Radiators vs. Forced Air
We are in the process of converting an old oil boiler to a natural gas system in a relatively small 1500sqft cape style house. We are trying to decide whether to keep our hot water radiators, or switch to forced air. We already have a central air conditioner, so it would be cheaper to use air by just adding a furnace to the air system. However, I have heard from many that radiators are the "best" heat source.
We are looking for a 90-95% high efficiency system either way, and the option for forced air is a modulating btu/fan speed system with a direct intake from outdoors. The technician who quotes us explained that the common criticism of forced air being dry and drafty would be mitigated by having a system like this. He also explained that potential problems with water circulation would not be a concern with forced air.
I grew up with a forced air system (granted this was 15 years ago and not a high-tech system like this), and it is indeed dry and dusty. Can anyone recommend whether we should stick to hot water or switch to forced air? Thanks!
Where is the air handler for the cooling? Above? If so that would be the least comfy way of doing it, trying to blow down. Just can't beat hot water heat comfort.
Chances are your 95% efficient condensing boiler will be in the 82-85% efficient range with your radiator setup. Hot water heat is far more comfortable but with cast iron radiators your efficiency is going to suffer so it is a trade off. You could redo the piping and install radiant in floor or supine ring the radiators but you are pricing yourself out
Well Ive Lived with both and truly love my current high eff. water boiler. Though it is a high eff. boiler, that is derated, as once the water breeches the condensing temp.(aprox. 140') the eff. falls off Im guessing aprox. 5 to 7%. The convectors are slow acting which gives a nice comfort level. Though thats all likely an opinion ? If given a choice I'd heat my home with infloor hotwater which would be most economical as then the water temp. can be under 100' thus keeping the high eff. boiler at a 90+ rate.Certainly with the A/C allready ducted as you say you have inplace,:.02: easy isnt allways best though possibly cheap and easy
The air handler is in the basement.
The way the technician explained it was the comfort of radiant heating is due to the slow, even heat. The modulating forced air furnace, he explained, mimics this because it stays on evenly and low, rather than shutting on and off abruptly and infrequently.
Does that make sense?
Thanks for the reply.
Yes it does make sence though it tries to come close to mimic the effect of raidiation
If I had all the money in the world I would love to have heated floors! Sadly our budget doesn't allow.
Seems like you are suggesting that forced air would be more efficient, yes? But that radiators are more comfortable?
If this modulated forced air system were as comfortable as radiant, due to the slow, constant emission of heat, then it would be more efficient, and pretty comfortable, and cheaper. This just seems too good to be true, what am I missing?
Thanks for the suggestion.
What kind of radiators do you have? The heavy cast iron ones or the baseboard fin type?
They are all baseboard fin radiators, of one type or another. Not big the old-fashioned iron things. Im not sure what they are called, but most of them are the kind where theres a wide inset opening in the wall, the hot water pipe/fins running along the bottom, and its all covered by a metal plate with vents in it.
I know the type of radiators that you're talking about. You don't say where you live or what kind of temperatures that you experience during the winter. This information would help in suggesting what might work better.
With the existing air conditioning system already in place and being an option of installing a furnace instead of the air handler that is there now I'd suggest that you consider carefully how that duct work is routed to each room of the home. If it was installed and set up specifically for air conditioning only the placement of registers for both supply and return air might not keep you as comfortable in the heating season as you'd hope. BUT, this all depends on how it was installed originally.
The original hot water registers were designed and "more than likely" sized for the coldest winter days with a water supply temperature going to them of usually 180°F. Putting in a high efficient boiler (90%+) and setting it to run at this high temperature all the time would not get you the rated efficiency as mentioned by someone else. But, the high efficient boilers come with what is called a reset control normally built into their controls. This allows them to lower their output temperature as it gets warmer outside. This function allows the boiler to fine tune itself to the exact heating needs of the home at any given outside temperature.
In the "perfect" hydronic system, or any heating system for that matter, you will be most comfortable if the heating system is always (24/7) putting in the exact amount of heat needed. A modulating high efficient boiler does this by varying the output water temperature it is delivering to the radiators.
