler that is there is a condensing boiler in all fairness. But no it wont deliver to a rain head shower. You would need to boost from the tank in the attic through a pump & then into the cold feed for the boiler. A 24kW combi will only give about 9lpm of hot water at a 35 degree rise (cold water in @ 10 hot water out at 45). So go for at least a 32kW combi and get 14lpm to allow for the rain head. The current boiler you have will give about 18kw to the heating and as a ballpark with the extension your going to need between 18-20kW for heating (maybe less if you are insulating all external walls, replacing windows etc. Personally I would go for the Intergas combi boilers. Unlike other boilers they will also condense in hot water as well as heating. They have an incredibly robust heatexchanger, and again unlike other combi's they dont have motorized valves, divertor heads, plate heat exchanger's, auto air vents so less to go wrong. The heating output can also be adjusted to match the heating load required for the house

kev1234

Andyinter wrote: »

The boiler that is there is a condensing boiler in all fairness. But no it wont deliver to a rain head shower. You would need to boost from the tank in the attic through a pump & then into the cold feed for the boiler. A 24kW combi will only give about 9lpm of hot water at a 35 degree rise (cold water in @ 10 hot water out at 45). So go for at least a 32kW combi and get 14lpm to allow for the rain head. The current boiler you have will give about 18kw to the heating and as a ballpark with the extension your going to need between 18-20kW for heating (maybe less if you are insulating all external walls, replacing windows etc. Personally I would go for the Intergas combi boilers. Unlike other boilers they will also condense in hot water as well as heating. They have an incredibly robust heatexchanger, and again unlike other combi's they dont have motorized valves, divertor heads, plate heat exchanger's, auto air vents so less to go wrong. The heating output can also be adjusted to match the heating load required for the house

Thanks for the info and recommendation on boiler. I am a bit confused about the reference to the tank in the attic though. I thought if there is a combi boiler you don't need any tanks?

Or are you saying that in order to get the required pressure for a rain head shower that we would need a tank in the attic to pump water from this tank to the inlet of the boiler so there is sufficient flow into the boiler to create the pressure for the shower?

I need to check my mains water supply rate but is it possible that this would have sufficient flow to provide the shower? FYI, I will also have a bath but don't envisage this being used too often.

Andyinter

Water bylaws in Ireland state that only the cold tap in the kitchen & the tank in the attic are the only items allowed be connected to the incoming mains, everything else should be taken from the tank in the attic. While combi boilers are designed to be connected to mains, the mains pressure here is not great and nor is it guaranteed unlike our neighbors across the water. The idea of the pump is to guarantee pressure & taking from the tank always ensures water is present

kev1234

Andyinter wrote: »

Water bylaws in Ireland state that only the cold tap in the kitchen & the tank in the attic are the only items allowed be connected to the incoming mains, everything else should be taken from the tank in the attic. While combi boilers are designed to be connected to mains, the mains pressure here is not great and nor is it guaranteed unlike our neighbors across the water. The idea of the pump is to guarantee pressure & taking from the tank always ensures water is present

Ah right, I wasn't aware of that. As you can tell my knowledge to this point has primarily come from UK based articles/sites. Thanks for the info.

K.Flyer

kev1234 wrote: »

Ah right, I wasn't aware of that. As you can tell my knowledge to this point has primarily come from UK based articles/sites. Thanks for the info.

If you are going down the route of a combi boiler with the water taken from the tank via a pump, then you should consider a variable speed pump.
This type of pump will vary its speed / pressure depending on demand, giving long term savings on energy as well as noise and motor wear.

K.Flyer

K.Flyer wrote: »

If you are going down the route of a combi boiler with the water taken from the tank via a pump, then you should consider a variable speed pump.
This type of pump will vary its speed / pressure depending on demand, giving long term savings on energy as well as noise and motor wear.

