Hello all,
I'm new to this forum. Stumbled across it while reading up on radiant heating and am hoping some folks here might be able to lend advice.

I've got a 1923 built bungalow-style home in the Seattle area that currently uses hydronic radiant baseboard heating fed by an ancient boiler (likely an old oil boiler converted to natural gas) and uses a standard natural gas hot water tank for the potable water. I'm in the beginning stages of planning a renovation to the house (it's in terrible shape) and would like to keep some form of radiant heating (either wall, underfloor, or baseboard). Frankly I don't want to have to consider running air ducts for forced air and I like the feel of radiant heat...except that my house has more hot air escaping than a politician's mouth. Anyway, I've got a number of what I hope are basic questions that I need explanations for that I think will make it a lot easier for me to understand a lot of what I'm reading around the web about my options. On to the questions

1) My hot water heater is about done for. I'd like to replace it in the short-term and for years had planned to replace it with a tankless hot water heater. I'm a single guy living by myself so hot water tanks are pretty much a waste of money. That said, I am trying to be forward thinking about it and I get the impression that most people aren't in favor of using tankless hot water heaters when also using a boiler (or mod/con). However, I don't think I understand what the superior options would be in this case.

2) This house needs a lot of work and I'm trying to figure out what I can afford and in what phases. Is it possible to replace the boiler now and continue using it with the existing radiant baseboards and switching it later to underfloor radiant? Further, I am looking at the option of jacking up the house to pour a proper foundation for the house (it's post and pier right now and the whole house shakes when the washing machine runs) in which case I'd create a daylight basement. If I went that route I'd like to also have the basement as an additional radiant zone (with the heating in the poured concrete floor). I'm guessing that I probably need to have a solid decision on that before replacing the boiler, right?

3) As mentioned above, this house has a ton of air leaks. I expect that I'll be reinsulating it and will definitely be replacing all of the single pane windows. I understand that a reputable company selling a boiler will do a computer-generated heat-loss analysis, but how is that possible until I reinsulate and replace the windows? I guess I'm trying to understand which step has to come first. I just prefer to plan things out ahead of time so I know what the costs will be.

4) Given that I'll be sealing up the house quite a bit, it would seem that I need something to keep air fresh in here. The house has nothing right now other than the many leaks. From what I've read it seems like I'll have to use some sort of air exchanger (believe they call them HRV's and ERV's). It would seem this will then require the ducting that I was hoping to avoid.

5) Like I said, I live in Seattle so there's not a great need for air-conditioning as we get like one or two weeks a year that get uncomfortable in the summer. That said, I'm wondering what my options are for cooling beyond ceiling fans and plug-in air conditioning. I've read some companies advertising that their radiant products also do cooling, but that just sounds like a disaster waiting to happen given the condensation that would build up in a place like western WA where we generally have moisture in the air year round.

6) Do mod/cons or boilers vent to the side of the house? The current boiler vents up a chimney which runs straight up through the kitchen. I'd like to remove that chimney so that I can open up the kitchen and the space above it on the 2nd floor.

I apologize if any of these seem like uneducated questions. This isn't really an industry I have any background in and I'm simply a little overwhelmed with all of the different terms and options. I've been slowly educating myself on the various things I need to do for this remodel over the past few years. So I appreciate any help anyone can lend here.

the order is: Fix the house, then fix the systems, if at all possible. Doing it the other way around results in more money up front and less efficiency down the road.

if you seal tight you will need to vent right, as they say. This is good. IAQ ductwork is not large.

mod/cons direct vent through the side of the house.

No mainstream reputable company I know of right now advertises for radiant cooling. There are some "limited free cooling" claims out there, but you have to stress the "limited" to the point of "negligable" and to do it you have to install an open freshwater system (no separation between heating and domestic) which is a horrible idea.

That said, we are starting to design true radiant cooling systems. They are limited in output and it is a "brave new world" in the residential market. However with a ventilation system doing dehumidification, it is possible to design true radiant cooling systems. Very few people are actually doing so, as far as I know though. If you don't need much, it can work well, but unless you're already doing a heat pump like a geothermal unit or a Daikin Altherma, if you only need a few rooms of cooling "window shakers" are probably more cost effective. Chillers for water cooling systems are something like $4k to $5k by themselves at this point in time... unless someone else knows a cheaper option!

A couple of comments: Heat loads in Seattle are typically pretty low (the 97.5% outside design temp for Seattle-proper is 26F,and most locations within King County are within a degree or two of that. Unless this is an unusually large bungalow, with some air-sealing and spot insulation remediation, it's likely that your design-day heat load will be under 20KBTU/hr, and even a mod-con would short cycle. A hot water heater with 50K+ of burner (condensing or otherwise) would very likely be able to heat this place. For reference, I too live in a 1923 bungalow that I've tigthened up a bit, but with known gaps in the insulation, and design-temps 22F colder than Seattle, and my heating/hot water combi system never exceeds 50K of output, even with all zones calling for heat , with the shower running (helped by the thermal mass of 48gallons of buffer and a drainwater heat recovery heat exchanger.)

My design condition load is ~30K, and will be ~25K after I rehab the attic rooms with more air-sealing and better insulation. Total conditioned space not including the basement is ~2000', but the ~1600' of full semi-conditioned basement stays around 65F-66F all winter, and can be considered conditioned space from a total heat loss point of view.) If your house is at all similar in size, A mod-con would likely be wasted at your house, since even the smallest would be in cycling mode far more of the time than in modulating mode.

