New OIL boiler choice

[Exedon]

That seems a bit of an obvious design flaw. I wonder why they don't make it out of stainless steel.

Better be absolutely clear about the Grant boiler.
The secondry heat exchanger is stainless steel and that's where the heating return connects into.
Recommended return temperature when up to temperature of 50 but not below 40.
I wouldn't argue that houndsfield boilers are ok but there range is small, no combi (I'm away of there rational for that) so there range covers less than 40% of the oil boilers we fit .

 

[JonathanM]

The secondry heat exchanger is stainless steel and that's what the heating return connects into.
Recommended return temperature when up to temperature of 50 but not below 40.

Thanks. I've just been reading the manual:

The boiler should not be allowed to operate with return temperatures of less than 40°C when the system is up to temperature

On the face of it, (to a lay person!), that seems a bit strange. Why don't they just make it out of stainless steel? Is it purely cost, or are there other design considerations? I wonder whether this limitation is take into account, when doing the efficiency tests?

They seem very proud of their design, because they promote their "award winning Vortex stainless steel condensing heat exchanger". This presumably is the secondary. Do other oil boilers have a single heat exchanger? Maybe there is an advantage to having a secondary heat exchanger?

 

[JonathanM]

I know nothing about oil boilers, so found this interesting. I had no idea there was such a difference between fuels.

 

[delberto]

I haven't, I just believe in installing quality products rather than mass-manufactured stuff with built in design flaws

I suspect you're just looking at different sets of figures though. The 15/21 was most likely rated using the SEDBUK 2005 figure, whereas the 15/26 uses SEDBUK 2009. If you look at the technical data in the manual where both models are listed, you'll see on Page 7 that the 15/21 is rated at 91.2% and the 15/26 at 91.9%, so there's naff-all in it.

Thanks Muggles,

the brochure On my work website is about 6 years old and as you guessed based on sap 2005 calcs.

The 21KW unit it is then- as it’s A bit smaller which will help with where it is being located.

cheers

 

[Johntheo5]

Thanks. I've just been reading the manual:



On the face of it, (to a lay person!), that seems a bit strange. Why don't they just make it out of stainless steel? Is it purely cost, or are there other design considerations? I wonder whether this limitation is take into account, when doing the efficiency tests?

They seem very proud of their design, because they promote their "award winning Vortex stainless steel condensing heat exchanger". This presumably is the secondary. Do other oil boilers have a single heat exchanger? Maybe there is an advantage to having a secondary heat exchanger?

I would think the reason for a OF boiler having two heat exchangers is because the heat exchanger is just a box basically unlike a gas fired boiler where the water is fed through a single pipe, the Hx is just a "pipe" really, the longer the tube the lower the temperature. On my SE Firebird, the feed temperature makes little or no difference to the fluegas temperature . The reason for the 40C minimum feed temp to the Grant OF boiler is that the gases leaving the primary Hx would still be too cold to avoid corrosion in the secondary MS Hx.

 

[JonathanM]

I would think the reason for a OF boiler having two heat exchangers is because the heat exchanger is just a box basically unlike a gas fired boiler where the water is fed through a single pipe, the Hx is just a "pipe" really, the longer the tube the lower the temperature. On my SE Firebird, the feed temperature makes little or no difference to the fluegas temperature . The reason for the 40C minimum feed temp to the Grant OF boiler is that the gases leaving the primary Hx would still be too cold to avoid corrosion in the secondary MS Hx.

Thanks for this information. I had no idea that oil boilers were so different.

I don't think it's just Grant. I've found another oil boiler manufacturer, who gives the same advice, for the same reason. In fact, they say minimum return temperature is 50C.

It does seem a bit bizarre to me, on the face of it, to go to the trouble and expense of designing and manufacturing a condensing boiler, and then tell customers that they must not actually make it condense, or the main HX will corrode, and invalidate the warranty. It also seems to be against the spirit, at least, of the rules on condensing boilers.

But bearing in mind it's more than one manufacturer doing it, I'm guessing there is a good reason. Maybe there is something about oil boilers, which means they just aren't suited to condensing.

I was wondering how the new rules on 55C flow temperature will work. The return will certainly be below 50C, and very likely under 40C. Are oil boilers exempt?