Would a variable speed pump impact on the temperature at the tap?

kev1234

K.Flyer wrote: »

If you are going down the route of a combi boiler with the water taken from the tank via a pump, then you should consider a variable speed pump.
This type of pump will vary its speed / pressure depending on demand, giving long term savings on energy as well as noise and motor wear.

Should the tank be located in the attic or install a tank/cylinder and pump unit in the utility next to the combi boiler?

OP combis are usually looked at as a option when there is a reason to want to remove one ie space saving.

There is nothing wrong with your boiler if it meets the heating requirements, the changes in hot water delivery can cause some home owners to threaten to shot RGIs because they don’t understand/like the differences from their original stored hot water system .

If space saving isn’t a factor I’d look at a pump fed unvented cylinder as you would have the benefits of stored water ie water at a given temperature that doesn’t change if another tap is opened, secondary source of hot water from your electric immersion, quick cylinder reheat etc..

Combis are great machines but in larger houses they may not meet expectations.

Idbatterim

Your boiler is a modern condensing one. What is the cost going to be to change ? My family home has no tank bull**** , straight from the mains. Pressure fine!

If you have two showers operating at the same time, that may cause an issue , otherwise used no point in the vastly more complex and expensive system! Heating up Tons of water you don’t need etc. combi will give you instant, unlimited hot water on demand!

kev1234

gary71 wrote: »

OP combis are usually looked at as a option when there is a reason to want to remove one ie space saving.

There is nothing wrong with your boiler if it meets the heating requirements, the changes in hot water delivery can cause some home owners to threaten to shot RGIs because they don’t understand/like the differences from their original stored hot water system .

If space saving isn’t a factor I’d look at a pump fed unvented cylinder as you would have the benefits of stored water ie water at a given temperature that doesn’t change if another tap is opened, secondary source of hot water from your electric immersion, quick cylinder reheat etc..

Combis are great machines but in larger houses they may not meet expectations.

Idbatterim wrote: »

Your boiler is a modern condensing one. What is the cost going to be to change ? My family home has no tank bull**** , straight from the mains. Pressure fine!

If you have two showers operating at the same time, that may cause an issue , otherwise used no point in the vastly more complex and expensive system! Heating up Tons of water you don’t need etc. combi will give you instant, unlimited hot water on demand!

It's a 3 bed semi in Dublin currently 90sq/m, will be 140sq/m when complete. One main bathroom on first floor with 1 shower and a bath. Downstairs W/C (no shower/bath). The old hot water tank was in the bathroom but this has been removed to provide more space for the new bathroom layout.

I'm still a bit unsure of the distinction between a condensing boiler and a combi boiler. Can the existing Glowworm flexicom 24cx I have not act as a combi boiler?

kev1234

kev1234 wrote: »

It's a 3 bed semi in Dublin currently 90sq/m, will be 140sq/m when complete. One main bathroom on first floor with 1 shower and a bath. Downstairs W/C (no shower/bath). The old hot water tank was in the bathroom but this has been removed to provide more space for the new bathroom layout.

I'm still a bit unsure of the distinction between a condensing boiler and a combi boiler. Can the existing Glowworm flexicom 24cx I have not act as a combi boiler?

All gas boilers nowadays are pretty much condensing boilers.

You have a system boiler which heats you now defunct cylinder and can not be converted.

A combi is very similar to a system boiler albeit it can heat the mains water feeding your hot tap instantly.

kev1234

gary71 wrote: »

All gas boilers nowadays are pretty much condensing boilers.

You have a system boiler which heats you now defunct cylinder and can not be converted.

A combi is very similar to a system boiler albeit it can heat the mains water feeding your hot tap instantly.

This is very strange because the boiler we have did heat our mains water hot tap as well as the central heating so I assumed it was a combi boiler?

