Single Head vs. Multi-Head Ductless Displacement Design

Ductless as a technology is nearly unbeatable. Not only is customer satisfaction at an all time high since it became a mainstream offering, but customers are getting more system efficiency on the dollar (value) than ever before.

In this post, I am going to focus on system design. Specifically, the single head and multi-head displacement concepts. So the question is...

What are the MOST popular ductless systems designs?



To answer this question, we have to look at 2 types of installs; Single Head Displacement and Multi-Head Displacement (we are not discussing Full Coverage in this article)

Single Head Displacement (SHD) - Most Popular:

The SHD design concept was and is born of PAIN, as in, the cost of heating. When we talk about displacement; another word that could be used is supplement. We are keeping the "old system" for cold weather backup and displacing it with the ductless for as many heating hours as possible.

Now, that doesn't mean that each and every customer even uses the "old system", in fact, many do not (again, to avoid pain), but it needs to be there in case of the crazy weather that comes about every 15 years or so. The fact is that while ductless systems are not nearly as susceptible to cold weather as traditional heat pumps, they still lose about 15% of their optimum capacity in the worst weather. We have to take this into account. There are times, if the home is small enough and stores heat well, that we can size a single head ductless to heat a home in worst weather, even with the 15% capacity loss, but it is rare.

To make this simple, I have listed below a sampling of some scenarios where we would use SHD:

• Before: Rambler with electric baseboard or wall heaters. After: Single Head in Main Living Area to displace core and leave electric heaters in bedrooms.
• Before: Rambler with electric/gas ducted heating system. After: Single Head in Main Living Area to displace core and leave heating system in place, however, mostly used for back-up or morning recovery.
• Before: 2 Floor with electric/gas ducted heating system. After: Single Head on Main Floor for full coverage of core as well as shut down air flow from ducted system. Move thermostat and return to second floor or basement for "zoned control" of home through the ducted system. (it is common that if there is a hard to reach bathroom or utility room on the main floor, we may leave this register open so some supplemental heat is provided)

Multi-Head Displacement (MHD) - Second Most Popular:

While MHD and SHD have very similar design concepts, MHD adds a second or third head (4 is rare) to the displacement equation and is generally more of a comfort consideration. For instance, the person who is thinking about single head, but has a Master Bedroom on the far side or upstairs that gets too cold or hot on its own and wants control in that room, will add a second head. Now, take that same scenario and add a basement family room or rec area, now you are up to 3 heads. The is many reasons to go to the MHD design concept, but mainly it goes along with having a bigger home that requires displacement in more common areas of the home.

If you are considering ductless and want some advice on your design considerations, please email me.

Thank you for reading!