Weather Compensator Underfloor Heating

patrickwoodcock

Hi,

Just had a query while I was thinking if I should get weather compensation on my boiler on a house im renovating.

So, combi boiler (possibly viessman) will supply hot water and also underfloor heating. I was hoping with the veissman and variable temp I wouldnt need a blending valve but have been advised I should have one. So, if I got a weather compensator that increased the water temp to the underfloor heating in colder weather, would the blending valve still mix the water at its set temp? IE would the weather compensator be a waste of money?

Thanks

Wearb

Assuming that it’s a temperature controlled blending valve (I have once seen it done with a gate valve) it should work well with weather compensation. The blending valve should let less cold return through as the supply temperature drops.

I think 🀔 Those squiggles are meant to be a thinking emoticon

patrickwoodcock

The weather compensator is part of the boiler, not the valve

Wearb

patrickwoodcock wrote: »

The weather compensator is part of the boiler, not the valve

Yes it reduces water temperature leaving the boiler when outside temperature rises

patrickwoodcock

Wearb wrote: »

Yes it reduces water temperature leaving the boiler when outside temperature rises

Thank you. I get that, but the blending valve is a seperate entity that has a set fixed temperature, so if the blending valve has a fixed temp mixed rate, if for instance the weather drops outside, the boiler will increase its temperature, but the blending valve will just mix more cold water, as it’s fixed? Or have I this wrong?

Wearb

The blending valve maintains the set output temperature by varying the ratio of hot to cold.

I think I might be missing the point you are trying to understand, so have another go at it if you like.

Dtp1979

Weather compensation on a gas boiler automatically adjusts the boiler control stat according to the outsid temp.

Weather compensation on an oil boiler automatically adjusts the mixing valve to suit the outside temp.

antoinolachtnai

If you could set the mixing valve to the highest allowable temperature for the UFH, and set the boiler quite low, then the weather compensation will control the temperature of the UFH? Does this sound right?

You would need to get the view of the manufacturers for an arrangement like this I suppose.

rolion

patrickwoodcock wrote: »

Hi,

Just had a query while I was thinking if I should get weather compensation on my boiler on a house im renovating.

So, combi boiler (possibly viessman) will supply hot water and also underfloor heating. I was hoping with the veissman and variable temp I wouldnt need a blending valve but have been advised I should have one. So, if I got a weather compensator that increased the water temp to the underfloor heating in colder weather, would the blending valve still mix the water at its set temp? IE would the weather compensator be a waste of money?

Thanks

Been there myself years ago.
I was thinking to get the Viessmann dedicated UFH extra module.

In the end,i separated the zones.
Left gas boiler with hot water and with the radiators.
For UFH went with something like below,more or less same principle as a mixing valve but with much better controls,external to the gas boiler and no weather compensating as the insulation of the house can trigger false positives.

I advise you to check with a local reseller of Viessmann (i can get you in touch with one) and get the right pro advise.

rolion

I was working based on this diagram here:





I have a 80 page PDF from Caleffi regarding mixing in boiler and ufh but i cannot upload it here.

Wearb

If you want to make the pdf available here, just upload it to Dropbox or similar and post link here.