See below extracts from building survey report conducted on the house prior to the works:
"The property has the benefit of gas fired radiator system central heating throughout."
"Central heating is provided throughout via a series of pressed steel radiators fired by the Glowarm gas boiler located in the kitchen."
"Domestic hot water is supplied by the gas boiler, secondary electric immersion, and Mira shower heater."

kev1234

kev1234 wrote: »

This is very strange because the boiler we have did heat our mains water hot tap as well as the central heating so I assumed it was a combi boiler?

See below extracts from building survey report conducted on the house prior to the works:
"The property has the benefit of gas fired radiator system central heating throughout."
"Central heating is provided throughout via a series of pressed steel radiators fired by the Glowarm gas boiler located in the kitchen."
"Domestic hot water is supplied by the gas boiler, secondary electric immersion, and Mira shower heater."

If you had a cylinder/tank the boiler would heat the stored hot water in the tank first which would then allow you to draw hot water from the tank whereas a combi works by instantly heating the water that runs through it after you open a hot tap.

Idbatterim

A system boiler heats a hot water tank. The electric immersion in that tank is a back up , in case the boiler is out of action etc. there are combi boilers that have a small 50L tank built into them , for if two showers etc are running at the same time.

I’m not a plumber but i have researched the various systems. Just letting u know some of the various options...

K.Flyer

gary71 wrote: »

Would a variable speed pump impact on the temperature at the tap?

It shouldn't make any difference, or at least, no different than only partly opening a tap compared to fully.
The pump will modulate to demand, much in the same way as the boiler will.

kev1234

Met with my builder today and he advised that we go with a 30kw Worcester Greenstar combi boiler and grundfos pump next to the boiler being fed from tank in attic. I'm looking at a 30i or 29CDi model and wondering where can I source the boiler only?

K.Flyer

kev1234 wrote: »

Met with my builder today and he advised that we go with a 30kw Worcester Greenstar combi boiler and grundfos pump next to the boiler being fed from tank in attic. I'm looking at a 30i or 29CDi model and wondering where can I source the boiler only?

Most, if not all, plumbing merchants will only supply gas boilers to Registered Gas Installers.
Why would you not let the installer get it?

Ush1

Any chance you could post the price you were quoted? MOD NOTE: Only reply to this by PM please.

I got a combi installed a year and a half ago and am having issues.

kev1234

Ush1 wrote: »

Any chance you could post the price you were quoted? MOD NOTE: Only reply to this by PM please.

I got a combi installed a year and a half ago and am having issues.

Sorry for the delay in reply. Builder has quoted me €2,500 for supply and install of Worcester Bosch 30i including all pipework etc.

Ush1

kev1234 wrote: »

Sorry for the delay in reply. Builder has quoted me €2,500 for supply and install of Worcester Bosch 30i including all pipework etc.

That seems a very good price. I was charged over 4,500 for a Logic 24kw, does your quote include any zoning or heat controls?

kev1234

Ush1 wrote: »

That seems a very good price. I was charged over 4,500 for a Logic 24kw, does your quote include any zoning or heat controls?

No the €2,500 was just for the supply, install and commissioning of the new boiler.

The plan originally was to relocate the existing boiler and they had allowed €3,250 to "Build out new central heating system; new pipes, insulated throughout, fit in programmer, room stats, manifold, and motorside valves" so this figure will apply with the €2,500 additional for new boiler.

So my job now basically involves replacing the entire heating system. If yours is totalling €4,500 for everything then that seems good. If it's just the boiler replacement then it looks quite high.

Teazer

^ do you mind sending me your plumber for the Worcester as I'm in the process of replacing a boiler that has reached its end. We're in the same boat - 3BR in an end of terrace. The quotes I got were over 3k for Worcester + Honeywell Evohome. Although it allows flexi finance, I still think quote was over the top. How much warranty did you get? The one I got was 6 yrs - lower than the average of 7 years for Ideal. Thanks in advance!

Btw, if we have a separate plumber to install the Honeywell Evohome (another for the Boiler) - can we still get the €700 grant and the carbon tax grant €400?