Hi Chris, what Jody is speaking about is the relationship of Boiler/System water temperature and condensing operational efficiency. His example is based on a high temperature heat emitter system design. There are many variables which either enhance or limit the correct settings and reflected efficiency. The pumps, distribution piping, system Delta T and specifically, and the heat emitter design type and the location of the installation (Every location will have different weather data. Jody’s example is based on the Boston MA area), are all contributing factors to setting correct control parameters. If we were talking about Edmonton Alberta the design outdoor temp would be -29F instead of 0F, if we look at Vancouver BC design outdoor temp is 16F. If we look at heat emitter design, a high mass radiant floor system, (low temperature design), will be based on a design water temperature of 120F instead of 180F. The operation of the thermostat does not necessarily have much effect on the efficiency. That said, if the zone thermostats start and stop the boiler, as opposed to only operating pumps or zone valves, this can affect efficiency. (See other videos on our You Tube channel titled “Why your thermostat is like your car keys” and “Using thermostats with modulating boilers). These videos explain why every time you start and stop a modulating, condensing boiler it will have a direct effect on the “seasonal” efficiency because of the number of boiler cycles in a season. These videos were based on the previous Vitotronic control generation, but the principles are the same for the new boiler control platform on your boiler.

The challenges with converting older gravity systems to forced circulation are numerous. The piping is much larger because the water needed to move through the system by the buoyancy of hotter water with minimal pipe resistance. However, that drastically increases the mass of water in the system. Plus the piping is usually not very well insulated if at all. Once you add a pump and start moving water mechanically, this changes a lot of the thermal dynamics. If you start and stop the pump and or the boiler by a thermostat, when the thermostat closes you need to reheat a lot of water, which slows the recovery time and leads to larger temperature swings in the space. If you run the pump continuously, the heat loss may be significant because of the mass of water in uninsulated pipes. The CU3A boiler does not require a pump to be running to run the burner and keep the water in the boiler at set point. The 13-18 USG in the boiler will be ready to go make heat. However, this may be a lot less than the mass of water in the piping system. It really is a site-specific choice if it’s better to run the pump continuously in a converted gravity system but the CU3A boiler will work in both cases.

@@marknorris9722 Thank you Mark!

@@marknorris9722 Mark, do you know when the updated CU3A is going to hit the market? I was watching a video on the new Vitodens 100 with the nicer display, and they said the CU3A is also getting an update soon.

@@Shahrdad I do not have a date for this.

Care to elaborate? I am considering a Viessmann next.

@@fearone9694 My Viessmann doesn't.... 1. work properly with a cold return (turns the burner off) 2. offer 2 temperatures - one for heating, one for hot water 3. pumps heat OUT of the house via the flue. They're one of the better boilers but that doesn't mean they're a good/efficient boiler. Rather than considering a new boiler, spend your money on insulating and draught-proofing (sealing up) your home. Fit extra external doors - so when a door is open, a second door prevents fresh cold air blowing in. Change your heating from radiators to a ventilation system with heat pumps - fresh air is good for you and the heat pumps will keep the heat in the property but change the air ! Look at solar panels and wind for sources of electricity.