[Curmudgeon10]

We're selling out home and looking at replacements. For a variety of reasons, the search is centered on existing homes vs. new construction. Typically, we encounter homes with baseboard heat also air-conditioned. The cold is delivered usually via a pretty ugly ceiling vent in the middle of the ceiling in the smaller rooms (bedrooms and bathrooms, for instance) and perhaps two of those things in the larger living spaces.

Are there any efficiency or other reasons why that existing duct work could not be used with a new high efficiency heat pump, one that delivers both heat and air conditioning, if we decided to tear out the base board heat and upgrade the whole system?

 

[yuri]

You can use a horizontal furnace in the attic and add a heat pump to it or a fan coil unit with electric heat strips with a heat pump also. If the heat pump cannot keep up in very cold weather then the heat strips cut in. Point is you can do whatever you want. Sometimes the ductwork in attics is VERY poorly done and with flex pipe which can be kinked or leaking. You should get it all checked by a reputable contractor.

 

[Curmudgeon10]

You can use a horizontal furnace in the attic and add a heat pump to it or a fan coil unit with electric heat strips with a heat pump also. If the heat pump cannot keep up in very cold weather then the heat strips cut in. Point is you can do whatever you want. Sometimes the ductwork in attics is VERY poorly done and with flex pipe which can be kinked or leaking. You should get it all checked by a reputable contractor.

OK, thanks. It sounds like new ductwork would not need to be run, rather, just insure existing lines are intact and have no leaks.

 

[roughneck]

In older homes duct was often run for heat only systems. And will not have enough flow for cooling.
During air conditioning fitouts in the 1980s and 1990s it was common for contractors to put in duct systems with a single return and supplies referred to as spider or octopus systems. These are almost entirely made of flex and flow very poorly, especially with newer ECM motors.

 

[Frank Lavorngia]

I'll tell you one of the most deciding factor on your existing duct is, Is the duct insulated or not" You don't want it to sweat.

 

[Heating Solutions]

Bottom line is no equipment should be installed or replaced if the existing duct system can’t support the equipments required airflow… best way to do hvac is a room by room load calculation and then size the equipment and duct system appropriately. If retro fitting something and the duct system won’t be changed then in my opinion it’s always best to size the equipment based on the duct capacity and supplement if needed on the worst case scenario days.

 

[SW Dweller]

Hire a contractor that will do the calculations for size, tons or Manual J. Tell him you want him to do a Manual D which is for the duct work. You can find on line resources to help you with both. Old duct work may not be big enough for a new heat pump. You do not know until you do the Manual J the tons will dictate the cfm of the new unit. Once you know the cfm then you can do some calculating again on line resources and discover if the duct work is large enough. If it is then make sure the duct is inspected and or cleaned before using the new unit. Last statement is based on not knowing the age of the home or ductwork.

The Manual J will also allow you to play around, what if I add another R19 blanket of insulation after every one is done working.

Heat Pumps do not like really cold weather. Get the low operating temp from the contractor and model number compare this number to the local design low temp. Usually published by the AHJ, county or city. I have had heat pumps for heat and prefer gas. Heat pumps run longer and unless you put in backup heat which is $$$$ to run. Other wise IMO the air comes out luke warm it will heat your house and efficiently.

I put in mini splits in my new home. Design temp for my area is 20F low temp on the units is 05F. So I should be OK for my desert location.

I do not like attic units. They cost more to fix if something goes a wander some day.

The way you heat is connected now will probably mean you will get an UPFLOW unit in a closet somewhere.

Good luck with your home search.

 

[user_12345a]

Heat Pumps do not like really cold weather. Get the low operating temp from the contractor and model number compare this number to the local design low temp. Usually published by the AHJ, county or city. I have had heat pumps for heat and prefer gas. Heat pumps run longer and unless you put in backup heat which is $$$$ to run. Other wise IMO the air comes out luke warm it will heat your house and efficiently.

There is no such thing as a heatpump low operating temp rating.
Capacity and efficiency gradually drop as it gets colder outside - unless it is a cold climate model which is specifically engineered to maintain full capacity as it gets colder outside.
Efficiency still drops on those.

Running long is a good thing for comfort and efficiency; cycling on and off is an artifact of having too much capacity; most furnaces are oversized for the worst case heating load and shut down before even hitting manufacturer rated heat output and efficiency.

Supplemental heat done right will only come on to supplement as required, will not reduce cycle length unless it comes on when it shouldn't.

 

[AllanJ]

With all of the supply vents in or near the ceiling you will want to use ceiling fans to distribute heated air in winter.

More elaborate duct systems had both ceiling level and floor level vents for single arrays of ducts between stories, with louvers or dampers in the vents manually adjusted for the season.

 

[user_12345a]

With all of the supply vents in or near the ceiling you will want to use ceiling fans to distribute heated air in winter.

More elaborate duct systems had both ceiling level and floor level vents for single arrays of ducts between stories, with louvers or dampers in the vents manually adjusted for the season.

If floor level return is added, the fans aren't necessary.

Oddly enough this is far less of a problem with heatpumps because the supply air is cooler than from a furnace and mixes better - instead of rising up and staying at the ceiling.