Can a 50,000 Boiler handle total output 65,000 - 70,000?

[tomjones1234]

Hi all,

Firstly what a great forum, some good questions and knowledge. Was wondering if could seek some advice from those in the know. We've had a problem with our heating in the house, i.e the downstairs gets hot and the upstairs remains cold even if the heating has been on for 5-6 hours.

The house is a 4 bedroom detached, all insulation is fine, including loft insulation and cavity. We've seeken advice from a heating engineer who has indicated that the 4 upstairs radiators are too small for the rooms. Thus we need to change these to large double flinge ones.

Our existing boiler is a Potterton Profile 50B (Balanced flu). The total output with the new radiators will total 65,000 - 70,000. We're a bit scared now as we're thinking the boiler will pack in? The advice from the heating engineer is that it will take longer to heat and thus will get warm but in about 1-2 hours.

Can anyone assist and indicate if we are proceeding in the right direction?

Cheers
Tom

 

[corgiman]

the boiler will never shut off and it will cost you a fortune and eventually kill the boiler

the one option you have is to replace the boiler, its not as new labour say ALOT "fit for purpose"

 

[ChrisR]

upstairs remains cold

Do the rads get hot though?

Your 65-70,000 is based on an inside - outside temp difference of say 21 degrees.
SO your 50k will roughy manage 15.5°, so you'll be chilly if it goes below 5 degrees or so.
Cheapest option might be to get a couple of oil-filled rads at 3kW each. They have timers and thermostats. And see how it goes.

 

[tomjones1234]

Hi Chris,

Yes, the radiators do get hot. Seems like we have been given the wrong advice then, wouldn't want to push the boiler making it work harder. Our initial approach was let the boiler break down upon which we would replace it? Good or bad?

Cheers,
Tom

 

[corgiman]

Bad idea as if it breaksdown on xmas day you are going to have a bit of a wait for someone to do the work.

 

[ChrisR]

Why should it break down? It'll only be on a lot if it doesn't get up to temperature because there are too many rads, so it won't be at max temp!

 

[corgiman]

Actually Thats true.

 

[DP]

An option that can be exercised is to fit zone valves (if not already in place) and fit a programmer like Danfoss FP75 or a programmable roomstat. This will allow the heating to run with HW deactivated. HW can be programmed to come on say at 4.00 am, off at 6.30 am. Heating on at 6.30 to 8.30 etc. This would allow you to use the present boiler, would also upgrade the controls for future, ready for new boiler. Fit TRVs to shut off rads in rooms that are naturaly warm (heated due to south facing/ kitchen rad etc). If that is not enough, instal a third MV for bedrooms. A bit of an overkill but very energy efficient it is. It is the controls that make a system better.

 

[tomjones1234]

Thanks Chris, DP, very helpful indeed.

Excuse my ignorance but whats a zone valve and a MV? Getting to grips with the heating.

Cheers,
Tom

 

[D_Hailsham]

Pay a visit to Sedbuk and run their "Recommended Boiler Size" calculator. You may be surprised at the result.

I have a 4-bed detached house with its original 50,000BTU (15Kw) boiler. According to Sedbuk, this is about right. When I had cavity insulation installed I re-ran the Sedbuk calculator and it came up with 10kW.

How did you arrive at the figure of 65-70,000BTU? Calculated from scratch or just the size of the existing boiler plus the new rads?

I don't think you can make a boiler produce more heat than it is designed to. Presumably this is determined by the gas valve and the burner. So there is no way you can make the boiler "work harder"; though it might be on longer. Depends on whether it was correctly sized in the first place. [/url]

 

[JohnD]

I don't see that there's any prob with having rads which add up to more than the output of the boiler.

Mine add up to about 50% more than the boiler output, but most have TRVs on, and of course most of the time the external temperature is in the 5 to 15 degrees area, it is rarely below freezing, so there is not much heat loss and the house gets warm and the rads shut off as each room gets to temp.

Also disused rooms have the TRVs turned low so they put little load on the boiler.

If the house has been empty the big rads warm it up quickly.

Before I had the cavities filled the boiler had insufficient power to bring the house to temp on cold frosty nights. It just ran all the time.

You can't really overload a boiler as far as I can see. It just delivers heat, like a tap delivers water into a bath. If the bath is leaky, it may never fill up, but the tap doesn't know that.

I am not a heating engineer.

 

[tomjones1234]

Hi all,

The sizing was done by the heating engineer who came out to assess the current status of the radiators. I can see the benefit of TRV's for sure but am still curious that the boiler will be on most of the time.

It also appears that we might not have cavity wall insulation, am getting this checked. Is there an easy way to tell?

 

[D_Hailsham]

The sizing was done by the heating engineer who came out to assess the current status of the radiators.

It also appears that we might not have cavity wall insulation, am getting this checked. Is there an easy way to tell?

You may be able to see where the installers drilled through the brickwork and then filled in with cement. Look at the pointing at the joints in the brickwork for changes in colour. Alternatively, if you have access to the loft, shine a torch down the cavity and have a look. The insulation should come up almost to the top of the cavity.

If you have not done so, use the Sedbuk website I mentioned earlier to check the size of boiler you should have.

If you don't know if you have cavity insulation, the "heating engineer" will not have been able to accurately calculate the size of radiator All he has done is make a guess, based on "experience", which is based on previous guesses and so on.

 

[bengasman]

Sizing is based on averages, allowances and a fair bit of guesses chucked in for good measure. Make sure you run dhw and ch at separate times. It may take a bit longer to warm the house when it is really cold, but those days are few over the year. Being on more hours per day will not kill your boiler any time soon. No need to spend a lot of money for what might happen. Global warming should take care of the problem anyway, just drive your car a bit more to speed up this process

 

[Agile]

There are two aspects to calculating the heat output of the rads !

There is the heat output required to keep the house at 21°C when its -1°C outside. For an average three bed semi thats usually about 10-12kW.

Then there is the output of all the rads added together. That might be more or less than the heat actually needed by the house.

The boiler will actually last longer if its running 24/7 as that eliminates thermal cycling and corrosion problems.

It does no harm if too many rads or two few rads are added to the boiler as it will look after itself.

Tony