Gas Boiler w/ lower BTU output than total rads + hot water

Domicio · 23-01-2022 3:03pm #1

Hi guys, we are looking a house to buy and we just realized that the gas system boiler is 18w while the total rads and hot water tank would be consuming about 19w when running all together.

The owners mentioned that as the house is 3-zoned, they never run all together and they keep a couple of rads constantly closed as they don't used all rooms.

Questions:

1) Do you guys see any problem with it?

2) What would be the problem of running a CH system that needs more output than what the current boiler can deliver?

John.G · 24-01-2022 1:17pm

No, no problem.
Except that you are increasing the CH demand by more than say 25/30% still no problem IMO, the only problem would be in the morning if you are trying to heat up all three zones together, but you can heat say 2 zones and when up to temperature, heat the remaining zone. The main thing to watch is the HW cylinder as some of these have 10kw to 20kw coils for rapid heat up so just time the HW heating to come on for say 2 hrs in the morning before (central) heating required.

Domicio · 25-01-2022 9:35am

https://www.boards.ie/discussion/comment/118525098#Comment_118525098

Thanks a million!!

youtheman · 27-01-2022 8:35am

Remember that the heat requirement for a radiator and/or cylinder depends of the 'temperature difference', i.e. the difference in temperature between the water in the system and the surrounding system (room or water inside cylinder). So as the water in the cylinder heats up then the 'heat requirement' for the cylinder reduces accordingly. Same with radiators. So I'd be very wary of just adding up the 'quoted heat requirements' for you radiators and cylinder and comparing it with the output from your boiler.

Domicio · 27-01-2022 12:11pm

https://www.boards.ie/discussion/comment/118538709#Comment_118538709

May I ask how would you calculate it?

Let's say the heat requirement is higher than what the gas boiler can delivery, what would be the downside? Am I right to say the water is not going to get warm enough and there is no damage to the gas boiler?

cruizer101 · 27-01-2022 12:28pm

https://www.buildingservicesindex.co.uk/entry/136540/AEL-Heating-Solutions-Ltd/How-to-calculate-the-delta-T-for-a-radiator/

There is a table there with correction factors for different temperature differences.

That said I think you might overthinking it a bit. How did you determine the heat output of the rads? Measure them all?

The heat requirement of the room is kind of more important that the rad output.

Gas Boiler w/ lower BTU output than total rads + hot water

Comments