Combi Boiler with UFH

[Dan Robinson]

But.....

 

[JohnD]

ODFOD

 

[John D v2.0]

To be fair i see your point and as I admitted I didn't spot it was an oil boiler, and clearly the op was referring to linear modulation rather than anything other kind.
My only point is you needn't match your heat output to t minimum output of any boiler, as all boiler can cycle on and off I they over shoot the flow temp.
At the start and end of the heating season, especially when the trvs close on most radiators, there aren't many boilers that could lineally modulate low enough, werew taking a kW or lower. So it can't be a big issue.

 

[Dan Robinson]

It can be an issue with oil boilers. They're simply not geared up to lots of start stop.

Also though, linear modulation of a burner in a gas boiler has nothing to do with own pwm.

 

[John D v2.0]

It can be an issue with oil boilers. They're simply not geared up to lots of start stop.

Also though, linear modulation of a burner in a gas boiler has nothing to do with own pwm.

Thanks for the info re oil burners. Indeed, linear modulation in a modern gas boiler is just changing the fan speed which is an EC motor. But once it needs below the minimum, it will be on for 10 minutes or whatever, and off until the anti cycling time elapses and the water temperature drops. So an extremely slow version of PWM. This doesn't matter until you have very low thermal mass so your place cools down before the boiler kicks in again.

 

[muggles]

Oil combi boilers are generally a bit rubbish. If you can get a regular boiler and unvented cylinder setup that is always the best option, or even a thermal store. There's no modulation on oil boilers yet (give it a couple more years), with the exception of Viessmann who will sell you one for about £6k.

 

[wcavanagh]

Thanks everyone for the input. Reason for combi is space number 1, the boiler house is small. Secondly we work all day, and don't use that much hot water, so it makes sense to heat water only when we need it. Seems crazy to either store 300L of hot water all day or heat 300L of water for the little use that night.

So a wee buffer tank on the central heating side, will help the boiler heat a larger volume of water I assume than what the UFH has, and help avoid this short cycling.

 

[wcavanagh]

I assume I need something like this.

 

[Roger928]

If you install that contraption you might as well fit a smaller boiler (sized to the heat load) and fit an unvented cylinder.

 

[wcavanagh]

Seems people are using a 2 connection system these days. Like this.

 

[Dan Robinson]

No. That is a heat pump. The buffee vessel is for different reasons (And the same). Its volume won't do anything meaningful for an oil boiler.

 

[wcavanagh]

I can find no reference to a buffee vessel on google. Do you have a link to any info. All the info I find online for BUFFER vessel talk about stopping short cycling, for heat pumps etc. Is that not what we are trying to do here?

 

[wcavanagh]

I did however come across slimline heat store. Maybe this is an option with just a system boiler? Are modern heat stores economical