Do I need two heat pumps to heat and cool my house?

Question

We are currently putting a 576 square foot addition on our exiting 125 year old farm house of 900 square feet. My contractor tells me it would be cheaper to install a 1.5 ton heat pump in the addition and a second 2.5 ton pump in the original house rather than try to get one pump to service the whole house (original + addition). This doesn't sound right to me. Does anyone out there have any knowledge or experience that might help me on this? Thanks.

Answer 1

You need a 3 ton unit for single job.

You can put push fans in the ducts for that extra room.

Not being there I can see his point.

Answer 2

HVAC Tech.: your contractor is correct. However, depending on what part of the country you live in and how cold it gets in winter there, you may need additional sources of heat. What if the electricity fails? The heat pumps won't work. While they are safe enough, they are nit the most economical way to heat your home. Have a back-up. Gas or propane are good back-ups as long as the heaters do not require fans or blowers. Beats freezing!!! Good luck!!

Answer 3

It really depends on how difficult the ducting will be.  2.5 tons sounds like it may be enough to handle the addition,  your hvac contractor will (should) know for sure.  A second system will be a bit pricier, but will give you the option of setting temps a few degrees off of one another, which can save you a few bucks on energy. ( Keep the temp where you want it in the area that you occupy, turn the other system back a bit).   You may also want to consider a ductless mini split system in the addition, ...it'd save you a few bucks on the install, and they work really well.  

Because there are so many variables, ask a few hvac contractors to give you some different ideas on how to address the issue, and go with the one you like best....relying on just one opinion doesn't always get you the best setup.

Hope this helps.

20+ yrs HVAC Tech

Answer 4

There is generally an economy of scale associated with initial capital projects - e.g. a 2 ton unit cost less than 2 - 1 ton units - in the upfront.

There is generally a cost of scale in operating costs - e.g. if really only needed 1/2 ton cooling capacity MOST of the time, paying to run a 2-Ton capacity cooler will cost more (less efficient not a prime operating efficiency uses more energy to do the same thing as a 1 ton or 1/2 ton could have) - but how much is enough - do you want to be the most efficient and hot on a hot day, or pay a little more and be cool on a hot day.

Then there is split zone - lets say on (most) x*x days you need up to 2-1/2 tons and most of that load will be in the main home (centralized)/living area. Let’s also say that ducting is in place for this demand. And let’s say that on some days you will need YYY (a little more). And on those days, that need can be limited to the periphery of your home - e.g. bedrooms, utility rooms, etc. Let's also say that the ducting will have to be new for this system.

The contractor is offering you an independent 2 zone system. This would allow you to shut a door and turn a thermostat up during the day to the bedrooms - so you would not have to pay to cool during the day (when you probably are not using), and keep the main home cool. It will also save you the cost of labor and materials to modify and retrofit a duct network if 1 is already installed.

The airflow, distribution, and economics will be dependent upon your usage and specific home lay-out. I suggest that you ask your contractor to lay-out the economics before you commit to it. But there are many homes with 2 zone dependent (mine is zoned with 1 Heat pump) and independent heat pumps.

Answer 5

What is the insulation like in the 125 year old house.  If it has been renovated and has adequate insulation, then you really don't need an extra zone heat pump.  The other thing is how much you'll be in the new addition.  We have one zone in our house which cools up and down adequately.  So I think insulation is a factor to the total job.

Answer 6

You would be spending about $2000.00 more for the equipment for 2 systems than for 1 system, but you may spend twice that to re-size your existing ducting and add for the new side.

Your existing duct work may not need to be modified if you go with the 2 system route, a new duct system would just have to be added for the new part.

If you went with just one system the ducting on the old side would have to be modified, and maybe completely as the ducting would be sized for only 2.5 ton rather than the 4 ton you will need.

2 systems may give you better temperature control and the added benefit of having some comfort if one unit is broke down.

Without knowing all the details my best guess is you will spend $2000.00 more to go with one system because of the ducting and labor required.