who knows about home heating?

[rh71]

Currently making plans to do a 2nd-floor dormer (4 beds, 2 baths) to our new-to-us ranch. 1st Fl (and basement) currently uses 5-zones of baseboard heat and an older system with a boiler which won't support a 2nd floor in addition.

Options are to add an additional boiler for just the 2nd floor or upgrade this one entirely for $2k more than the price of adding 1 more boiler. Many contractors are saying this original is perfectly fine for its current purpose and doesn't need replacing. If we don't replace, we have to maintain both and that's always a higher risk.

Other, more important, question is - do we do more baseboard for the 2nd floor or do we go with a a complete system replacement - a "hydronics" system which is forced hot air from vents that the central air will use? Many contractors are high on hydronics because of efficiency (and ease to install) but one really put it to question when he mentioned hot air is not efficient... heat rises, and the vents are up top because that's where the AC will be coming out. One guy's response to that was the return vent makes all the air move around regardless. Also hot air makes it too dry. In my experience with winter & heat, it's already really dry with baseboard.

There's also the question of which is more costly... one has said baseboard is very expensive to put in and another guy today said hydronics is more expensive. In my amateur-ish opinion, all the high-end and newer homes use hydronics, presumably because it makes it look clean (no baseboard). That's a factor for us too but if it sucks, then no.

If it matters, we use gas, not oil. What say you?

 

[Paperdoc]

With a forced-air system properly designed, the "heat rises" argument is just about worthless. It is true that warm air rises. In a room with very little moving air, the temperature near the ceiling will be warmer than near the floor, but you are on the floor. BUT add a fan that supplies moving air to the room and them removes (though return ducts) air to be recirculated, and you no longer have that situation. The air movement very easily carries the warm and cool air around the entire volume of the room. You can demonstrate that easily by taking air temperature readings in a house with forced air heating. The temperature differences around the room will be small. In fact, you're more likely to find the differences related to other factors like the proximity to walls and windows, which are either heat sources or heat loss routes.

I am not clear whether you already have a forced-air system that ONLY functions for a central air conditioning system, and not to provide heat. If you do, then expanding that to an additional floor is a big change, and that entire system would need review and possibly upgrading just to expand providing the air conditioning function without any heating. If you were doing that job, you might find it more effective to revise the whole system to encompass both increased cooling and heating capacity. That might well take you out of hydronics and into a more conventional gas-burning forced-air furnace with added air conditioning.

I am not sure why hydronics is the recommended technology. I presume that, by that term, you mean a system which burns gas to heat water which is then circulated through the house through piping. At some points there are heat exchangers that heat the air. In fact, that is what your baseboard system does now. But you seem to be proposing that at least part of the new system (the new floor?) would instead use heat exchangers mounted inside new or existing ductwork for a forced-air system, and it is that stream of air that would be heated. If your plan is to create a new air conditioning forced-air system for the upper floor and then supply heat for it from the basement or main floor, I can understand why small-diameter pipes from one floor to another might be preferred over large air ducts. An alternative, though, might be to mount a more traditional furnace type on the upper floor itself, separate from the system that heats the main floor. On the other hand, if your are talking about expanding an existing system that serves the main floor, see my comments above about reviewing it thoroughly.

Any system that provides heat only will result in "dry air". An air conditioner, if it is used only to cool down to the target temperature as most are, won't do that - it actually increases relative humidity by reducing air temperature without removing much water. Air conditioners DO remove water and generate condensate IF the air is cooled enough to become saturated - that is, the air exiting the cooling coils is nearly 100% Relative Humidity, but that is not considered "dry air".

Any forced-air system CAN have added to it a humidifier that evaporates water into the moving air in the ducts to increase the Relative Humidity. It actually is surprising how much water is needed for that, so a good humidifier design is important if that's what you want. Without forced air systems (for example, with baseboard heaters as you now have on the main floor), your option is a stand-alone humidifier appliance that usually includes its own small fan to help move air through.

Whatever you do, I really recommend that the heating system be "high efficiency". The furnace is a more complex design (and hence more expensive) that involves more than one heat exchanger to maximize extraction of heat from the hot combustion gases into the real heat transport medium, be that forced air or water in pipes. Because of that, there is normally an induced draft fan - that is, a fan the sucks the cooled combustion gases through those several heat exchangers and blows them outside through a duct. That duct may not look like a common flue pipe at all - mine looks like 2" black plastic drain piping and it exits out the side wall of the building, not up through a chimney. Such systems often quote efficiency (that is, how much of the available heat from combustion actually is retained and delivered into the house) well over 90%. The savings in fuel costs usually can pay for the increased cost of the high-efficiency furnace design in 5 to 10 years.

 

[rh71]

^ thanks for the insight. What about a room with its doors closed while the return vent is out in the hallway? I would wager that the room still gets warm of course but is it efficient?

What costs more to install in our case? If it is similar, we'd just take the dual-job vents. The situation is we have central air already with ducts, but the 2nd floor addition means we'll also need a 2nd AC unit (new zone) and new ductwork. This is where we decide if the heat will go through those new AC vents as well... and whether we want to convert the 1st floor system into using the AC vents (pre-existing) and throwing hot air through them. You were correct that we "already have a forced-air system that ONLY functions for a central air conditioning system, and not to provide heat".

We've seen a handful of contractors and all but 1 recommended a hydronic system - and it seems there were variations of it. Their idea seemed to be we'll have 2 AC units outside, then a hydronics system for the heat... or maybe you can explain it better...

If your plan is to create a new air conditioning forced-air system for the upper floor and then supply heat for it from the basement or main floor, I can understand why small-diameter pipes from one floor to another might be preferred over large air ducts.

Yes but as I understand it we'll be putting in a 2nd CAC unit outside for this upper floor. Now I'm also reading hydronics does both... without the need for the big unit outside? Too many people are telling us different things so it's been confusing - what would you recommend for us?

have:
1 CAC unit outside (12 years old - can replace if need be) providing for air conditioning through vents to basement and 1st fl.
1 burner (and hot water tank) with 5 zones providing for heat through baseboard in basement and 1st fl.

need:
heat and CAC in all 3 floors. (~2600sq ft home) in the most efficient manner. What hardware goes in or comes out is not a huge factor to us as long as it's the best way of going about it... and the extra costs are minimal.

 

[dullard]

The only way I'd go: two completely separate systems for two different floors.

In summer, you'll need to cool the top floor far, far more than the main floor. The top floor is hit by heat on all sides, from the roof, and from any heat rising from the main floor. By keeping the top floor cool, the main floor is almost cooled automatically (it will be cool on top and bottom, so it only has a few walls to be conserned with). With one system you have to close almost all cool air to the main floor and try to force it all to the top floor. That is highly inefficient and difficult.

In winter, it is the same situation, but replace heat with cool. Plus, with an addition like what you are planning, your top floor insulation is probably quite different from your bottom floor insulation.

Basically, your top floor needs are completely different than your main floor needs. Why crudely force one system to do both? You'll never get good temperature control and you'll always be trying to manually close off vents (or curse that you can't open them wider than fully open). Two systems, one for each floor solves that flawlessly. Each floor has its own thermostat and its own heating/cooling. Each floor is exactly the temp that you want.

Plus, you get the flexibility to save money by having programable thermostats shut off a floor when you don't use it. People often aren't on the top floor during the day, and they often aren't on the main floor at night.