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66gsx
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Posts:2
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| 08/09/2009 4:32 PM |
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I've been reading as much as I can on this site and have increased my knowledge greatly but find it is still not enough to make fully informed decisions on the best way to go for my individual application as far as bang for the buck goes.Opinions from the site gurus and anyone with tips or suggestions would help me greatly in steering my decisions.
Let me try and give you as much pertinent info as I can. I live in a 1700sqft chalet style house in southeastern wisconsin. Basically somewhat like a ranch having vaulted ceilings in frm and lvrm and a loft style bedroom, bath, and den upstairs. The house is fully heated by a 64k 95% 2 stage gas furnace which I had put in 10yrs ago. It heats the house just fine and I have no complaints with that but the comfort level in the house is atrocious as you can imagine.
Ideally I would like to install a staple up system that covers the 1200sq 1st level, 200sq of that is frm over crawl space. My main goal is increasing floor comfort and overall comfort in the house and providing anywhere from floor conditioning to substantial heat load depending on what makes the most sense for me in setup costs and running costs.
I have to admit that I was originally turned on to this by the online companies that aren't thought of so highly here years back. I fell in love with the idea of radiant heat, the comfort, the efficiency, the simplicity of the systems, "open direct" you get the point. I told myself when my current gwh needed replacing I would figure something out, well it's leaking and I'm trying to research as best I can.
Some of my guidlines so far are venting through the side of my house, getting rid of my masonry chimminy, and keeping costs reasonable. The polaris cwh is where I was initialy led but seemed too pricey, I then found the aosmith vertex 100 for a bit more of a reasonable price that I wasn't feeling to bad about so my goal became to research the unit as best as I could so I would feel confident about the purchase properly fitting my needs as I would install it immediately and do the radiant part later this year. Well now after reading so much on this site I have discovered what the drawbacks and risks are to the open system, as I knew there had to be something, but am a little concerned about the increase in price now because of heat exchangers and whatever other things I don't know about yet.
I'd love to hear what you guys think for my situation and needs.
mark
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NRT.Rob
Registered Users
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Posts:733
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| 08/09/2009 7:08 PM |
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If you are happy with the fuel economy of your existing heat, floor warming can be done cheaply, but you will need a heat exchanger and I would strongly recommend thermostats with floor sensors. It can be simple as well, but a couple hundred for a basic reset control will make a comfort difference as well.
You might not need a very large unit to provide basic floor conditioning, but if you plan to have actually warm floors that depends on your heat load, and you'll be looking at something more like primary heat in that case. Neutral, but conditioned floors are of course much more comfortable than cold ones, but you won't get toasty feet until you get into a heat load you would want to consider high efficiency equipment for. |
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-=Northeast Radiant Technology=-
NRTradiant.com |
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66gsx
Registered Users
New Member
Posts:2
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| 08/09/2009 8:31 PM |
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Thanks for the response Rob. When you say I wouldn't need a very large unit for floor warming I assume you are talking water heater, but if I am more interested in toasty feet and a more substantial heat load, which I think I am,does your reference to high efficiency equipment still mean tank water heater or are you moving to other options at that point.
I realize the importance of proper planing and design especially as the system would become more of a substantial heat producer for the house but if my options stay in the tank water heater category and being high efficiency I see my choices as limited.
Without trying to sound to naive or oversimplify things I guess my thinking is that I would like to provide as much heat to the floor as possible while trying not to increase my overall gas usage from current levels and letting the furnace pick up the slack where necessary. In other words there's no way I'll ever run out of heat in the house it would just be a matter of which is doing more the furnace or the water heater and finding the balance between the two in terms of comfort and efficiency.
The vertex 100 seems as though it would fit this application, I've read others talk about the Bradford White combi unit but I haven't had a chance to look into price and specs. Whether or not these units are an exact fit for me or not is hard for me to say because there are so many different setups out there but I'm trying to keep in mind that I'm not trying to be solely radiant and loose my furnace because that is not in the budget.
mark
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NRT.Rob
Registered Users
Advanced Member
Posts:733
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| 08/10/2009 11:36 AM |
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There are efficient tank heaters.. I would go with the Phoenix in that case.. but they are in the same price ranges as mod/con boilers. So yes, really your choices are tank or cheap, with some expensive tanks as the exception. the Vertex might be a middle of the road option; hard to say, since they don't tell you what happens to the efficiency as your incoming water temperature rises.
Whether you want to lose the furnace or not, if you want toasty floors you need to deliver enough heat to do that, and you would be de facto radiant at that point. So what you are saying is, you are looking for floor comfort but not toasty floors so you can keep your heat source cheap but improve your comfort: that's viable, I'm just trying to refine your expectation to something more realistic. If a cheaper tank is a good choice for you, it's because you aren't delivering too much heat, and your floors aren't too warm. otherwise it would not be a good choice from a medium term perspective (that is, more heat delivered means ROI on heat source upgrades much faster). |
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-=Northeast Radiant Technology=-
NRTradiant.com |
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Dana1
Registered Users
Advanced Member
Posts:702
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| 08/10/2009 1:49 PM |
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I you're heating the place with a 64K 90% AFUE hot air furnace, a tank HW heater's output is about half that. For the vast majority of heating season hours you're at less than half your full rated-load (your full-rated load is fewer than 5% of the heating-season hours), and that full rated heat load is likely far below (maybe only half) the output of the hot air furnace. Does it ever run continuously at high fire for 4+ hours straight? (I'm guessing 2 hours tops, if you're using overnight setbacks.)
