add ANOTHER baseboard to monoflo tee?

[000utback]

I have 3 main heating zones/pumps in my old house; oil water heater at approx 180F. Let's talk about one zone. 1-1/4 Cu pipe with Monoflo tees. He services 6' baseboard, 4' baseboard, 8' baseboard, cast iron radiator, 7' baseboard. Each of those is on his own tee set, using 3/4 Cu and/or Pex.
The PO left an open set of tees to supply a future room (sunroom). I put an 8' and 10' baseboard in series fed from the one tee set, plus the pex tubing to run 18' from the tees to heaters. - twice as far as the other heaters.
The good news is that the inlet temperature for the sunroom is the same as all the other heaters, indicating that the monoflo tees are still diverting plenty of water, in spite of the greater distance and 2 rads in series. I checked that with an FLIR viewer after starting the furnace on a cold day. All the heaters had very similar heat rise.
Query now, is that the sunroom still doesn't get enough heat. I would like to add another 4' baseboard in series. This doesn't have much impact on total length, since it really means that I'm poking the return line up, through the heater, then back down, so the increase in back pressure is only 4 elbows and a couple feet up/down. My concern is at what point I create too much resistance and get less water off the tee, thus negating what I did by adding another heater.
Cutting in to the main pipe and adding another set of tees, and doing another 3/4 run to the heater, is a lot of work and expense.
Do ya'll think that adding the 4' section will hurt my flow much?
thanks for any advice. I appreciate all that I have learned on this forum.
- White Cloud

 

[Dana]

The heat loss/gain characteristics to sunrooms are dramatically different from other rooms, and not a great candidate for zoning in common with other rooms, since it'll never balance. At night it's a much lossier room, and during days there's often more solar gain than the room actually needs, even when other rooms still need the heat.

Control flow to the sunroom with it's own set of thermostatically zone valves right at that loop rather than trying to get it to temperature balance with other rooms using monoflow tees. A branch bypassing the sunroom radiation completely that is closed (or nearly closed to all flow when the sunroom is calling for heat, and completely open when the sunroom isn't calling for heat , with flow to that radiation stopped when in that state would work. The call for heat from the is still from the major zone, but local zone valving makes the sunroom a micro-zone within that zone.

 

[Sponsor]

 

[000utback]

Dana, thanks for the advice. You're right on the difficulty in controlling a different room with radically different conditions. My initial thinking was that furnace would have to run till the sunroom was satisfied, and the other 4 rooms on the same zone would use their manual or mechanical automatic controls (t'stat valve on radiator and some baseboard, mechanical vane on baseboard) to balance the heat output. But your suggestion would allow proportionally much more heat (or less on sunny afternoons) into the sunroom for the same amount of run time.

To pursue your suggestion, I would need to add an ambient air t'stat in the sunroom controlling the 3-way valve in the circulating loop. Does that need to be modulating, or simply open/shut? If your familiar enough to suggest specific models, that's very helpful.

 

[000utback]

Actually, I could accomplish what you're saying by replacing the monoflo Ts with conventional Ts, and adding a 1-1/4 valve in the 1-1/4 line BETWEEN the 2 Ts. But since the 3/4 leg can't handle all the water from the 1-1/4 loop, I need to either control the valve to assure it doesn't totally close, or drill a sufficient sized hole through the closed valve to allow some water to stay in the loop.