These came up in a topic I had posted in the boiler room about tankless water heaters as heat sources for baseboard heat. So I thought maybe a seperate topic might be in order. The basics: We are looking for a) central heat and AC in our Old House and b) potentially installing them in the Cottage as backup backup heat and for central AC The Old House: built in the 1920's 1 3/4 story (part of the ceiling upstairs is the roofline) two bedrooms upstairs somewhat open concept downstairs NO basement (crawl space, not a slab) VERY small utility room that cannot house a standard boiler never had central heat NG available blown in insulation in the walls relatively new (10 yrs?) anderson windows @850 sq ft No attic currently heated with two Lopi gas stoves (Small Heritage Bay, living room and Berkshire in one bedroom) newer (within 15 years) electric service from the pole in, with plenty of space for more breakers (it was sized to double what the house currently needs in case someone ever wanted to add on) we lived here 15 years but have now moved to the Cottage, this will now be a rental. KISS is important given that renters will be living here The Cottage built in the 1950's single story choppy layout originally a summer cottage, at least one wall has no insulation the Republic is definately enough stove to heat it, and we have to run small short fires in shoulder season Ventfree backup heat We do plan to add more insulation in the attic at some point no basement, most of the cottage is on a slab, the living room is an addition with concrete block foundation walls and dirt floor below, but there is insulation between the floor joists mostly original windows with alumium storms, they aren't very leaky two 8' sliding glass doors originally had baseboard heat that we removed-the boiler was old and potentially not working, and the pipes were full of blown out spots from an improper winterization-we counted 20 before we stopped bothering. We live in WNY, so both locations are subject to temps that occasionally drop to single digits. Teens do occur, but most of the time we bottom out in the 20's. The Cottage is between open fields and the lake, so it is subject to some pretty good winds (a normal day is 10-15 MPH). We plan to leave at least the living room stove at the Old House as secondary heat, it is thermostatically controlled. We would need something in both bedrooms and the main floor downstairs, potentially the bathroom and utility room although those two rooms could also use another heat source, such as electric baseboard. the bedroom stove doesn't run long when it is on, MAYBE half an hour when it warms from 50 degrees at night and usually 15 minutes avery few hours after. the living room stove runs pretty much 24/7 once it drops to the 20's, to keep the house in the 70 degree range. Our usage for the Cottage would be in case we want to/need to (parents who live states away getting older) go out of town for more than a day or two in heating season and we don't want to rely 100% on the VF and for AC. We still plan to heat 100% with the lopi when we are there. Are mini/multi splits a feasable solution here? I'm more concerned with the Old House.