As long as there is some resistance electric heating elements as a backup in all the interior fan coil units you should be fine.

This would also be an advisable option in case the roof top unit failed for any reason during heating season.

SR

One thing that argues against heat pumps now, as opposed to a couple of years ago, is the price of natural gas. Since they are fracking the heck out of Pennsylvania, it has become really inexpensive to heat with gas compared to heat pumps. One often overlooked fact is that heat pumps cost a lot more to buy than gas furnaces so wear and tear adds up. Are you sure you don't want to keep the hydronic heat?

In my home, I've found that the high wall units make good ceiling heaters when the room is warm and the blower slows down. I have a poorly-insulated, leaky, raised house in a hot-humid climate (Gulf of Mexico coast).

Ionized does have a point, the cost of electricity in NYC is high and the cost of gas is low for now but then again you canâÂÂt air-condition with a gas boiler and hydronic delivery.

You might want to keep the hydronic system for backup.

Have you explored an air-to-water heat pump that might allow you to keep your rads and still air-condition with water fan coils?

SR

Here is a link that might be useful: Daikin Altherma

@ionized & @fsq4cw, thanks for the input.

The (low) cost of natural gas is definitely a factor and a strike against using the heat pump year round. Unfortunately, the current boiler is old, inefficient, and would need to be replaced. I think we could salvage some of the hydronic plumbing and radiators, but since we're moving walls and rooms in the renovation, it would wouldn't be free.

@fsq4cw - I will take a look at the Daikin Altherma. However, I think if we decided to stick with hydronic we would bite the bullet and install an efficient boiler for winter use and use the City Multi for summer AC. Over 10 or so years (and assuming natural gas continues to remain cheap), I think the boiler would probably pay for itself ... although I haven't done that math.

Of course, there's a case to made for a simpler system - one less machine in the house to service.

All that said, it's good to hear a City Multi only system is an option and that we won't be living in a cold house in January if we decide to go that route.

Careful, not all of the mini splits have electrical resistance backup heating and that is a very expensive way to heat. When I installed mini splits, I think that only one brand that I looked into had it and it was not Mitsubishi. Things change and I don't have Citi-Multi. I am no expert, but my take on the best low-temp Mitsubishi systems is that they will take care of NYC temperatures in heating season.

As far as keeping it simple goes, heat pumps are a little more complex than straight air conditioners. Ask anyone that has had a reversal valve go bad. I did and, fortunately, it was under warranty.

One really nice thing about SOME of the Citi Multi systems is that they can heat and cool at the same time. If you are doing that at a low level in adjacent rooms, you can get some dehumidification.

One question I would be asking the engineers if , and how much smaller the heat pump/cooling system can be if you only need it for cooling. In my area, you size for cooling and end up with plenty of heating. In NYC, I don't know if it is balanced or you need to have more equipment for heating than for cooling. If you can install smaller parts all the way around for cooling only, you might be able to pay for the hydronic renovations.

Are you planning on using ducted air handlers, individual room units only, or some combination? If you are using air handlers, Mitsubishi might have some equipment that can incorporate a hot water coil that will work with your hydronic heat in areas where you are removing the radiators.

I hope that your engineers are creative thinkers.

@ionized, we're planning on using a ducted system - no visible air handlers like you'd see in a typical mini split install.

We've read about the Citi Multi systems that can heat and cool at the same time - I believe this is for the larger semi-commercial units. I imagine the heat/cool at the same time comes up when you have a server room full of hot computers that need AC during the winter... but it's hard for me to imagine when we would be running heat in one part of the house and AC in another.

We will bring all of the above up with our engineers - thanks a bunch for the advice.

I would not want to pay the electric bill to heat a 4500 sq. foot townhouse in NYC. I assume this house has 10 foot high ceiling and very large windows.

What are the current electric and gas rates? I would think it would cost 2 - 3 times as much to heat with heat pumps than natural gas. Do the math before you make a final decision.

Yes, there's no question that electricity rates are higher than gas - we are waiting on some numbers from our engineer to really see the difference in annual costs. However, with a natural gas fired boiler and hydronic heating, we're basically heating the whole house all the time, where the City Multi VRF allows us to heat the zones we are actually living in. HOWEVER, I've been told it takes a much longer time to get a room to temperature via heat pump, so it's possible the heat pump would be cranking all the time anyway...

Lot's to think about - thanks for all the advice.

"However, with a natural gas fired boiler and hydronic heating, we're basically heating the whole house all the time...."

This does not have to be the case, however, if that is what your old system did, you might need a lot more pipes to split the hydronic system into zones and that will increase the cost of resurrecting it. It is worth looking into the cost and benefits.

Zoning has more benefit in a situation where exterior sealing and insulation is poor and the floor plan is open compared to poorly-sealed, poorly-insulated homes with lots of interior doors. There is the lifestyle factor too. If most of your rooms are in use at the same time, there is little point to zoning.

Codee, I'm curious where you ended up.

Personally, I have a ~2,500 square foot home (a carriage house in brooklyn) that after a full gut renovation is now both heated and cooled with a CitiMulti setup. A few thoughts:

-- It definitely is capable of heating the house through a NYC winter. We have a neighbors on either side but a 50' long south wall shaded all winter by an apartment building and a 50' long north wall with tons of window. We also have 6 skylights, one of which is huge. And this past January was absurdly cold. And yet we were generally warm. (In part to a very tight house -- no drafts ofany kind anywhere. Any tons of new spray insulation.)

