Washington, DC · Member since 2016 · 123 posts · 42 votes
Wanted some ideas/opinions on adding a mini-split to a property in the Mid-Atlantic Region. The main purpose is for cooling (a must, gets unbearably hot in the summer), but hoping to be able to get rid of the radiators as well in a 600-700 sqft space.
I know radiators with a boiler are considered more efficient, but removing them and their piping would enhance the usability of such a small space. It would also limit the number of openings in the walls, allow for better weatherization and sealing. (I would consider radiant floor heat instead since theres a possibility the flooring will be updated as well but I have heard that it costs a lot. If you have comments on this feel free to add though)
I have considered replacing radiators with newer ones that take less space but the minisplit for cooling is a requirement, and I feel like it would be an opportunity to have both.
1 - What are some mini-split basics I should understand before choosing a contractor?
2 - What are your thoughts on the efficacy of mini-split heating in the Mid-Atlantic region? (Maryland, Virginia, PA, Del)
Rental Property Investor · Phoenix, AZ · Member since 2016 · 553 posts · 314 votes
5y
Mini splits are more efficient than any other way to heat and cool. You gas boiler with radiator heat is limited by the thermal efficiency of the boiler. It can't be more than 97% efficient. Meanwhile, a mini split is more like 250% efficient, because it uses one unit of energy to move 2.5x as much heat.
This is effected by temperature. When temperatures are warm (47° is where this is tested) a Mitsubishi unit might have, depending on the unit, an efficiency of nearly 400%, meaning it is 4x as efficient as electric resistant heat. At 17° that will fall to 280% or so. Still very efficient (almost as efficient as gas heat once you include the losses at the power plant. In other words, above 17° you will use less gas to heat even if your power grid runs on gas). At -5° if will still put out the heat that it is supposed to, but efficiency will fall.
You may need supplemental dehumidification and if you have a tight enclosure you might need supplemental ventilation.
Anything you can do to tighten and insulate the building will help ensure that this project is successful.
The proper way to size a mini split is to use a Manual J calculation and to use results from a blower door test as an input for air infiltration. Some of the HVAC guys I talk to tell me that they routinely find heating equipment that is 2x or 3x the size that the space actually needs, because there are so many fudge factors built into the heat load calculations. Furnaces can handle short cycling much better than heat pumps can, so it is important to be accurate.
Washington, DC · Member since 2016 · 123 posts · 42 votes
5y
Thank you so much for your responses. My biggest concern is first the effectiveness of the heat. Will the tenant be satisfied with the heat or constantly feeling cold if I install a heat pump? Would that limit me to only using the heat pump for cooling? The goal being to get rid of the radiators.
so... Can the heat pump pump heat hot enough to heat the home on its own? (figured I'd ad a little alliteration and rhyme in there :-D)