Why does a room at 19 degs feel colder on a cold dark night?

[adam2]

I have now rectified various faults in my neighbours central heating.

Boiler stat was set to only 60 degrees. Turned up to 75 degrees.
8 radiators air locked and needed bleeding.
Zone valve for main living room stuck shut, freed.
limited heating of fresh air supply, found one heating coil isolated due to leak, replacement ordered.

By normal guidelines, the new boiler is undersized for a house this big, however with good insulation and supplemented by a wood burning stove it should be fine. 24Kw boiler, suggested size for property is 40Kw.

[vtsnowedin]

I just came down from flushing out two lines of radiant floor heating in my daughters house. It is about ten years old and some of the "automatic" systems are not as automatic as they once were. The auto air release is letting lines get air locked and the auto boiler fill does not seem to function properly. It is set up with good garden hose connections on the return lines though so it is a simple task to open the return line while feeding new water into the boiler and flush until hot water returns.
Do those guidelines for heating unit size just go by floor area or are they more sophisticated to take in wall area and R factor plus window area and type of glazing?

[adam2]

The guidelines to which I refer are based on the following factors.

Plan area.
External wall area.
Single glazed window area, double glazed window area.
Any non-heated porches, conservatories, garages, sun rooms or the like.
Any other heating.
Insulation standards.
Location, what part of the UK.
Location, exposed or sheltered.
Design internal temperature.
Property permanently occupied or not.
Type of occupancy, owner occupied, rental, or holiday rental.

And possibly other factors.

[vtsnowedin]

Well that should give you a pretty good size estimate but of course you only need all of it on the coldest days of the year. Can the wood stove put out the equivalent of 16KW?

[woodburner]

A 40kW boiler is specified for extreme conditions, this means it is over rated for all but possibly two weeks in the year, usually around February. A more sensible approach is to have a lower rated boiler, eg 24kW, and use supplementary heating for the short periods when needed, or put on more clothes, either on the house (insulation) or the people (woolly jumpers and thermals).

[adam2]

Well that should give you a pretty good size estimate but of course you only need all of it on the coldest days of the year. Can the wood stove put out the equivalent of 16KW?

No, the wood stove is rated at 8Kw. Ample for a single very large room.

[adam2]

A 40kW boiler is specified for extreme conditions, this means it is over rated for all but possibly two weeks in the year, usually around February. A more sensible approach is to have a lower rated boiler, eg 24kW, and use supplementary heating for the short periods when needed, or put on more clothes, either on the house (insulation) or the people (woolly jumpers and thermals).

Yes, the smaller boiler now fitted should prove ample, especially as my new neighbours are realistic about wearing winter clothes and using warm bedding in the winter.
The exact degree of thermal insulation is unknown, but looks good.
Use of the stove in severe weather will also reduce boiler demand.

A room thermostat is placed at high level near the stove, when this detects that the stove is hot it operates a zone valve to isolate the central heating to the large living room.
This is set to 30 degrees at present but can be altered as needed.

The 30 degrees is NOT room temperature but is the temperature just below ceiling level and near the stove.

[vtsnowedin]

I'm not sure that high thermostat placement is needed. If the stove is doing it's job and has the room at mid wall level where the thermostats are usually located at 22 degrees or more then they would not call for any more heat from the boiler. That the ceiling temp is higher is a given but the mid level temp is the goal so why not measure that?

[kenneal - lagger]

..........
The exact degree of thermal insulation is unknown, but looks good. ............

From your description of the wall construction, Adam, the U value of the wall would appear to be in the region of 0.6 to 0.5, which is what a house of that era would have been built to, whereas the Building Regulations now require 0.2 and a PassivHaus would achieve in the region of 0.1 W/m2/degC. So not very well insulated.

[adam2]

..........
The exact degree of thermal insulation is unknown, but looks good. ............

From your description of the wall construction, Adam, the U value of the wall would appear to be in the region of 0.6 to 0.5, which is what a house of that era would have been built to, whereas the Building Regulations now require 0.2 and a PassivHaus would achieve in the region of 0.1 W/m2/degC. So not very well insulated.

Perhaps not, however the apparently undersized boiler is not only coping well, but is only running for about 20 to 25 minutes in each hour, averaged over the day.
After much tinkering with thermostatic radiator controls, temperatures are now a fairly consistent 23 degrees in the living room and 20 degrees elsewhere, apart from unused rooms which are 12 degrees.
As the premises already has central forced air ventilation, a heat pump might be worth considering.
Or perhaps solar thermal collectors to warm the incoming air.

[kenneal - lagger]

Introducing a heat exchanger into the outgoing airflow which then feeds warmed air into the ventilation unit would be the way to go. That would transfer up to 90% of the heat from the outgoing air into the incoming air. Unless the heat loss from the house is exceptionally low using the ventilation air to heat the house results in an uncomfortably hot, dry airflow which is why all the old air based heating systems have been replaced. PassivHauses use heat air but their heating requirement is exceptionally low.

[adam2]

An air to air heat exchanger was considered but rejected because there are several extract fans, none of them near the fresh air fan.

All toilets, bathrooms, cooking areas, and the smoking room* have local extract fans.

The fresh air is supplied to all bedrooms and living areas. It is only moderately heated and is not the main heat source. In winter it may heated to between 15 degrees and 25 degrees.
In summer it may be chilled to between 10 degrees and 20 degrees.
The two cooling units are each rated at 5KW of cooling capacity, with an electrical input of about 1.5Kw.
The two heating coils each provide several Kw of heating, the exact figure depending on the boiler temperature.
*Not seen a smoking room before in a newish house, It is a small area separated from the living room by glazed walls and a glass door. Equipped with furniture, lighters, ashtrays, and an automatic extract fan.

[kenneal - lagger]

....... and the smoking room* have local extract fans. .....

Were the walls painted brown or have they just turned brown with use? I remember the "old days" when smoking was more common when pub walls would all the the same hue as would the houses of heavy smokers. If it was painted over the stain would work its way through. Thank goodness for the smoking ban.

[adam2]

No, the smoking room has two glass walls and the other two are painted white.
I understand that the wife of the previous owner insisted on the new house incorporating a smoking room as her husband smoked a lot and She detested the habit.
The extract fan is controlled by a presence detector and runs for a few minutes after the last detection.
No one in the household of the new owners smokes, but a smoking room is handy to have for visitors who wish to partake without going outside in the rain.
Also useful for private telephone calls, since it is somewhat sound insulated. A telephone is installed.

[adam2]

The neighbours oil central heating is now working correctly and has given satisfaction in the recent cold spell.
The boiler only runs for an average of 30 minutes in each hour, during the cold weather, less in mild weather, suggesting that it is of ample capacity.

The subjective impression if walking around is of pleasant warmth without any excessive heating.