Comments by "eDoc2020" (@eDoc2020) on "Old HVAC industry practices are holding us back and costing us money. But we can fix it." video.

Hydronic systems are also an option. Have one central compressor heating/cooling a loop of water which goes to simple fan coil units. The thermal mass of the water means the compressor can cycle less often during low load situations. A water loop also enables in-floor heating which is usually more efficient.
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@rafflesmaos If you have fan coils and in-floor heat you could configure it so the fan units are always contributing. That would mostly eliminate thermal lag. But I also need to ask, wouldn't insulation between the slab and the floor also eliminate this lag? Having said all this I would probably also have a small ducted system for air circulation and HRV/ERV.
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With a smaller system you wouldn't need as much airflow. This results in much quieter air ducts.
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If your radiators don't put out enough heat with low temperature water you can add a fan to them. In the US the term for this is a fan coil unit (FCU). A fan blowing through an existing radiator would also work.
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@asbestosfibers1325 The raw equipment doesn't cost much more but that's before any dealer markups. And regarding that $10, it's probably a little bit more, especially since you're probably switching from a 17" to a 21" cabinet. Probably more like 100-300 USD.
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If you're concerned about resale value you shouldn't be. Practically nobody checks heating capacity when buying a house. Even if the system were actually undersized they won't know as long as it's warm during the tour. But a 74F design temperature is fine; I believe the actual standard is 70. And there's still the heat strips available which nearly double the total available heating capacity. Maybe it would be worth going from a 2 ton to a 2.5 ton.
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@jmr5125 In that case the inspectors are part of the problem. And ideally the sell sheet for the house should include an estimate of HVAC running costs because it can be such a large expense.
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@rafflesmaos I understand how the water would continue emitting heat but how would a slab under an insulated floor emit heat?
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@Science1144 Not quite. When the indoor temperature is set back lower than the design temperature your heat losses are lower than expected. This means the 100% sized furnace still has some extra power to bring the temperature back up even on the coldest day. And on the other 362 days it can do this without struggling. And this effect is even greater with heat pumps. Heat pumps actually output more than their designed output when the indoor temperature is low. Having said that, it's fine (and I'd argue a good idea) to oversize a little bit, perhaps 15-25%. This can also provide insurance for possible changes in the building's performance. Up to 150% sizing generally doesn't hurt performance. If the installed equipment is over twice as large as the calculated worst case there better be a very good reason.
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Did you watch to the end of the video? Despite the temperature differences Alec determined that his heating load and cooling loads are very similar.
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@jackdunagan331 I'm pretty sure the short cycling caused by an oversized unit is much more stressful than running 100% for 12 hours a few times a year. I've read that up to 50% over-sizing has minimal side effects so perhaps Alec's parents could have gone with a 4t instead of a 3t unit. 5 tons would definitely be too much.
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@jackdunagan331 I imagine variable speed inverter units have the greatest physical longevity. Running at half speed all the time needs to be less wear than running at full speed half the time. But really, is it worth worrying about the compressor? I've never seen a dead HVACR compressor but leaks in the coil seem more common.
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Mini-splits usually run the indoor unit from the outdoor unit. Central ducted systems usually have a separate feed to the AHU and have low-voltage wiring connecting the two. Even if you do need new wiring just run it alongside the refrigerant linesets.
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COP shouldn't be in your calculations. Heat pumps are sold on on output power, not input power.
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There's another way to determine your actual heating requirements without needing a smart thermostat: look at the gas meter/bill. Most of it will go to the heating system (and the rest heats the house indirectly) so divide by your furnace efficiency to get the actual heat output into the home. The gas bills around here show average gas usage per day as well as average outdoor temperature during the billing period so it's easy to do the math.
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You don't need a smart meter, just read it manually. Or even easier, wait for your bill. The gas bills around here show average daily usage in therms (which can easily be converted to Btu/hr ow kWh) as well as the average outdoor temperature over the billing period.
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The same principles apply to boiler systems.
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