Thermostatic Valves, Condensing Boiler & Room Stat?

colinryan

Hi,

I'm in an old house about 18 months and since moving in have replaced the old boiler with a condensing one. All the rads (bar one) have thermostatic valves (TRVs) fitted. The house is all one zone right now (no motorised valves).

Our boiler currently is timed to run for twice daily for 2 hours. I have tuned the TRVs in each of the rooms (warmer downstairs in living area and cooler upstairs etc.) for 'average' winter temperatures. We then manually run the boiler if more heat is needed (which it frquently is) and often forget to turn it off.

One problem we have is that in the really cold weather (until we sort our insulation out) even if we leave the boiler running the house does not warm up sufficiently. This has led to bad habits of leaving the boiler on for long periods...

Our gas bills are quite high (the house is not as well insulated as it could be but working on this) and I have a few questions:

- In the current setup our boiler is constantly 'running' for the programmed on time. Am I right in saying that some of this time it is firing and other times it is just operating the pump (once the water reaches the target 70 degrees)?

- Assuming the above, is this efficient or should I be aiming to minimise pump running time once the house is warm?

- Should I consider installing a room thermostat so that the boiler shuts down once the right temperature is reached? I understand I need to but the room stat in the room where no TRVs are installed. I am presuming this would go some way to reduce the cost of leaving the boiler running manualy.

Basically - should I bother with a room stat (which is cheap in fairness) or just focus on insulating (no smart answers please).

Thanks,

C.

items

Well Colin, Once boiler is happy with heat in heat exchanger gas burner will shut down while circulation remains, boiler will sense heat a number of different ways depending on manufacture, some work off flow sensors other work from return temperature and some work off combined. The duration of burner time all depends on heat setting and how much heat loss you might have after boiler.

TRV's are a bit of a let down to be honest, thats how I see it. Having a room stat or two placed in ideal areas work best, even splitting heating into zones working of individual zone stats works out more economical than a TRV only type system.

From the sounds of things your rads could be undersized, if boilers running flat out yet rooms don't come up to temperature than all points to undersized rads.

I'm not sure how or who sized up heating system / heat loss requirements. Maybe you told plumber you intended on upgrading insulation and plumber based heat loss calculations working off house with upgraded insulation, if plumber hasn't then plumber should have worked out a heat loss / KW requirement base on house as it stands. If you can try and contact plumber and ask what he / she based calculations on, just thinking worst case, you might upgrade insulation and still suffer from an undersized system, it does happen so one to look into.

Gas boiler works hardiest off a cold system, if your only running 2 times for two hours, depending on gap between each hour you could be running boiler twice daily from coldest water. You might see an improvement if you lower boiler temperature and let it run on a bit longer, space out more over each day, try running 3 times. Its best to maintain some level of heat in heating pipe work, not roasting hot, just enough heat to lessen boiler work.

Old block houses left idol for weeks / months / years take some time to warm up to lived in feeling, maybe house had been idol before you moved in? We've had a very cold winter so far so its all against you at the moment.

Before installing stats / modifying heating best insulate as much as possible, insulation first.

Joey the lips

Insulation is the cheapest and most efficent way to improve the heat in any house.There was a chap with me from halo las week and he said 450,, of insulation.Which is 3 layers of fibreglass. Most people would not be as methodical about the trv planning and as items said the hardest house to heat is a cold house.

colinryan

Thanks for this.


I understand the point re insulation and have done all the easy stuff (roof cavity/drafts etc). The problem is the next step gets more expensive. Its a period red brick and some of the rear extension construction is cavity block so we are restricted in terms of external and blown insulation. I have been using Kingspan slabs internally as we do up rooms and we are looking at windows. So I will continue to work on insulation but it wont be overnight...

Hence I am also looking at heating and what to do next from an economical point of view... the TRVs were there when we moved in with the older boiler.

