Gas boiler electrical consumption

[DyerMaker]

Hi all, I'm wondering about electrical power consumption on Gas boilers - both combi and heat-only.

I've seen quite a large variance in ratings, some being only 25W, other 150W.

As far as I can reason, I'm guessing the two main sources of current draw would be the flue fan and the circulating pump, and of those two, most likely the pump would draw the most.

So maybe the lower-rated ones I've seen don't have an integrated pump... I can't recall off-hand.

I ask because I'm on renewable energy so these things are key. Currently, I have a grundfos circulating pump on my solid fuel system that is nearly always on its lowest setting and draws about 7-10W - it's a small system, 3 small single rads and one double, plus an indirect cylinder, open vented, everything is close together with no gravity to overcome as its all on one level.

I'm hoping to add a gas fired boiler to my system so I can set a timer for cold mornings, etc.

The question is, would a boiler with integrated pump also only draw a low Wattage in my system, even though it might be rated at 150W - that being a maximum, rather than a constant? I could be wrong, but I wouldn't expect the flue fan to draw much more than 35W or so... which my batteries/inverter can probably cope with, but if a boiler is going to expect 150W (or more, factoring in start-up draw) on a cold morning, that might be pushing it a bit if my batteries haven't had a good charge the day before.

Appreciate any advice, cheers

 

[cross thread]

All the data you required will be on the manufactures info

 

[DyerMaker]

All the data you required will be on the manufactures info

yup.. for example - rating is 150W... but that's a MAX figure, what the installation manual doesn't tell me is it's current draw under different conditions...

so was asking if others with experience of such things might have some real-world examples.

 

[Gasguru]

At maximum output the fan & pump may well consume those figures but it will be considerably lower once it modulates down.

I'd be more concerned with whether the inverter can cope with the inrush current demand on initial power up...on a combi/system boiler the main pcb, fan and
pump (and just the pcb & fan on a heat only) have bulk capacitors and their significant current demand is normally only limited by NTCs.

 

[Ihavenojob]

How would a modern boiler react to being run off batteries/inverter?. Used to have problems with certain makes that wouldn't rectify when powered by generators used by the Electricity Companies during major grid works.

 

[DyerMaker]

How would a modern boiler react to being run off batteries/inverter?. Used to have problems with certain makes that wouldn't rectify when powered by generators used by the Electricity Companies during major grid works.

Probably wouldn't react well to voltage fluctuations. Thankfully my generator is pretty solid in terms of voltage and I have a good pure sine wave inverter. I have no trouble with washing machine, computers, etc.

I've done a bit more research and I think I'll be looking for a heat only boiler designed for an open vented system. I think I'm right in saying these don't have an integrated pump but rather are designed to work with an existing circulating pump. As such, they have a much lower current draw and the ratings are around 20-30W.

 

[vulcancontinental]

A Grunfos OEM pump in a boiler has a draw of 4 to 39W compared to the old style of up to 100 or so. Not sure what the latest Riello (Taco) pump draw is.

 

[DyerMaker]

That's what I currently have in my solid fuel system - a Grunfos alpha 2, generally runs at about 7-9W on stage 1 setting. If I need to heat water quickly, I switch it to auto-adapt mode which varies up to about 19W. fantastic bit of kit, been running hassle free over 10 years now. It'll go up to 45W on stage 3 setting but I never use that.

 

[muggles]

You'll struggle to find a heat only boiler that will modulate low enough to run your small system efficiently. I'm also concerned that you're expecting that you can just connect the new boiler's flow and return into the existing system, which already sounds like it's not been fitted correctly. It's a bit more complicated than that, assuming you want to do it correctly. For a start you need to consider how to safely prevent heated water circulating around the appliance not in use and wasting energy.

 

[DyerMaker]

You'll struggle to find a heat only boiler that will modulate low enough to run your small system efficiently. I'm also concerned that you're expecting that you can just connect the new boiler's flow and return into the existing system, which already sounds like it's not been fitted correctly. It's a bit more complicated than that, assuming you want to do it correctly. For a start you need to consider how to safely prevent heated water circulating around the appliance not in use and wasting energy.

My intended use for the gas boiler would be for a short run on a timer, mostly cold winter mornings. I might also want to use it as an alternative means for heating water in summer rather than lighting a fire. Was looking at the vaillant ecotec range the smallest of which is 12kw.
Interested to know what makes you suspect the existing system is not fitted correctly? Even though I suspect you are right!

 

[Gasguru]

Adding a gas boiler onto a solid fuel system requires various additions to ensure the safety of each system is not compromised.
Many companies specialise in combining solid fuel and gas/oil boilers...

http://dunsleyheat.co.uk/neutralizer.html

 

[muggles]

My intended use for the gas boiler would be for a short run on a timer, mostly cold winter mornings. I might also want to use it as an alternative means for heating water in summer rather than lighting a fire. Was looking at the vaillant ecotec range the smallest of which is 12kw.
Interested to know what makes you suspect the existing system is not fitted correctly? Even though I suspect you are right!

4 small radiators suggests your system is no more than 4kW, probably less. A 600mm high 1000mm wide single panel radiator is about 1kW.

You've said everything is on one level, which is incorrect as the cylinder is required to be at least a metre higher than the stove. You also seem to suggest that the entire system requires the use of the pump in order to circulate. Again, this is incorrect as it presents a potentially dangerous situation in the event of electrical or pump failure. At least 15% of the stove's heating capacity should be designed to circulate without the use of any electrical apparatus. This is usually the cylinder plus one or two radiators.

 

[DyerMaker]

4 small radiators suggests your system is no more than 4kW, probably less. A 600mm high 1000mm wide single panel radiator is about 1kW.

You've said everything is on one level, which is incorrect as the cylinder is required to be at least a metre higher than the stove. You also seem to suggest that the entire system requires the use of the pump in order to circulate. Again, this is incorrect as it presents a potentially dangerous situation in the event of electrical or pump failure. At least 15% of the stove's heating capacity should be designed to circulate without the use of any electrical apparatus. This is usually the cylinder plus one or two radiators.

I see! Your powers of deduction have gotten the better of me! When I said everything on one level I really meant there's no upstairs, hence no appreciable gravity for the pump to have to work against... but you are actually right I didn't place the tank as high as it should be ideally. As for the pump - I actually thought of that and have a gate valve that I use as a manual bypass when the pump is off. Again, you're right though since if the pump were to fail unexpectedly there COULD be trouble theoretically, although in practice the excess pressure just vents into the expansion tank (on the few occasions I've forgotten to turn the pump on).

Well, that's why I'm here - to learn!

 

[muggles]

The problem with using the expansion tank as a heat dump is that it can affect its structural integrity if it gets too hot. Also, if the heat can't get away quick enough it'll flash to steam inside the stove, which is not good news at all. Is the tank one which is correctly rated for a solid fuel system, with a copper float on the ball valve?