Ducted split tired into existing furnace?

[yugami]

I live out in the country so we have propane heat. I've been thinking about the possibility of a central/ducted split system.

Where I'm at in Michigan the winter lows can be very unpredictable from year to year. Sometimes a week of -12f, sometimes it never gets below 25f.

So it would be nice to size the split to handle the needs to a certain point and retain the furnace for the remainder.

It's this doable? I've done a little basic research but most of the info I'm finding is sales oriented. Probably need to find an HVAC company and take with them, but if like to work through a little of this before dragging them into what's currently a maybe project.

 

[jack stand]

I think a large part of these m/s systems efficiency is that they don't suffer the losses of ductwork, especially less than perfect ductwork. They also seem to just purr along very slowly almost constantly maintaining the set temperature vs a huge blast at full power and compressor speed periodically giving the wide temperature swings.
I only speak from my experience and am not "in the bizz"
Someone will be along that knows better and I think they've come a long way with traditional ducted type HP systems but it won't have the "split" terminology... I think

 

[Yankeefarmer]

I think a large part of these m/s systems efficiency is that they don't suffer the losses of ductwork, especially less than perfect ductwork. They also seem to just purr along very slowly almost constantly maintaining the set temperature vs a huge blast at full power and compressor speed periodically giving the wide temperature swings.
I only speak from my experience and am not "in the bizz"
Someone will be along that knows better and I think they've come a long way with traditional ducted type HP systems but it won't have the "split" terminology... I think

What Is a Split System? | Carrier Residential

A split system has indoor and outdoor components to keep your home warm in winter and cool in summer. Learn more.

www.carrier.com

 

[jack stand]

Well I'll be, sounds like the same systems that were installed in the 500 homes a year that I was involved in for the past 30. Although not as anything to do with the hvac system, I did have friends with what they called a heat pump system that switched to "emergency" or "auxiliary" heat at about low to mid 30's. It was just electric resistance heat that was very expensive, and this was in the mid Atlantic area and big national home builders. No one was happy with them. The ac side was fine but the last thing they "pumped" was any real heat.
I've been away from that rat race for almost 15 years and I'm sure there's been improvement since. My first and only experience with a heat pump is my mini split that we put in for the ac. Turns out that they make hot air and do a fine job heating our place completely until we fire up the wood boiler and radiant heat sometime in December.
If the OP has similar results with his proposed split system, he'll be a happy camper. I don't think that our m/s dings the electric bill for more than $10/month in our situation.

 

[Yankeefarmer]

As jack stand writes, these systems have come a long way. Using inverter technology, heat pump systems can provide useful heat at outdoor temperatures below zero F. @yugami, it sounds like you are interested in what is referred to as a ”dual fuel” system, which I think is a misnomer because one of the “fuels” is electricity to power the heat pump. These came about, I think, because the early heat pump systems did not produce much useable heat below about 30 deg F, but could be more economic than other fuels when heat is needed in the 40 to 60 degree range.

From what little personal knowledge I have, HVAC contractors are reluctant to embrace heat pumps as the sole heat source in cold climates, thus the duel fuel approach is viable, but may not include a cold-capable heat pump. When I built my new shop, I asked my HVAC guy to quote a dual fuel system, and he quoted a 3 ton heat pump/100k btu/hr propane furnace system. His price was too high for me at about $14k, so I did some research and bought and installed myself a 5 ton (60,000 btu/hr) cold-capable ducted split system for under $5k. This past winter we only got down to about -1 deg F, and my system provided all the heat I was looking for.

Although a heat pump system can keep your space at the comfortable temperature you want, the air it is providing will likely only be in the 80 to 90 degree range, not the +100 degree temps a propane or oil fired system will deliver. So your room temperature will be comfortable, but to your body it may not feel nearly as satisfying as having baseboard heat or sitting by a wood stove.