I suspect Rad size is a problem (two old ones were replaced when we upgraded the boiler). They are smaller but are double panels. To be honest I dont think the plumber put enough design thought into the system beyond boiler capacity (its big enough). I think I might look into some bigger rads.

One other point: Its a gravity fed system (non return valve fed from tank in attic on 2nd floor) and the pressure is just over 1 bar when running, I'm not sure what I can do to increase this but am I right in saying that a higher pressure would increase the efficiency of the boiler?

Am I right in saying though that a Thermostat is still a good idea i.e. would compliment the system? Its cheap to add ....


C.

eoghan.geraghty

A thermostat will not help you here because as you say the house is not getting warm enough, so a thermostat would be redundant.
Was the system power flushed when the boiler was changed?
A proper flushing of the system would help any older rads work more effectively.
Have a look at insulating all the heating pipes under floorboards with the grey sleeving insulation ( armaflex?) as this will help all the available heat get to the rads.
What size thermal liner board have you used in the rooms you've done already?

colinryan

Hi,

System was flushed and inhibitor added. I have bled all rads and topped up system a few times to make sure not sludgy etc.;. Top floor rads took a bit of fiddling as pressure was not sufficient to quickly force the air out - 3 storey house and gravity fed system. Top up tank is only 1.5 meters higher than higest rad (over 5 metres higher than boiler return).

The wall insulation fitted to exterior walls (inside) is 30mm backed kingspan (I cant go thicker as I am trying to preserve original plater coving and any more will sit proud of this).

I have insulated all visible pipes but will revisit those I can get access to.

A few questions re rads:
- What are best type - I have read that 2 panel or best (i.e. 3 panel does not add much more efficiency)
- The previous owner had painted some of the older rads with matt emulsion (wall paint) - does this inhibit heat transfer
- How do I calculate ideal rad size/capacity for rooms/house?


Is ther any way to increase the pressure in a gravity fed system or should I consider sealing it to increase the pressure?

youtheman

Your system is 'gravity fed', or sometimes called 'vented' or sometimes called 'open'. The pressure is governed by the height of the header tank in the attic.

If you want to make it a pressurised system then you have to make sure your boiler is designed so, but the most important thing is that you are increasing the pressure rating of your network of pipes. They recommend you 'pressure test' it to 3 bar (I think). But the major risk is that you may cause a leak by the very act of pressure testing the pipework (i.e create a leak that was not there before). Then you have a major problem.

My system is vented, when I installed a new condensing boiler I considered the risk of increasing the pressure to be too high. So I left it vented.

My understanding is that a pressurised system is not more efficient than a vented system, but the main advantage is that the system heats up in a more uniform way (feel free to correct me though)

sweetie

some very informative stuff there guys. cheers

items

colinryan wrote: »

Hi,

System was flushed and inhibitor added. I have bled all rads and topped up system a few times to make sure not sludgy etc.;. Top floor rads took a bit of fiddling as pressure was not sufficient to quickly force the air out - 3 storey house and gravity fed system. Top up tank is only 1.5 meters higher than higest rad (over 5 metres higher than boiler return).

The wall insulation fitted to exterior walls (inside) is 30mm backed kingspan (I cant go thicker as I am trying to preserve original plater coving and any more will sit proud of this).

I have insulated all visible pipes but will revisit those I can get access to.

A few questions re rads:
- What are best type - I have read that 2 panel or best (i.e. 3 panel does not add much more efficiency)
- The previous owner had painted some of the older rads with matt emulsion (wall paint) - does this inhibit heat transfer
- How do I calculate ideal rad size/capacity for rooms/house?


Is ther any way to increase the pressure in a gravity fed system or should I consider sealing it to increase the pressure?

All roll top rads are pretty much the same, rad output depends on rad size, no real output difference in double / single panel except for price. A 500 double might cost 120 euro, a 1000 single might only cost 90 euro, both rads will have more or less same output. Doubles tend to be used when having difficulty locating a single, or when a room requires two rads, its much neater to use just a double so all depends on your room layout.