-- It is EXPENSIVE to heat with electric in NYC right now, especially this past month when electric rate skyrocketed. Then again, so did gas rates. Regardless, my electric bill (after you subtract out what I think the baseline non-heating usage is) is typically $200 to $400 a month to heat the house. This past January is was ~1,000.

-- Because the vents are high and a have a fairly open layout I feel like all the heat is up at the ceiling. Ceiling fans would help but they would only really make sense in the bedrooms and honestly, we need lighting fixtures up there, not fans.

-- I wish I spent the money and got radiant heat. It would have been far, far more comfortable and cost a lot less to operate (in part because of its design and in part because it runs on gas). The initial installation cost put me off but when you factor in all the expenses that could have been skipped if we went with radiant heat the up-front cost wouldn't have been so bad.

Do let me know what you chose.

It is considered bad forum etiquette to piggyback onto or hyjack an old inactive thread that OP is unlikely to see or even respond to.

Start your own thread if you expect a reply.

TD

Hi @petestein1

OP here - thanks for the info, it's super helpful. This is indeed an old thread, but it sounds like it would be useful to update it with where we're at in case others stumble here.

As of right now (and we haven't started construction, so this isn't final), we have spec'd out a home heated and cooled only by 3 Mitsubishi PUMY-P60 outdoor units each paired with a variety of ducted indoor units. According to the manufacturer, the PUMY-P60 still performs at ~ 60% of its capacity at 5 degrees F.

However, the past few months have definitely given us pause, as we haven't had a winter this cold in over a decade. So it's really good to hear that your system held up. It sounds like you're saying that while the house was comfortable, the system was working harder than it had to as all the heat was stuck up by the ceiling. We will have a fairly open layout on the first floor, so this is a concern of ours as well. Ceiling fans are out and our ducts will be high up, too.

I've heard (and maybe someone else can chime in here), that hydronic radiant heat can be problematic over wood floors. We'll be relatively small plank reclaimed wood (I'm not sure on the type, as of yet). And, obviously, there's additional expense there that we would rather avoid... i'm not sure it would pay for itself in any reasonable time frame.

I have 9' ceilings. In the default programming mode, the high wall mini splits are good ceiling heaters. The trouble is that the blower speed slows down as the set point is approached so there is less air mixing. Manually setting the blower to the highest speed helps some, but not as much as ceiling paddle fans. It is not a big deal for me because I have some paddle fans and my need for heat is low because of climate.

The most effective way to heat with forced air is to put the supplies near or in the floor. Fault that, return near the floor. Anything else is going to perform relatively poorly. You can't beat basic physics. Radiant in the floor is going to be most comfortable. As far as lifetime costs go, you just have to run the numbers for lifetime cost and pray that your fuel assumptions hold up.

% capacity at a temperature is not the whole story. What is the performance of the system at that temperature? The two measures are certainly related, but what you want to see are COPs at different temperatures.

OP, you are going to have ducts, Why can't you install hydro coils connected to a boiler?

Here is a thought that, although interesting to consider, will probably be totally unproductive. The City Multi systems are so versatile that the engineers should be able to come up with a way to transfer heat from a boiler to your indoor units rather then from outdoors if the temp is too low for a favorable COP. This is probably not going to be cost effective compared to a dedicated heating system.

I see a potential problem with the Mitsubishi City Multi, as eluded to by Pete Stein in mentioning his operating costs this winter. As âÂÂniceâ as the figures look in the Mitsubishi documentation, after you have followed all the asterisks, foot notes and drill down through the original source material at âÂÂAHRIâ for testing methodology, it appears that these units are specâÂÂd out at full load, maximum compressor speed and design conditions that âÂÂcut offâ for that nice COP is at 17FDB/15FWB (Fahrenheit, Wet or Dry Bulb) âÂÂAir Entering Outdoor Unit TemperatureâÂÂ.

So the question becomes what happens below these temperatures, that much of the continent has seen this winter. The answer is probably that your left in the lurch having to make up the difference with electric resistance heating at the worst of all times, after COP drops off precipitously, with a very expensive form of energy, electricity at COP-1.

When designing a system, it may be wise to consider a hybrid system of some sort so that the cost of energy can be ameliorated by using an alternate source of energy, such as gas, when the temperatures become extremely cold, as we know they will - even if you are a âÂÂGlobal Warmingâ true believer.

I would favor a hybrid system using modern hydronics for radiant heating and hydronic cooling with a ground source heat pump backed up by a gas boiler. Over time the greatest costs may be for energy and not the cost of the system, as mentioned in PeteâÂÂs post âÂÂThis past January is was ~1,000âÂÂ. That was for just one month and not at all unusual in my experience!

Hybrid systems with diversified energy sources give us the opportunity to switch fuels as conditions and rates change and dramatically reduce energy costs in many cases.

IMO

SR

When you factor in the wear and tear on an expensive heat pump, COP 1 costs a lot more than resistance electric.

I guess I should have been clearer. What I was alluding to with COP-1 was in fact electric resistance heat at COP-1 and NOT a HP.

SR