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Thinking about a mini-split

10 years ago

I live in a 1910 2-unit building (upstairs/downstairs; I'm in the downstairs unit) in the San Francisco Bay Area. The only heating or cooling equipment in either unit are centrally located gas fireplaces, which are supplemented with electric room heaters, electric mattress pads, and electric blankets. The house has attic insulation, floor insulation for the lower unit, but no insulation between the lower and upper unit. No wall insulation.

My house is below 60 degrees for large stretches during the winter. It's never gotten below 54 degrees even when I'm not heating at all (most of the time), thanks to solar heat gain (large expanse of southwest facing wall with lots of windows) and a mild climate. While the solar heat gain keeps me from freezing in the winter, it's a problem in the summer. This past summer was particularly bad, as the Bay Area had unusually high humidity and temps dropping at night the way they usually do.

I'm thinking of getting a ductless mini-split to heat/cool my living room, which is where we spend most of our time. It's also where we engage in more sedentary activities (TV watching, computer use) which is when the cold winter temps really become a noticeable problem. The living room is only 12x15, has a northwest facing bay window on one of the 12 ft walls. The other 3 walls are interior walls, 2 or which have wide openings (5-6 ft) into the adjacent rooms. As previously noted, there is no ceiling insulation.

Now that I've overwhelmed you with background detail, my questions are:

1) Is this an appropriate situation for a mini-split?

2) What size (approximately) would I need?

3) What manufacturers are recommended?

4) How do I find an experienced contractor?/Does anyone have any recommendations in the SF Bay Area?

5) How bad will the heating and the cooling performance be, given the envelope situation I described?

6) When would be the cheapest time of year to do this (i.e. when are HVAC contractors the least busy)?

Comments (19)

  • 10 years ago

    1. Definatly 2. 18 to 24k 3. Compare local price, seer and warranty. 4. Call mfgrs for dealers and no. 5. Better than other options. 6. On the West coast that would be now until next April.

  • 10 years ago

    Gas heat is less expensive with efficient heaters, but probably not with unsealed gas fireplaces. If you don't need that much heat, it may not merit installation of separate heating appliances if you are going to install a heat pump for cooling. If is would pay, some direct vent wall heaters might be worthwhile.

    Mini splits are best for open floor plans. If you install many units in a places with lots of small rooms, equipment costs go up quickly. A ducted system might be added to your home with partial dropped ceilings used to hide ducts. This might be unobtrusive or terrible-looking depending on your situation and the skill of the designer. Maintenance is higher with multiple mini splits compared to a central system. If you have a structure with good exterior insulation, the interior temp can be more effectively controlled with spot heating because heat moves through interior partitions faster than exiting the building. Unfortunately that is not your situation.

    Is this a good spot for a mini split? I have 7 indoor units in a hot, humid climate and I like their operation. Ask yourself if a window unit or a wall heater would serve you well, but with quieter operation than a window unit. If so, go for it. The mini splits are great at humidity control which is a real plus for me. Mitsubishi, Sanyo, Toshiba and Daikin are all recommended by most people. Pay attention to features like a dry cycle to dry the unit out after cooling use to prevent fungus growth. (Dry cycle is different from a dehumidify setting which biases operation towards humidity removal rather than cooling. Note also that the dehumidify setting WILL cool even though some people will try to tell you that it does not.) Make sure there is a true set-back rather than just on-off timer if that is important to you. If you want remote control from off premises, look into that. You will likely see variations in what they will do in some of these kinds of controls.

  • 10 years ago

    Thanks for the responses!

    To clarify, I have a zero clearance gas fireplace, not gas logs in a traditional fireplace. No chimney, just stovepipe, so not a major source of heat loss. It's in the dining room, not the living room, and the heat just isn't making it to where I need it.

    Also, I'm only looking to heat/cool one room, not the whole house, so I wouldn't be looking at multiple units.

  • 10 years ago

    What is electric rate? I would ask about zoning the mini split.

    IMO

  • 10 years ago
    last modified: 10 years ago

    For heating, I think a better choice would be a through-the-wall direct
    vented gas unit. They're inexpensive, put out a lot of heat and operate economically. If
    A/C is also desired, I'd get a second unit, a mini-split or even a PTAC
    and use it for just cooling.

    If this person uses the area's large provider (PG+E), usage in an apartment/condo (compared to a house) would probably be mostly be at the lowest tier that starts around 17 cents/ kwh. Before considering the use of a mini-split. For comparison, the tiers are stair stepped upward with usage and my bill regularly gets into the top tier of 30 cents/kwh. That's at a usage level of about 700 kwh per month.

    There are a few small towns around that have municipal electricity agencies that have lower rates.

  • 10 years ago
    last modified: 10 years ago

    Hopefully you can get some recommendations local to where you are. If you are looking at Mitsubishi there is a contractor list on their website (mitsubishicomfort.com, "find a contractor") and then you could check yelp reviews? I expect the other mfrs have something similar.

