Understanding boiler MINIMUM heat output

[caravanboy]

I am currently refitting a static caravan for use during a house build/renovation. The previous owners of the caravan had fitted small central heating radiators and used a combi boiler in an external shed sited adjacent to the caravan.

I have purchased the caravan but not the boiler as they have now fitted that to their new house so I need to find a suitable boiler.

The radiators are very small and I am concerned that they will not take out enough heat to stop the boiler or pipes overheating (there is some evidence this has happened in the past as some of the climaflex style pipe insulation has melted). I have calculated that the current radiators can take out approx 3kW. A few combi boilers I have looked at have minimum heat outputs of around 9kW.

So, to my questions - have I understood correctly that the minimum heat output means the minimum the radiators must take? If so, if I got a modern boiler with a suitable internal bypass, how is it different to only taking out a few kW of heat using all the radiators versus the situation in a house that may occur where say the majority of radiators' TRVs have closed off thus leaving only one or two to take the heat out of the system? Am I missing something here? Perhaps minimum heat output is to do with the Hot Water aspect of the boiler?

In general, are there modern boilers that will modulate right down and only heat the water in the heating circuit enough to meet the demands of the radiators that are fitted? Can anyone recommend one that may be suitable (and cheap) as we'll be getting rid in a year or two once the house is built (with a Ground Source Heat Pump so no need for the boiler).

Thanks.

 

[Doctor Drivel]

the best modulates down to 3kW, but expensive. You can fit a small heat buffer cylinder (can a normal domestic cylinder is open vented. between the boiler and the rads. The boiler heats this and is switched via a two stats to prevent boiler cycling. The flow and return to the pipes is taken off this cylinder. The boiler only heats the buffer in one long burn and then off. The rads trickle out the heat from the buffer as need be. Have TRVs on all rads and use Grundfos Alpha smart pump on the CH pipes.

 

[Gasguru]

the best modulates down to 3kW, but expensive. You can fit a small heat buffer cylinder (can a normal domestic cylinder is open vented. between the boiler and the rads. The boiler heats this and is switched via a two stats to prevent boiler cycling. The flow and return to the pipes is taken off this cylinder. The boiler only heats the buffer in one long burn and then off. The rads trickle out the heat from the buffer as need be. Have TRVs on all rads and use Grundfos Alpha smart pump on the CH pipes.

All this for a temporary lash up in a caravan


You could just stick in a couple of electric heaters with an electric shower. Otherwise any combi will do the job. Many combis run at maximum output on just a couple of radiators without problems. Install room thermostat.


Are you sure you've researched the ground source lark? did they mention you must buy green energy (if you're doing it to help the environment) and double space the underfloor pipework? What's the seasonal COP?

 

[Doctor Drivel]

the best modulates down to 3kW, but expensive. You can fit a small heat buffer cylinder (can a normal domestic cylinder is open vented. between the boiler and the rads. The boiler heats this and is switched via a two stats to prevent boiler cycling. The flow and return to the pipes is taken off this cylinder. The boiler only heats the buffer in one long burn and then off. The rads trickle out the heat from the buffer as need be. Have TRVs on all rads and use Grundfos Alpha smart pump on the CH pipes.

All this for a temporary lash up in a caravan

The idea is to stop cycling. the cheapest and best way.

You could just stick in a couple of electric heaters with an electric shower. Otherwise any combi will do the job. Many combis run at maximum output on just a couple of radiators without problems. Install room thermostat.

Do you know much about modern combis? 24kW????

 

[Gasguru]

Here we go again - can't resist talking **** can you......ITS A TEMPORARY INSTALLATION IN A CARAVAN

Are you really suggesting they go to the trouble of your proposed setup (not to mention the extra space it requires) just to save a tiny amount on the gas bill. Tell us payback on your setup and the extra cost involved.

As you are well aware there are hundreds of thousands of combis installed in flats with just a couple of radiators - the systems work pefectly OK. They just modulate down and with the room stat are all perfectly happy. ok they may not be as efficient as they could be but the payback with extra complexity is not worth it for such a small heat load.

 

[htgeng]

The Atag E22c combi will modulate down to 4.4kw for central heating and still provide a peak 25kw for the hot water. When you are done with the caravan, you will want it in your house!

 

[Gasguru]

The Atag probably costs more than the caravan

 

[megawatt]

Presumably Doc Drivel isn't an installer?

If he were ... He'd starve

 

[Dan Robinson]

As well as Ground-source look at Air source.

One set up I know of has a twin level cellar.

Freezers for meat in top cellar with Air-heat pump installed. Discharge from air heat pump run to cellar underneath where the wine is kept.

Wasted Heat from freezers is used to lower the COP.

I want to get there and look at the set up; but it is the father-in-law of a former employee in Ireland which makes it a little awkward.

 

[Balenza]

Dan
Having a half ton of beef or so frozen in your home freezer is not something you would want in order to justify "rising" (as opposed to lowering) the cop of a heat pump in a heat recovery set up.

Not unless you own a large butchers shop with an abundance of chilling facilities and your living next door to it that is.

 

[Dan Robinson]

But I like Beef.

 

[gas4you]

Is that beef curtains Dan (sorry been on pittle since 6 and now opened another litre of bacardi )

 

[Dan Robinson]

I love chomping on Salmon fillets to mate .

 

[jon26]

As you are well aware there are hundreds of thousands of combis installed in flats with just a couple of radiators - the systems work pefectly OK. They just modulate down and with the room stat are all perfectly happy. ok they may not be as efficient as they could be but the payback with extra complexity is not worth it for such a small heat load.

Gasguru is completely right... 80% of boilers installed nowadays are combi's (no doubt someone will say 79% or something silly!) Anyway, most of them serve small flats with 3 or 4 rads with an output requirement of nowhere near 9kW and they work fine.

Just put in a small combi.... do not lose sleep over it.

Heat pump = many £'s plus HW cylinder plus many £'s on U/F htg... lose this idea straightaway

did anyone see that TV series - Its Not Easy Being Green they should re-word it 'Its not Cheap Being Green' !!

 

[jon26]

Just realised this was a very old post but couldn't resist a reply!!