Sizing a boiler

Dave_4

Hello,
I am in the process of hiring a contractor to convert my gravity system to a closed system and replace my 80 year boiler with something a bit newer. I have done my own heat loss calculation (using Slantfin's software) and it comes out to be 50,000 BTU/hr on the coldest day of the year. Assuming my heat loss calc is correct, what size of boiler (net output) would you choose? How much margin do you build into your systems?

jim lockard

bmac

Have you measured the existing rads in your home? When sizing a replacment boiler, measuring the amount of raditon currently in your home and sizing the boiler to that load is often the best way to proceed.
You may also wish to take a look at outdoor reset and constant circulation for your gravity conversion. Best Wishes J.Lockard

Dave_4

I di do the EDR calculations of the rads - they total around 66000 BTU/hr at an avg temp of 170F.

BTW, I am strongly considering an outdoor reset.

Thanks.

Weezbo

it might help to consider the type of fuel you are having

available and perhaps letting others in on it...

that way it would be a shade easier to Help...

Guy Woollard

calcs

Setting the flow might be a bit tricky, as the gravity systems weren't routed in any linear fashion. The radiation is most likely slightly oversized to your home today, as there have most likely been improvements to windows/ doors/ insulation, etc that have dropped the actual losses from the original envelope. Staying in the 50K to 60K range should be fine.
The question that arises is if you are going to want domestic hot water from the new boiler. If your fuel is gas, then I would suggest a modulating boiler that will ramp up for domestic production in an indirect, yet only operate at that 55Kish for the heat.

Guy Woollard
N.E. Regional Sales Mgr
Triangle Tube Corp.

Dave_4

The fuel I will be using is gas. I am also considering adding an indirect DHW tank onto this boiler which will clearly require more output from the boiler. How much more?

I cannot put in a condensing boiler (the venting would have to occur on my neighbour's driveway) so I have to vent out the chimney. I am currently considering the Viessmann Vitogas 100 line.

Thanks again.

Unknown

Ever considered

using the existing chimney as a raceway?, then a condensing boiler should be no-prob.

Dave