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I've just purchased a 15-year old house heated with a gas boiler and multiple baseboard zones controlled with zone valves. The house is built to be energy efficient, and I have no doubt that there's plenty of capacity to maintain reasonable temperatures, but recovery times are very long (on the order of 1 hour/degree F at cooler temperatures). I've been told by our heating contractor that our boiler is oversized for the house; this correlates with my observation that the duty cycle of the flame is fairly low even during a long recovery, indicating that we are not extracting heat from the system as quickly as it can produce it.

We have two use cases for recovery - zones that aren't used daily, or only used part of the day (i.e., office), and when we are away from the house for days up to a few weeks. I'd like to focus on the kitchen/living room zone, for the "returning home" scenario. This part of the house has a good size run of baseboard in the dining area (approx 15-16'), a kick panel blower unit in the kitchen, and four in-floor blower units in the living room. There really isn't room to add any more baseboard capacity (except possibly a second run above the existing), so I'm looking at other options:

  • add an air handler in the basement or coat closet and configure it as a second stage (there's plenty of room for a modest unit, but supply and return ducting might be messy)
  • explore options to increase the capacity of the existing in-floor blower units (I have not investigated these at all yet)
  • explore increasing the operating temperature of the system (currently set for 160/180˚F; perhaps only on the low end
  • get used to it, and start the recovery earlier with remotely accessible thermostats

Are there other options that might make it possible to eke more out of the existing baseboard runs (i.e., fans)?

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    Are the fins clean? Are the flaps open? - I've seen quite a few people who don't realize that most hot-water baseboards have a control flap that can be open or closed, to regulate heat delivery. Similarly, if your fan-coil units are not clean, they will perform poorly. – Ecnerwal Jan 26 '20 at 23:18
  • The baseboard fins appear to be clean, and yes, the flaps are open. I haven't gone into the fan units yet, but will next trip there. It's probably worth pulling the cover off the baseboard and gently vacuuming the fins, any efficiency improvement would be welcome. – TomG Jan 27 '20 at 0:12
  • Do you have good hot water flow through the system? The biggest boiler in the world isn't going to help if the flow is constricted. – SteveSh Jan 28 '20 at 15:05
  • For how long of a period are you turning down your heat, and by how much? – SteveSh Jan 28 '20 at 15:06
  • @stevesh - I don't have any reason to suspect a flow issue, the baseboards come up to temperature very quickly when the zone valve opens. – TomG Jan 28 '20 at 18:37
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You could investigate adding additional baseboard heating units in each room either longer if there is room or double stacked units. You could adjust the boiler water temp to 190/200 to increase the heat output of the existing baseboard units. If this were my problem and I didn't know what to do I would call a professional and ask for recommendations. Knowing what to recommend from a statement made or question asked is difficult since no one can see the house, the floor plan, or the actual installed equipment. There may be a lot that can be done to help but actually being at your residence would allow for the best outcome. If you could, post pictures of your location, situation and the installed equipment for better suggestions

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  • Thanks. I expect we'll be calling in a pro, I'm looking for as much background as I can before doing so. – TomG Jan 28 '20 at 18:43
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I would check the heat output of the emitters. Suppose the house needs 50,000 BTU, and the boiler produces 100,000 BTU, but the baseboard only emits 35,000 BTU. Even if the boiler is producing plenty of heat the rooms won't get hot. If this is your problem then you would need to add additional emitters.

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