I'm installing 16' of new baseboard hw in an on slab addition where my primary heat source has been a coal stove. I'm considering tying into a nearby loop off zone 1 that heats the kitchen and very seldom used dining room. I will continue to use the coal stove as a supplemental heat source... but when I have the coal stove on I would like to valve off (thermostatically) hw flow from the loop to this addition. Would a TRV with a remote temperature sensor be a good option for this application? I think I'd like to stay away from adding a new zone since, to conserve fuel oil, I only want to heat the boiler when zone 1 calls for heat... does this make sense?

 

If I understand what you are trying to accomplish, I think it would work, but:

You can't use a TRV on a SERIES loop connection because when the TRV closes, the entire loop shuts down. You can use a TRV with a two-pipe, or a diverter tee system.

 

I was planning on teeing off the existing loop and installing the TRV immediately after the tee- then continue my run into the addition and return by tying back into the original loop close to the tee. Does this describe the diverter tee system you suggest? Thanks Trooper.

 

If you use standard tees, you won't get much, if any, flow through the loop. There needs to be a pressure differential for there to be flow. With closely spaced standard tees, there will be very little pressure difference between them and the water will just continue on it's merry way straight down the pipe, never entering the heating loop.

In fact, even if you use the diverter tees, and the loop is long, you may not get much/any flow with a long-is heating loop.

Diverter tees (also called MONOFLO tees) have a 'venturi' built inside of them to create the pressure differential.

Check out this article for lots of info, Q & A style, easy reading.

Diverter Tee Info

You might just be better off with adding another zone ...

 

Thanks again Trooper for the info. I think I have a much better understanding of the diverter/MONOFLOW tee concept. You warn away from using these tees in long loops. I need to run out and return for a total of almost 60' do you think this too long a run? I will have two 8' baseboard radiators located just above the main. If this run is marginal should I consider MONOFLOW tees on both the supply and return sides? Also I hope there will be no problem going from the 1/2" branch of the MONOFLOW up to 3/4" baseboard...

 

Yes, you can use diverters on supply and return both, but 60' is an awful long loop for that. There is one q/a in that article that mentions "the width of the radiator apart" ... I think you need to consider the entire loop of piping as the radiator in this example, so how are you going to space those tees 60' apart on the main run ?

Also, I lied... you _can't_ use a TRV on a diverter tee system. Sorry, my fingers type faster than my brain thinks sometimes. When the TRV closes the loop, the extra friction in the main run with the loop side of the tees closed off will CHOKE the flow in the main run. Your other b/b's will suffer badly.

It really seems like the individual zone will be your best bet. If you can tap into zone 1 back at the boiler, you won't have to add hardware for the zone. Leave all that intact and tee off the supply and return at that point with 1/2", run it out to your room, with the TRV on the new bb. If you do this, then when zone 1 calls for heat, the boiler will run. If the TRV is calling for heat, you'll get it there too. If the TRV isn't calling, you will still get heat in zone 1.

In your application, with 16' of baseboard, you only need about 10,000 BTU to heat them, which translates to 1 GPM, which is fine to run 1/2" pipe and adapt to the 3/4" bb.

This is also a very good read:

Zoning Made Easy