One other thing to be aware of with heat pump systems is that they are not all created equal. My system can be programmed to operate as either a 4 ton or 5 ton system. But regardless of how it is set, once the outside temp is down to about 20 deg F, the heat output is virtually the same, somewhere around 3-1/2 tons. A popular competitor’s 5 ton system will produce even less heat. So when considering systems, be sure to ask for the output and efficiency curves vs. outside temperature for any systems you are considering.

Edited to add: You may or may not be able to add a split system coil to your existing furnace. It depends on coil sizing and other factors. But evenif you have to replace the furnace, that will be only a small part of the total price tag.

 

[jeepxj]

As jack stand writes, these systems have come a long way. Using inverter technology, heat pump systems can provide useful heat at outdoor temperatures below zero F. @yugami, it sounds like you are interested in what is referred to as a ”dual fuel” system, which I think is a misnomer because one of the “fuels” is electricity to power the heat pump. These came about, I think, because the early heat pump systems did not produce much useable heat below about 30 deg F, but could be more economic than other fuels when heat is needed in the 40 to 60 degree range.

From what little personal knowledge I have, HVAC contractors are reluctant to embrace heat pumps as the sole heat source in cold climates, thus the duel fuel approach is viable, but may not include a cold-capable heat pump. When I built my new shop, I asked my HVAC guy to quote a dual fuel system, and he quoted a 3 ton heat pump/100k btu/hr propane furnace system. His price was too high for me at about $14k, so I did some research and bought and installed myself a 5 ton (60,000 btu/hr) cold-capable ducted split system for under $5k. This past winter we only got down to about -1 deg F, and my system provided all the heat I was looking for.

Although a heat pump system can keep your space at the comfortable temperature you want, the air it is providing will likely only be in the 80 to 90 degree range, not the +100 degree temps a propane or oil fired system will deliver. So your room temperature will be comfortable, but to your body it may not feel nearly as satisfying as having baseboard heat or sitting by a wood stove.

One other thing to be aware of with heat pump systems is that they are not all created equal. My system can be programmed to operate as either a 4 ton or 5 ton system. But regardless of how it is set, once the outside temp is down to about 20 deg F, the heat output is virtually the same, somewhere around 3-1/2 tons. A popular competitor’s 5 ton system will produce even less heat. So when considering systems, be sure to ask for the output and efficiency curves vs. outside temperature for any systems you are considering.

Edited to add: You may or may not be able to add a split system coil to your existing furnace. It depends on coil sizing and other factors. But evenif you have to replace the furnace, that will be only a small part of the total price tag.

Conventional heat pumps only produce 100% heating capacity above 47 degrees Fahrenheit. In comparison, the patented Mitsubishi Electric Hyper-Heating heat pumps have the ability to produce up to 100% heating capacity at 5 degrees Fahrenheit and guaranteed heating capacity down to -13 degrees Fahrenheit.

i'm not sure i'd be totally comfy in CT doing heat pump only. maybe if i knew i could flip over to electric resistive for that one night a year.

 

[Yankeefarmer]

If it were my house, I’d want an alternate source of heat than just the heat pump, preferably one like the wood stove we use which will keep us warm even without electricity. My heat pump install was in my shop, where I figured the worse that could happen if it didn’t perform at the coldest temperatures was that I wouldn’t be able to achieve my target inside temp. I was pleasantly surprised at how capable my heat pump is, even on humid cold winter days when it has to periodically go into defrost mode.

 

[yugami]

Sounds like I created a weird constraint. I was only thinking of leaving my perfectly functional furnace in place "just in case" But doing a little more looking around I see some pretty good systems for what would be a very quick return based on where my propane prices went to recently.

The variable speed systems seem like a great idea.

What system did you guys go with just as an information point? I see a decent looking goodman in the size I would need.

 

[Yankeefarmer]

I do not have a dual fuel system. Mine is a Mr Cool Universal, 5 ton, because I calculated a heating load of 60k BTU/hr. There’s another thread here where I posted a link comparing the manufacturers’ published heat output for a Goodman 2 stage 5 ton heat pump and the Mr Cool Universal 4-5 ton. This is the comparison(keep in mind there may be other Goodman units with better low temperature performance):