Combination Units

bovide_4

Triangle Tube's website for combo units.

Jim_65

Combination Units

Fellow Wallies,

I am looking for some quality feedback (Good, Bad, Indifferent) with Combination boiler & DHW (Flat Plate-Internal) options.

What brands/models have you had great success with?

Design flaws? Limitations? Expected performance? Longevity? Things you would do differently?

All ideas and comments are welcome on what you would consider to be a good application for one of these units. I have potential clients with smaller projects (overall square footage, available mechanical space, DHW & Heat load demands, etc.)and would prefer to have an option to present without hesitating on expected performance. I am sure that I am not alone with this design dilema.

Thank you in advance!

Andy Byrnes

Hi Jim

I live and work in the UK and have been fitting, repairing and servicing combi boilers for about 15 years. Here is a list of my pro's and con's.

Manufacturers are producing smaller boilers because customers want them hidden in cupboards, like kitchen units. Now that may sound nice but unfortunately I like to able to get my hands in to work on them and not keep banging my head on the shelf above. Also us heating engineers are not all blessed with ladies hands so the more room in the boiler the better.

Boilers are now available with higher outputs this is because the older units had rubbish flow rates for hot water. The boilers could cope with the heating load but you try running two taps at once and you had no chance. Manufacturers are now producing boilers with unvented heat stores attached to them, which can supply better hot water flow rates.

The most important bit of advice I could give to anyone installing a combi is to make sure the system is cleaned thoroughly and have some form of inhibitor added to prevent a build up of debris in the system. I have found the main cause of breakdown on combi ‘s is magnetite, if it enters the boiler it will give reduced efficiency by clogging the plate-to-plate and main heat exchanger and increase component failures.

Some Manufactures are producing extremely reliable combi boilers and more recently
Giving a 5-year warranty (as long as the boiler is installed and cleansed properly).
The only one I have come across that is available in the USA and Canada and is like what we have in the UK is the Baxi. This has become a heating engineers choice of boiler. It is easy to install and you can get your hands in to work on it. Fault finding and servicing is straightforward and it has proved a quite reliable boiler.

These are my own opinions, hopefully some one else share theirs too.

Andy B.

Bob Sweet

I agree with the Baxi

as being a good choice for the combo. I think a good idea would be to add something like the Webstone valves to the flate plate hx ports, this would allow for the cleaning of deposits that WILL collect in the flat plate hx. You could include it in the yearly maintenece of the unit.

The other thing to consider, is the limitations of flow through the flat plate. 3.5 to 4 gpm is about the max. flow your going to get through the domestic side of the unit. Easily worked around with some strategic planning of hot water needs but something to consider.

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Jim_65

I am

already aware of the Baxi. Do they only produce it in the one size for the DHW load? The heat loss of some of these projects is approx. 50K.

I appreciate the input and will keep the Webstones in mind for future service.

Thanks again!

Andy Byrnes

I believe they have the Baxi's with a heat store for increased DHW capacity.

Andy B.

Jim_65

Sorry

Andy I guess I missed that in your first post.

To clariy what exactly do you mean by heat store?

I thought I understood what you were implying by the increase in DHW production but I may be missing an obvious point.

Andy Byrnes

Like an unvented hot water cylinder attached to the boiler unit. These are usually fast recovery so if the heat store is depleated it can reheat in 5 to 10 minutes.

Can't find any Baxi's to show you but I'm pretty sure they do them. I may be able to find an alternative manufacturer's boiler to look at just so you get the jist.

I will pop the web sit up when I find it.

Andy

Andy Byrnes

Have a look at this brochure. This is a Saunier Duval ( a company I used to work for but unfortunatley they are french )

I think it may help in explaining what I mean. I can't find the Baxi equivilent yet to show you.

Andy.

Andy Byrnes

I will try that again.

http://www.saunier-duval.co.uk/manuals/pdf/ISOTWIN CONDENS.pdf

Andy

Jim_65

Andy

Thank you now I have a visual of what you were implying.

I have never come across that company prior to that.

Thank you for your assistance and beneficial information that you provided.

Take care,
Jim F.

Bob Forand

Baxi

Baxi have 2 different models with a plate exchanger. Both are capable of supplying 100+k BTU for hot water production, then modulate for the heat production. They have a 3 way diverter valve that creates priority for the hot water. The 310FI will produce 3.3 GPM, and the HT330 will produce 3.6 GPM for DHW. So yes the boilers are more than capable of heating 50K for the heat and 105K for hot water production.

Bob Sweet

Actually

the 310fi uses a pressure actuated valve utilizing a diapragm to divert the water between heating and domestic. The HT utilizes a motorized 3-way diverter valve for heating and domestic production.

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Joe Brix

I believe Laars

now resells the Mascot line. (Re-labeled Baxi's) Other better option could be wall hung boiler with a small low-boy indirect under it. Now you have 2 seperate unit's. Better efficency and easier to repair and maintain.

Jim_65

Limited

on available mechanical space but I would prefer to install a boiler/tank setup. Thank you for the suggestion.

I will look at the Baxi models and see what may be the best offering.

Thank you to all for their input. I appreciate it!

Marty_9

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