Turning off some radiators?

[sprinkler]

I heard that turning off some rads in a house is not a good idea. In this case there is a combi oil boiler (sealed room type), with about 13 rads, and a somewhat oversized boiler. Each rad has a seperate hot in pipe and a return pipe. (I think its called a two pipe system). Anyway is it true that it is better to leave all the rads on full, or is it ok to to reduce some of them with the manual valve (not thermostatic type), Thank you.

[hj]

IT really depends on whether you have a two pipe system, or a Mono-Flo single pipe one. A two pipe system does not depend on the water flowing through the radiator to maintain the flow/temperature downstream. A Mono-Flo system with valves shut off will degrade the entire system.

[sprinkler]

Yea...makes sense. BTW it is a two-pipe system. Just turned on the system for the first time today. Seems fine except that it takes the last rad (upstairs) quite a while to heat. Maybe because the connecting pipes to the last rad do a longish detour to the attic (with bleed valves in attic at highest point ) and back down to the next room? Is it advisable to "balance" the rads by partially closing the valves on the hottest rads, so getting heat more evenly circulated around the house? Because I heard that the thermostatic valves aren't great.Thanks.

[plumber1]

I've got to ask, is this a water or steam system?

[hj]

Closing valves on the hottest radiators does nothing to speed the heat to the other ones. It just slows down the rate of heating in that room so it does not become overheated, or turn off the thermostat if it is located in that room.

[sprinkler]

It's an oil combi burner, using water in a sealed system around the rads. I did hear something before about "balancing" rads and I thought it would be logical(?) that reducing the heat in the hottest rads (the ones nearest to the boiler) would mean that the further rads would get extra heat faster. Or is there some other trick for getting heat to the last rad more quickly?

[jadnashua]

I'm not a pro on this, but it very much depends on how well the pipes are layed out. If each radiator had an independent loop to a manifold to the boiler (unlikely) you could balance each branch based on the friction (head?) to each so they all got a balanced flow. But, I don't think they often do it that way. So, the radiator that is furthest, has the most friction, and the lower flow unless it is piped with larger pipe (again, which I doubt happened).

Even if you were to be able to adjust the flows through each individual radiator to maintain an eventual steady state temperature in each room (could take a long time), the ones furthest from the boiler would take longer to heat up because of the additional mass and losses along the way - the heat by the time it got there would be lower even if the flow was balanced. This would change based on the prevailing winds and sun exposure, so it would be tough to maintain without constant tweaking.

The only time I lived where I had radiators was in Europe...the thermostatic valves seemed to work. As you can tell, I don't have much experience.

[sprinkler]

The last 2 rads are on the same branch (15mm) from the main pipe (22mm), but for the last rad the pipes detour for about 12 meters up into the attic, across, down etc. to the last rad. I have bleed valves in the attic which are at the highest point, but only by a few cms or so. Do you think it might be worth raising the bleed valves by a meter or so, just in case some air might still be in the attic pipes? The branch flow pipe to the last rad gets hot(ish) but the return stays just slightly warm.

[jadnashua]

Is the pipe insulated in the attic? If there is flow and no leaks, eventually, all of the air should get extracted from the system. Do you have an expansion tank on the system? I would think that if you do not, then this would allow air to be introduced in the system...when the water cools and contracts, it will pull air into it from any marginal connection. Same problem with it when you are heating, if it has no place to expand, it will either raise the pressure higher than design, or will leak out under that pressure. An expansion tank allows that expansion/contraction to not impact the system pressure, and helps minimize leaks of both water and air.

[sprinkler]

yes there is an exànsion tank built into the combi (condenser) boiler which is situated down in a garage under the house. And there is insulation on the attic pipes. At first when the last rad was staying cold I lifted the attic pipes (they are lying on the attic floor) a couple of inches next to the bleed valves, and some air escaped from the higher automatic bleed valve. Then the last rad at least got a bit warm. Then today I opened the highest bleed valve until water came out and I think I also heard some more air escape, though I haven't tried the system since then. The bleed valves are mounted on tee joints just above level of the top pipes, but now I think I will raise them at least 2 or 3 inches higher to (hopefully?) get rid of any remaining air faster.

[jadnashua]

I have very little experience with bleed valves. One that was installed with my last boiler was a Spirovent. This thing has a SS brush that actually (or at least they say it does!) brushes out micro air bubbles. WHen they accumulate enough, it releases the air. It has seemed to work quite well. Don't know if there are others of similar design. It has a life-time warranty.