Unless you have the tightest house in N. America, even with a 90% AFUE condensing furnace, by virtue of it's forced hot air distribution system will drive higher air-infiltration losses than an all-hydronic system. It will use 10-15% more fuel than a similarly sized 90% AFUE "right-sized" hydronic boiler based heating system, because hydronic systems don't create those air-pressure differentials, blowing heated air out, and sucking outdoor air in. That means the condensing furnace uses about the same amount of FUEL as a 78-80% AFUE hydronic boiler. (What's in an AFUE test anyway? Don't get me started! ;-) ) A cheap gas-fired tank running flat-out delivers 78-80% in raw combustion efficiency with, less than 2% jacket-loss. If you already have a gas-fired tank, you're already been taking that jacket loss hit (and more), and it won't increase with increased duty cycle on the burner. (But your flue idling losses on the water heater go DOWN with increased duty cycle.) With anything more than a 50% duty cycle you'll be getting ~75% efficiency out of it, but without the induced infiltration loss of forced hot air. Fuel use while relying on a tank HW heater for space heating won't be dramatically more than heating with a 90% AFUE hot air furnace, and in some instances it'll be lower.
Going to with a sealed combustion (not just forced draft) will buy you a 5% cut in fuel use as well, since it's no longer depressurizing the house, inducing a trickle of infiltration for combustion air. Any replacement hot water heater you replace it with will give you better space heating performance if it's sealed combustion, and that's whether you use it for space heating or not(!).
A Vertex 100 or CombiCor running radiant floors could cut your fuel bills by somewhat more than you think. The CombiCor's burner is probably more closely matched to your actual heat load, but it's AFUE is 80-82%- better than a cheapo tank, but not by huge amounts. The condensing Vertex 100 will likely use less fuel then the CombiCor despite being somewhat oversized for the application. (It'll DEFINITELY deliver more DHW than the CombiCor, something to consider if you regularly have multiple shower draws in a row on cold winter mornings.) Also the CombiCor is not sealed-combustion whereas the Vertex 100 is, which makes a difference independent of other test ratings. It's conceivable that a sealed-combustion standard tank would even outperform the CombiCor in a well-designed system, but it would never come close to the Vertex. But a CombiCor makes the system design a bit easier than a standard tank since it has an internal heat exchanger.
The limitation to the radiant isn't likely to be the hot water heater even if you go with a standard 30-40KBTU unit- getting full design-day heat out of the staple up at standard DHW temps is where it's likely to come up short (you can raise the temp, but it'll increase the standby loss.) But that's not a disaster. If the floors are nice & warm, having the condensing furnace cycle on occasionally when it iisn't as uncomfortable as a steady draft and bigger temperature swings, all the while padding around on sub-65F floors. The air temps at which you feel comfortably warm drops a few degrees with radiant too, so if you run the house 3-5F cooler your heat loss is lower, burning less fuel.
If you're going through the trouble & expense of low temp hydronic floors, might as well use 'em. Even with a lower efficiency burner it'll likely be on par with the hot air furnace from a fuel use POV, with a huge uptick in comfort. To find out how close to the actual design-day heat load a standard tank burner is (and something to figure out for future heating system burner specification use), play around with calculator based on systems modeled & tested at the Brookhaven Nat'l Labs:
http://nora-oilheat.org/site20/fsa/FSACalculator_1_1_0_8.zip
For more detail on the systems tested to develop the model, see:
http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf
It'll be more accurate if you can base it on "K-factor", (which would require converting therms or CCF to whatever to gallons of oil, and tracking actual degree-day data) but annual fuel use & location will still be closer than a Manual-J calc. If you're like most people, you'll be surprised how low your design-day heat load actually is compared to the size of your heating equipment. With sealed combustion condensing hot air furnaces the performance penalties for over sizing are low, and 2-3x oversizing, even 4x is quite common. I'd be surprised if yours was more than 2x.
It wouldn't surprise me if you could hydronically-heat the whole place with a 40K-in, 82% burner (a ~33K design-day heat load.) You surely don't need 100K (which would be the input of your dying tank added to your hot air furnace.) 50-60K in a combi will likely suffice for both loads, assuming suffiient tank size. But play around with the FSA Calculator a bit, prove it to yourself. Once you have the radiant in place, a hot water heater will handle the entire load at least 85-90% of the time. If at some point in the future you wanted to retire the hot air furnace, judicious placement of low-temp panels or fin tube baseboards where needed to get more heat into the room on design day can make it a 100% hydronic solution. By the time you burn out your tank, you'll likely know whether or not that's the direction in which you'd like to go, and whether there is sufficient payback in higher-efficiency burners. (With the crash of natural gas prices this year it's a bit harder to rationalize condensing equipment pricing on the fuel savings differential alone.) If you go with a cheap tank, DO use external heat exchangers for the DHW- risking your health to save a few hundred or even a few grand just isn't worth it. |
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