Enclosing a gas water heater - air requirements?

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elpenguino

3392 posts

Uber Geek

#319049 17-Mar-2025 20:25

We have an infinity water heater in a cupboard. You can see the flame through an opening so I am pretty sure it draws air from the room , not outside.

Currently the cupboard has louvered doors but la penguina wants to change the doors for something else, perhaps a plain / solid door.

Does anyone know what the legalities for ensuring airflow are?

I suppose vents in the doors are another option (probably with requirements around those too) - what are my other options?

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

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20108 posts

Uber Geek

#3354684 17-Mar-2025 20:52

Aren’t they supposed to be normally installed outside? I have seen one installed in the roof space of a house before but that would have a lot of airflow around it and air coming in from gaps around roof. I rotor suggest reading the installation instructions of the model you have to see its installation requirements.

wellygary

8266 posts

Uber Geek

#3354694 17-Mar-2025 21:20

Its exhaust must be vented outside, these instructions say that it has a "double walled" exhaust to allow it to draw from the outside as well as expel fumes out...

"Flueing options The flueing for internal water heaters is a coaxial design. It has a stainless steel inner pipe to discharge products of combustion and a thermoplastic outer pipe for air supply to the appliance".

https://rinnai.co.nz/wp-content/uploads/2024/11/inf-stainless-flue-install-11748-i-9-24.pdf

elpenguino

3392 posts

Uber Geek

#3354704 17-Mar-2025 21:48

Thanks, its exhaust is to the outdoors through a pipe in the roof.

The cupboard is sufficiently large for the device not to heat anything around it.

I'm specifically interested in regulations about the intake air requirements, if that's a thing.

It's an ancient model but yes, do I have a model no or manual .....

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

pih

649 posts

Ultimate Geek

Lifetime subscriber

#3354721 18-Mar-2025 06:43

Common sense would indicate that you need a vent with at least the same cross sectional area for fresh air intake as you currently have in the exhaust flue, otherwise you could create enough negative pressure in the cupboard that combustion and/or cooling in the unit is affected. I'd go with a safety margin of double that just to be safe.

Bung

6402 posts

Uber Geek

Subscriber

#3354730 18-Mar-2025 08:18

elpenguino:

I'm specifically interested in regulations about the intake air requirements, if that's a thing.

It's an ancient model but yes, do I have a model no or manual .....

Have you read wellygary's post? Unless the older internal systems are quite different to current models, intake air is ducted from outside in the outer ring of the flue.

johno1234

2741 posts

Uber Geek

#3354743 18-Mar-2025 08:58

Interesting. Seems like an expensive choice to install internally with the requirement for a flue and even worse you have to penetrate the roofing and flash around the chimney. Easier and cheaper to just bolt it to the exterior of the house.

elpenguino

3392 posts

Uber Geek

#3354754 18-Mar-2025 10:05

Bung:

elpenguino:

I'm specifically interested in regulations about the intake air requirements, if that's a thing.

It's an ancient model but yes, do I have a model no or manual .....

Have you read wellygary's post? Unless the older internal systems are quite different to current models, intake air is ducted from outside in the outer ring of the flue.

Yes I have but I've probably confused the situation by using the word infinity (little i) as infinity might be a Rinnai product name (big i).

I'm pretty sure this thing, which is a Bosch WR325 , takes its air from the room because I can see the whole flame array when the thing is working.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

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elpenguino

3392 posts

Uber Geek

#3354755 18-Mar-2025 10:08

pih:

Common sense would indicate that you need a vent with at least the same cross sectional area for fresh air intake as you currently have in the exhaust flue, otherwise you could create enough negative pressure in the cupboard that combustion and/or cooling in the unit is affected. I'd go with a safety margin of double that just to be safe.

That does indeed sound sensible. Do you have any information about regulatory requirements for these vents, if there is such regulation ? Height above floor, materials?

I would need to make sure any doors I get , or get made, are not only legit but also meet the stringent requirements of the boss.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

elpenguino

3392 posts

Uber Geek

#3354756 18-Mar-2025 10:12

johno1234:

Interesting. Seems like an expensive choice to install internally with the requirement for a flue and even worse you have to penetrate the roofing and flash around the chimney. Easier and cheaper to just bolt it to the exterior of the house.

