Dual-fuel heat pump (was 'Multiple zones')

[WorthFlorida]

FYI, to get the most efficiency, the duct work needs to be large enough. HE units you want the air over coils longer to absorb the heat but fast enough to reach the furthest rooms. Your 20 year old home maybe OK, ask the contractor for his opinion. Usually you want the main trunk to be large enough before branching.

 

[Chevsky]

Fingers crossed, and hoping if anything I'll only need to improve the flex's that connect the floor registers. Calculate, or measure static pressure? Large space (2300sf) with planned 42Kbtu/3.5ton has three existing main runs 18x8, 12x8, 12x8 inside, each has 1-2 90°s. So ~2000 CFM before factoring fiberboard and bends? The return is only 24x8 but it's short (open concept house). Enough for HP heating? How does the duct calculation differ between furnace BTUs and HP BTUs? Is 400CFM/ton already sized for HP? I guess this weekend will be calculating room by room, duct by duct.

 

[Sponsor]

 

[Chevsky]

I think having two separate systems is better than sharing an outdoor compressor. If one breaks down you could be weeks away from relief. Especially with heat pump stuff. I think most people would rather have two systems as long as they are both effeciant you should be using the same amount of energy.

I like the "duel fuel" heat pump/furnace idea.

You said you had a fireplace but also would tear out your chimney? Are these two separate structures?

Among the many bullet-point-questions I'm compiling, this will be another:
Q: If a problem arises in the HP (loss of charge, say), will the inside unit(s) continue to work on furnace-mode/gas/propane, despite [being above] the change-over °F set-point?

Thanks for bringing this up.

Same structure, and the two systems share the same chimney. But no "easy" way to tie ducts together, except removing the chimney and using it's footprint, but then we'd still want that smaller space on a separate zone anyway due to infrequent use. So... at least this is a way to save on new HP equipment purchase, leverage the heat pump's multi-zone capabilites, shared BTU capacity, and existing duct work, without a major redesign of ducts. Water heater is also propane, and fairly new, and uses this same chimney... I'm trying to upgrade a bit at a time so i don't have to lay out lots $$$ all at one time.

 

[Chevsky]

I'll be interested in your outcome. Heat pump owners like saving money, but usually admit the house isn't very comfortable. Which can be fine, but I hate a cold house in the winter and blasting more hot dry air is generally makes me feel sick.

Yeah... I'm not excited about switching as far as "comfort" goes. I too like low airflow and hot air from the registers. The industry marketing "more comfort with HP" I regard as hooey (creepy images of a couple with their child, in a stark white living room, smiling). I expect "windy" and cool wind" (body temp is 98.6°F, so pushing lots of 85-90°F air is going to feel cooler, no way around that). I like to sleep with the temp turned down, but they insist not to do that due to the slow/hard recovery. Not to mention that pushing a much greater volume of air around COSTS $$ -- just the "work" in joules alone is less efficient than smaller puffs of warmer air, exactly when you want it. AND by pushing all that air around the house, it's increasing the conduction of heat to the outside (assuming a well-insulated ceiling, low air-leak, etc), tho I suppose it reduces the thermocline if high ceilings. Given that the new fans run at a slower/optimal speed, and the better SEER, etc., yes the system is much more efficient. But there's no denying some compromises coupled to reducing dependence on fossil fuel and having a smaller carbon footprint. Oh well.

 

[Fitter30]

Fingers crossed, and hoping if anything I'll only need to improve the flex's that connect the floor registers. Calculate, or measure static pressure? Large space (2300sf) with planned 42Kbtu/3.5ton has three existing main runs 18x8, 12x8, 12x8 inside, each has 1-2 90°s. So ~2000 CFM before factoring fiberboard and bends? The return is only 24x8 but it's short (open concept house). Enough for HP heating? How does the duct calculation differ between furnace BTUs and HP BTUs? Is 400CFM/ton already sized for HP? I guess this weekend will be calculating room by room, duct by duct.

Have to do something with the return need at least 320 sq inchs 1600cfm
24x8 =192 put a grill on it probably choking it off to 140sq inches
If you don't have a ton of noise what ton have is leaking..Need a ductulator to check the sizing of duct. There free ones online.
Heat pump in heating 450cfm
Hp thermostats have a emergency heat mode could turn on burner or 2 nd stage heat turns on burner.

 

[Fitter30]

The best heat ever floor radiate either electric or water, radiators then fin tube. Want the heat pump efficiency with fin tube Air to water heat pump system.
Floor radiate quiet, even and when coming in from being chilled to the bone laying on it.