heating kw required

moan 77

Hi all,

I am building a 250 sq meter 1.5 story domer, 130 sq meter ground floor the rest first floor underfloor heating on both hopping to have 300 liter hot water storage of domestic use. does any one know how mush kw this requires, going to use a heatpump but could use oil burner.

any help would be great, thanking you all in advance.

sinnerboy

IF - you build reasonably well - i.e. to min b regs insulations and air tightness standards - 50w/m2 i.e. 12.5 KW boiler or heat pump

In context - PH standard of 10w/m2 = 2.5 KW

Thats for space Heating alone . You need to add on for DHW

PeteHeat

Hi,

Fairly close to sinnerboy, I would be recommending 60w per m2 = 15 Kw

Where I may be different is I would also recommend the back up system of oil, gas or pellet (bivalent system).

The reason being heat pumps especially air > water are tested based on the temperatures they are expected to achieve with the temperature of the air used to recharge.

There were a lot of shocks this year with the prolonged cold snap, systems that had worked well in the past were not able to cope with the very low temperatures.

We have one enquiry to correct a ground source system that ran so cold the garden looks like it was ploughed, the system caused frost heave because the pipes are not deep enough to recharge, the same system is six years old and this year was the first visible sign there was a problem.

The 300 litre cylinder will play havoc with your COP if it's depending on the heat pump because your UFH will be happy with a flow temp approx 35c but the cylinder needs to achieve 50c for general use and over 60c once a week to prevent legionella.

.

moan 77

cheers lads,
i understand what your saying. any idea roughly what the full kw would be if 15 kw is the space heating what extra would be needed for the hot water for washing the 5 bodies living in the house would i be up around 20 kw.

sinnerboy

Yes thats about right

http://www.diydata.com/planning/ch_design/hot_water.php

.