    We used Residential in Campbell -- don't know whether that is too far from you.

    Good luck!

    [edited: PG&E offers different baselines for folks who have electric heating; if you are going to be using a mini split as your main heat source you might ask whether there would be some savings in switching to the electric heat plan if you are currently on a gas heat plan (sorry this might not be the right terminology). I did not know this for several months but luckily they were willing to change our bill retroactively and credit us the difference.]

  • 10 years ago

    I have PG&E, and am actually on their time-of-use rate. For October, I was paying 14 cents/kWh off peak (47 kWh use), 21 cents for partial peak (16 kWh use), and 33 cents on peak (12 kWh use). I also got a bill credit for low summer use that more than offset my September bill (gas and electric--I ended the month with a $3 credit). Way complicated. I wouldn't necessarily stay on the TOU plan if I got AC. But yes, generally a high rate area.

    A "through-the-wall direct vented gas unit" sounds like it would need to be installed on an outside wall, which presents two problems here. The room only has one exterior wall, and it faces the street, so aesthetics would be a negative. Second, that street-facing wall is almost all windows (and I have a sofa against it that takes up most of the wall).

    Are there any ceiling-mounted gas radiant heating units that don't look terrible? My grocery store has these at the checkout stands. I love standing under them but they are ugly as sin. But the idea of heating the people rather than the space has some appeal.

    Oaktown, I'm in Oakland not far from Lake Merritt (near Highland Hospital).


  • 10 years ago

    If I understand correctly, the SF climate is very mild so you don't need much heating or cooling at all. In most energy markets, this would make it not very rewarding to invest in expensive, energy efficient equipment. This is partially or wholly offset by high electricity (and maybe gas?) price.

    At the first mention of wall heaters, my first thought was your problem, that you might not have much wall space. Then we are back to investing in two efficient heating and cooling devices when the mini split could do both.

    I am not familiar with your fireplaces so I don't know how efficient they are. If they take room air for combustion, rather than outdoor air, it is like having a exhaust fan evacuating your home while it is running. This will cool off any areas of your house where air can leak in that are not near the fireplace. A direct-vent heater will use outside air. I don't know if they are condensing and if so, you could not use one if you could not deal with the condensate. Think about it, however, what are your total gas heating costs for 10 years? If it is $5000, increasing efficiency by 15% will net you $750. Is that worth investing $3000 (completely fabricated cost) in a heating-only appliance? Maybe, if there is a difference in comfort.

    Basically, from a cost standpoint, you need to take the cost of the appliances plus the projected cost of fuel to calculate the lifetime cost of heating with the mini split, your fireplaces or direct vent heaters if you can use them. See what the difference is and then you will know if it is significant. Then you have to somehow factor in the comfort of having cooling and dehumidification with the mini split. Then there is the comfort difference between the heating methods.

    Are there any energy efficiency programs in your area that would pay for a energy rater to come in, make measurements and make recommendations? They might run these numbers for you. Even if you have to pay for it yourself, it might be worth it.

  • 10 years ago

    The climate here is very mild. It rarely gets below freezing, and then its only at night and usually no lower than the high 20s. We'll get summer temps into the 90s at times, but it usually cools off at night (not this year, though, for long stretches).

    The fireplace is direct vent. I think it's only about 70% efficient (much less than a furnace). The problem with it is distribution--given the lack of ceiling insulation, it just can't even heat the room it's in, much less the room I need heated. If I put in ceiling insulation and installed a fan to redistribute the heat, I would still have an overheated dining room and underheated living room.

    This is never going to make sense if you look at it only in terms of monetary costs and benefits. I essentially don't heat or cool my house at all (just electric blankets and mattress pads). I pay $25-30 a month for electric and gas, year round. Whatever I install, I will be using more (possibly a lot more) energy than I am now. On the other hand, I may be able to bring my interior temperature (in one room, anyway) up into the 60s in winter and down into the 70s in summer.

    PG&E has an advanced home upgrade program (their basic home upgrade program doesn't apply to duplexes). But the incentives are based on savings, and I think our baseline is so low (even taking into account my upstairs neighbor's higher energy bills) that I don't think the incentive would amount to much.

    If I was really interested in saving energy (more than improved comfort), I'd get a 40 gallon condensing gas water heater to replace my 60 gal std unit. Or a tankless water heater. Or a condensing tankless water heater. Water heating is the lions share of my energy bill.

  • 10 years ago

    Do you think some extra air sealing might help?

    To me, being comfortable would be worth the cost of a mini-split.

    Good luck! (and love your avatar, my kitty looked like that)

  • 10 years ago

    How tall are the rooms? In my house, the high wall mini splits make good ceiling heaters. That is exacerbated by the fact that I have very cold floors in the winter. I have 9 ft. ceilings. The air stratifies when the mini splits approach the set point because the blowers slow down and the floors are cold. Rooms with ceiling fans are much more comfortable due to this. You might be able to tackle this problem by manually bumping up the blower speed, but that will increase the noise.