Your specific house already has two completely different comfort systems. If you abandon the hot water system and modify the air conditioning system to do both you will have the costs associated with demolition and removal of the hot water system and all of it's components either now or in the future. That cost should be factored into the decision process. Leaving those recessed wall mounted units in place (most I've seen are always mounted in an outside wall) will leave an uninsulated spot in your exterior walls. Somewhere down the road you'll probably want to remove them and patch the walls..... An expense. Removing all the piping is an expense. If the newly modified forced air system keeps you perfectly comfortable all is fine. If you find you're uncomfortable in certain parts of the house then there might be the expense of modifications to that system to improve comfort. Note: A fully modulating furnace does not automatically make for a perfect comfortable home. The duct work and register placement has just as much to do with it and in some cases everything to do with it. :whistle: It's one of the potential scenarios that fit my tag at the bottom of my post.
What do I suggest? Whoever you have look at your situation to give you pricing, make them prove and guarantee that you'll be just as comfortable as you are now once their system is installed. Any professional should be doing heating load calculations room by room (to verify the radiation in that room will put out enough heat) and duct work calculations to verify the duct work is adequate to supply both air conditioning and heating comfort year around.
From what you've said, and from this vantage point, I'd suggest you go with the high efficient boiler for your heating. The modulating high efficient boilers, with the correct installation and controls, can supply lower temperature water that will allow it to condense and achieve it's rated efficiency a majority of the time. When and only when the outside temperature gets low enough that the lower water temperature can no longer keep up, the boiler can be told to supply high temperature water. This can be done with the use of a two stage thermostat. This higher temperature can be adjusted so even it only gets as hot as it absolutely has to.
Just my thoughts, just my opinion. Am I right or wrong...... I'm not there and I didn't do the calculations to see if it'd even be cost effective. What I do feel is that you'll more than likely be a lot more comfortable with this option, but even that "feel" is not based in facts based on having been there and assessed your home and it's existing systems.
Radiant or Forced Error
For the most part, homes in colder climates have been heated with hot water. Forced Air became popular as A/C began to be added to homes and it was a cheap, easy way to get heat at the same time by just adding a furnace to the system.
There's no way that even a modulating furnace is gonna compare to a properly installed hot water system. Hot water radiators heat two ways: first, they produce heated air by convection, but more importantly the heat surrounding surfaces by radiant heat. Radiant heat rays travel in all directions as they heat surfaces (including your body), thus, they produce a much more even and comfortable heat. A furnace only heats air which must in turn heat objects. That's just the opposite of how it should be done. That's why it's "forced error".
Consider this also: if you keep your radiant system, you can gradually phase in even more efficient emitters like radiant floors over a period of time. Never gonna do that if your remove it.
Depending how your system is piped, you could possibly put TRV's (thermostatic radiator valves) on each rad giving individual control.
"firecontrol" has given a lot of good info about modulating boilers and outdoor reset. Take time to research and digest it.
Please, don't let anyone talk you out of your radiant. They simply don't know what they're talking about.
Just so you know: we do forced air as well as hydronics because that's what's already out there. But, I would never recommend removing a good hydronic system for forced air.
Originally Posted by andrewcroce
No one wants to heat a home with forced air. Moving air does not increase comfort unless you are trying to cool off. Think wind chill. The simple reason that 98% of the US heats with forced air is because we build most of the homes now lived in after Mr. Carrier popularized the compromise heating system, which included AC.
Though fin-tube baseboard is not radiation (convector as suggested) is is quite and usually well placed at the perimeter of the house where heat escapes most and discomfort starts. A condensing boiler will condense a good part of the heating season with ODR as suggested by others and at any rate will maintain an 86% combustion efficiency regardless of water temperature delivered. This is higher than any conventional boiler and also gives you the added savings of sealed combustion (closing down the chimney if you add domestic hot water).
Remember what they install in a trailer house when they start talking about how much better forced air is.