Anything on or in front of rad can effect convection, paint on rad will effect output but not a noticeable difference, I doubt taking paint off rad will make a huge improvement.

To install a heating system you have to calculate house heat loss, a special formula is used and all sorts of different things are factored into the calculation, type of room, room size and height, type of floor, type of ceiling, how many external walls, type of walls, windows, doors, how many air changes per hour, lowest outside temperature (-2), hot water requirement (cylinder), boiler efficiency, thats just to name a few. I have a special heat loss calculator, all I have to do is turn a few wheels matching size of room, type of walls etc and once everything is lined up, calculator gives figure. If you have a look online their might be something available, some kind of heat loss program you can download. You have to gain some knowledge in house building material U valve, windows and walls, floors, insulation etc all have a U Value (heat loss).

Water under pressure tends to heat better, almost easier, your condensing boiler is set to run best from a recommended system pressure, have a look at your boiler manual for recommended system pressure.

You should look into sealing system by installing an expansion vessel and system fill directly from mains water via dedicated mains filing loop. In this day and age, no real need to have an open system, might be a case where you have a back boiler, thats the only real reason to keep an open vented system, even with a back boiler heating system can be separated leaving back boiler open, condensing boiler sealed.

colinryan

Thanks for the detailed reply.

And can I get your thoughts on the room thermostat - no point I'm guessing?

items

Not sure what you mean by thoughts on room stat?

Best heating systems out their work of zones, two story split into up's and downs along with hot water. Bungalow depending on lay out can be split between living / rec areas and bedrooms.

In both cases when towel rads are fitted in bathrooms its best to keep towel rads with cylinder circuit, that way during summer when rads are off, towel rads will still heat up along with hot water, towel rads don't have a great output, in some cases an additional rad should be installed per heat loss calculation, additional rad becomes part of living / bed room circuit.

All zones are controlled by MVs (motorized on/off valve) MV's are controlled by room stats and cylinder stat. Boiler is then controlled by time clock, should all stats become satisfied while boiler is running for programed time a heating by pass must be fitted, normally @ hot press, its nothing major just connecting flow and return together with a valve inbetween to restrict flow from going into return to much. When all MV's are closed boiler will only circulate through by pass then soon after boiler burner will stop firing as boiler temp will be quickly reached. Boiler might tip on and off for the duration of timed progame as required by room stats.

The above is just basic, more advanced options are availabe, by using 3 channel time clock with multiple programs for calling boiler on for different zones individually, you can also purchase multi channel time clocks with build in thermostats.

Fitting stat in correct location is the key, back in the day stats were wired to halls and landings as they where coldest area. House's had poor insulation so stats had to be fitted in coldest locations to allow other rooms to heat above coldest areas.

Times are different now, insulation has improved so for an efficent system best locate stats in acutall areas of use, if you had two stats for living / sleeping its better to locate living stat in living room away from opening doors and windows, fire places etc and for sleeping best locate stat in bedroom again away from opening doors and windows.

This way heating system will work from the actual heat you feel and program to suit instead of wide open halls and landings.

I've wrote out pretty much how stats work so gives you an idea on what to look into while your improving system.

You mentioned you had a stat in a room where rad had no TRV, moving stat to another location wont really help things that much, TRV's are more or less rad valves, they might limit flow to a lesser amout but not having one wont make any real difference than installing a stat where their is a TRV fitted.

Many houses have combined TRV along with room stats, and many have just standard rad valves along with room stats, I cant tell the difference between the two and I've never noticed any difference in Oil / Gas bills. To me both TRV and Standard Rad valve are the same, I've no idea why Government brought out a Grant to improve heating by adding TRV's, would of made a lot more sense to put money towards system clean and inhibit, that way people would be more aware of how to run heating properly. All boilers manufactures recommend adding inhibitor, for some its a requirement under warranty but still seldom add inhibitor.