  • 10 years ago
    last modified: 10 years ago

    I think you need to find an HVAC contractor to come out and give you some choices. Whether it's running ducts in the crawl space (I presume there is one) or interior spaces, or converting the fireplace to a heater, there most certainly are options. I would bet if you took a survey of your Lake Merritt area neighbors, you'd find most have well functioning gas heat systems and few have electric ones, mini-splits, or air conditioning.

    Even in a modern residential building (much less one from 1910), you wouldn't find ceiling insulation for the first floor of a two level residential structure except when used for sound muting. Insulation is predominantly for structural separations where the temperature on one side is significantly different from the other. In a residence, even if it's two separately owned units, it would be expected that the upstairs temperatures wouldn't differ significantly from downstairs and thus insulation wouldn't be thought to be needed.

  • 10 years ago

    Okay, you've convinced me that while the mini-split might do an adequate job of cooling, it isn't going to cut it for heating (ionized, I have 9-foot ceilings and your comment about mini-splits making a good ceiling heater is probably spot on). Snidely, pretty much no one here has AC. I've always just come home and thrown the windows open. To my frustration, the weather patterns this year were just weird and didn't involve temperatures dropping at night (hence my current motivation). I also think that more of my neighbors have inadequate heating systems than you give them credit for, although gas is probably the norm. I think central ducted systems are uncommon in my neighborhood (most houses are from the 1870s to the 1930s, there are lots of rentals, and it's not a high income neighborhood).

    I will continue to mull it over. Thanks for all the input.

  • 10 years ago

    Mini split heating might be alright for you. I have a raised home with an open crawlspace. Glass batt insulation was removed in extensive flooring/subfloor repairs and I hope to get it re-insulated. I have decent attic and wall insulation. In the winter under the floors must approach the outside temps which can freeze sometimes. Your floors might be warmer than mine. That has to be true if you don't have an open crawlspace. I think that you might want to find a situation more similar to yours before you make a decision. At any rate, if you are thinking of adding a mini split AND some kind of gas heater nearer the floor, you could try a mini split and add something else later if you need to.

  • 10 years ago

    cawaps can see what an HVAC contractor or two recommend. It was indeed a warmer than normal summer. I myself am having A/C installed with a conventional configuration for our house. We've lived here for a few decades without it.


    OP is very unlikely to find anyone with significant mini-split experience in her area. It's also an expensive overkill solution to her needs, in my opinion.

  • 10 years ago

    The floor units are much better after having a wall mount and floor mount. Floor mounts keep the floor area warmer and keeps from short cycling as much. Fugitsu makes a nice floor mount and has a broad range. 3100 btus minimum on the rffl models and maxes at 21000 btus on heating.

  • 10 years ago

    Yes, but toadman77, you are in a heating-intensive area. For cooling and dehumidification, closer to the ceiling is best.

  • 5 years ago

    RIGHT SIZE MINI SPLIT.

    https://www.minisplitairconditioningsystem.org/


    9000 Btu|3/4 Ton|(under 400 Sq Feet)

    12000 Btu|1 Ton|(400-600 Sq Feet)

    18000 Btu|1.5 Ton|(600-800 Sq Feet)

    24000 Btu|2 Ton|(800-1200 Sq Feet)

    30000 Btu|2.5 Ton|(1200-1500 Sq Feet)

    36000 Btu|3 Ton|(1500-1800 Sq Feet)

    48000 Btu|4 Ton|(1800-2000 Sq Feet)

    60000 BTU|5 TON|(OVER 2000 SQ FEET)

    BENEFITS OF A DUCTLESS MINI-SPLIT.

    https://www.airconditionersductless.com/


    EASE OF INSTALLATION

    In most cases, you can connect the air handler with the compressor/condenser by running the electrical conduit through a three-inch hole in the wall.


    The outdoor unit can connect to the air handler from as far as 50 feet away, allowing you to place it in a less conspicuous area even when connecting to rooms that face the street.


    Also, mini-splits are ideal as a retrofit add-on for old homes without preexisting ductwork. They are increasingly being found in homes that:


    Have a costly heating system but no cooling option

    Have an outbuilding that ducts cannot reach

    Are located in areas with high fuel costs


    ZONING CAPABILITIES

    Chances are you need more than one room heated and cooled, and fortunately, one outdoor unit can power as many as four air handlers. You get the option of zoning, then, without the need for cumbersome ductwork, dampers, and so on. Each room, or zone, can have its own thermostat, letting you condition the air only when those rooms are occupied. There are smart thermostats available that are compatible with mini-splits.


    LOWER ENERGY BILLS

    Energy loss through ductwork accounts for more than 30% of all HVAC energy consumption, according to the Department of Energy. Mini-splits bypass this concern altogether. They also transfer heat rather than generating it through electric resistance or the burning of fuel, so they are very energy-efficient. This will translate into lower bills.