Thing was installed 25 years ago, long before we bought the house.

It's a very basic thing and it doesn't give any trouble so we'll probably stick with it for while.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

Bung

6402 posts

Uber Geek

Subscriber

#3354760 18-Mar-2025 10:24

elpenguino:

Yes I have but I've probably confused the situation by using the word infinity (little i) as infinity might be a Rinnai product name (big i).

I'm pretty sure this thing, which is a Bosch WR325 , takes its air from the room because I can see the whole flame array when the thing is working.

On line description of the WR325 is same as the internal Rinnai. The air for normal use comes from outside. The intake duct surrounds the exhaust. Whether or not any other venting is needed is a question for Bosch or a gas fitter. I know some gas fitters are GZ members but can't remember who.

Edit @WWHB might know.

Scott3

3947 posts

Uber Geek

Lifetime subscriber

#3354772 18-Mar-2025 10:57

elpenguino:

Yes I have but I've probably confused the situation by using the word infinity (little i) as infinity might be a Rinnai product name (big i).

I'm pretty sure this thing, which is a Bosch WR325 , takes its air from the room because I can see the whole flame array when the thing is working.

First thing to work out is if it uses room air for combustion.

As an example, this one does not, using an air intake from the flue shroud.

https://installer.alpha.worcester-bosch.co.uk/support/literature/download/release/6720605998/12866

And the manual only set out clearances, not any need for ventilation.

This one also uses outside air for combustion.

https://www.gassupportservices.co.uk/f/m/Worcester/Other%20Equipment%20&%20Information/installation-and-servicing-instructions-for-wr-325-bf.pdf

But has cooling vent requirements in section 6 if you want to install it in a cabinet or cupboard

elpenguino

3392 posts

Uber Geek

#3354790 18-Mar-2025 11:42

Looks like this general model has a few variations. I found the model label inside (WR-325-1 KV1 B23) and eventually found the exact manual here.

https://bosch-au-en-techdoc.boschtt-documents.com/download/file/file/6720605088.pdf

The manual has a decode of the model information as:

W Multipoint gas water heater
R Automatic power adaption
250 Code number 17,5 kW (250 kcal/min)
325 Code number 22,75 kW (325 kcal/min)
400 Code number 28 kW (400 kcal/min)
-1 Version code number
K Chimney flue
V Connector
1 Temperature selector
B Battery ignition
23 Gas code number, natural gas H

However, when you search for 'flue', the manual says 'Use approved single or twin skin flue in accordance with AG601'.

I would have thought a single skinned flue would make it impossible to draw air in at the same time as expelling exhaust ( but what do I know?) .

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

djtOtago

1142 posts

Uber Geek

#3354796 18-Mar-2025 11:59

Don't know what the regulations are, but one of the flats I was in 30 years or so ago had one. The door to the cupboard it was in had a 50mm gap at the bottom.
I have to say it was a brilliant unit. It was only about 200 litres. (45 gal) On piped gas in a flat with 4 girls, 2 boys, we never ran out of hot water and the gas bill was cheap. Those were the days.

wellygary

8266 posts

Uber Geek

#3354812 18-Mar-2025 14:17

djtOtago:

Don't know what the regulations are, but one of the flats I was in 30 years or so ago had one. The door to the cupboard it was in had a 50mm gap at the bottom.
I have to say it was a brilliant unit. It was only about 200 litres. (45 gal) On piped gas in a flat with 4 girls, 2 boys, we never ran out of hot water and the gas bill was cheap. Those were the days.

I doubt it,
180 litre is a regular 1.7m tall HWC,

"Infinity" units only heat what they need so in reality the heating chamber is only a couple of litres at most

Gas endless is still the only solution for a high demand and high variability Hot water solution...
You can do it with electricity but its a bit like standing under a watering can in comparison....

djtOtago

1142 posts

Uber Geek

#3354819 18-Mar-2025 15:20

I guess it must have been 45 us gallons then. Not that it really matters.

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