Since you sound like you're in the position of having to pull the trigger on a new hot water heater before the rehab, you should seriously consider a combi. If you have good billing information using your existing system(s) and can correlate it with degree-day weather data for your exact zip code (or very nearby) to the exact billing dates, it's pretty easy to tell if you'd be able to heat the place with a particular combi unit even before rehab. I suspect any of the commercially available tank-based combi systems would work, but take the time to calculate the heat loss on the place anyway, and pay attention to the room-by-room losses, and the available baseboard. (You may have to crank up the temps on the combi to get enough heat out of baseboard before tightening the place up.)

Despite the rainy climate, summertime dew points (a measure of the absolute, not relative humidity) in Seattle rarely exceed 60F and are usually in the 40s & 50s F. Condensation would NOT build up with a radiant cooling system the way it might in the more humid mid-atlantic seaboard or gulf-coast states (where dew points stay in the 60s & 70s for months). The sensible-cooling loads are also pretty small, and nighttime ventilation + solar shading of windows strategies work well almost of the time (particularly in reasonably tight houses with a modicum of interior thermal mass.) But active cooling using radiant floors is still a very reasonable option- the floor temps would rarely need to drop below the dew point (maybe one bizarrely muggy week per decade.) Dew points in the mid-60s where condensation from radiant cooling becomes a real issue are so rare in Seattle that it makes the weather-geek news: http://www.komonews.com/weather/blogs/scott/103950144.html

The Daikin Altherma is quite hunk of change compared to a gas-fired combi, but very likely to be reasonably sized for your peak heating loads. The Altherma puts out about ~25KBTU/hr @ 25F outdoor temps, ~20KBTU/hr @ +5F. At western WA utility rates it would be much cheaper to operate than a gas fired system, but it won't necessarily be net-present-value positive in less than a 25 year time frame unless you were also considering central air conditioning as a separate system.

Dana,
Thanks for the feedback. There's a lot there that's over my head (and acronyms that I'm still not familiar with), but basically what I understood was: "Combination Boiler is a better option than a Mod/Con given the size of the house". That pretty much summarize it?

You are correct that my bungalow is fairly small. It's just shy of 1,800 sq ft. right now. I estimate that creating a basement would add around 800 sq ft to the footprint.

I hadn't looked a great deal into combi options because I mistakenly took them to be variations of what radiantec offers (which everyone seems to hate btw)...looks like it's a similar concept to them, but uses a boiler instead of a tank. I just did some reading on combi options and a couple of questions come up:

1) It appears to me that a combi setup is an open cycle, right? In other words, the water comes in the house, is heated, cycles through either the house heating circuit or DHW and goes back out. Or is the house heating a closed circuit? One benefit of my neighborhood is that the houses all have flat rate water supply (I guess they didn't want to add meters to all these old houses), so water-usage levels are not a cost consideration though obviously I want to be responsible about my usage.
2) Would a combi be able to be used with either baseboards or infloor heating? Again, trying to think ahead to when I would preferably get rid of the ugly old baseboards for some heated floors.
3) Is it possible to get a strong flow-rate for the DHW while sizing a combi properly for the home heating? Right now there are two bathrooms, and if I do pour a basement, I would add a third there.
4) Will a combi support multiple zones? I have two floors now and the basement would be a third zone if I built it out.
5) You mentioned the Daikin Altherma is quite a bit more expensive. What does that mean really? One thing I don't really have a handle on is what the costs are for the various options (i.e. mod/con, combi, etc.). I have been able to price out some tankless hot water heaters I'm interested in, so I understand what kind of range I'm looking at for those. But for what you're talking about, what kind of range should I expect for costs?
6) I have the option of either electric or gas units. I get the impression from your post that electric is a more cost-effective solution...am I reading that right? I would've thought gas would be the better option (though I've admittedly never compared the costs of the two). It just always seemed to me that gas would be a more efficient process for eating on-demand water supplies.
7) In a lot of mod/con setups I've read about something that monitors the outside air temperature and adjusts the boiler accordingly to provide the level of heat desired. I can't recall the name of that, but is it something that should/can be considered with a combi?

Thanks for the explanation on dew point. I understand dew point but nothing about radiant cooling specified dew point (only mentioned high humidity areas) and most specifically illustrated the examples as Eastern Seaboard vs Arizona (no one ever thinks about us up here in lonely PNW).

Posted By NRT.Rob on 20 Jan 2011 09:32 AM
the order is: Fix the house, then fix the systems, if at all possible. Doing it the other way around results in more money up front and less efficiency down the road.

if you seal tight you will need to vent right, as they say. This is good. IAQ ductwork is not large.

mod/cons direct vent through the side of the house.

No mainstream reputable company I know of right now advertises for radiant cooling. There are some "limited free cooling" claims out there, but you have to stress the "limited" to the point of "negligable" and to do it you have to install an open freshwater system (no separation between heating and domestic) which is a horrible idea.

That said, we are starting to design true radiant cooling systems. They are limited in output and it is a "brave new world" in the residential market. However with a ventilation system doing dehumidification, it is possible to design true radiant cooling systems. Very few people are actually doing so, as far as I know though. If you don't need much, it can work well, but unless you're already doing a heat pump like a geothermal unit or a Daikin Altherma, if you only need a few rooms of cooling "window shakers" are probably more cost effective. Chillers for water cooling systems are something like $4k to $5k by themselves at this point in time... unless someone else knows a cheaper option!

Thanks Rob.

Glad to hear that venting con go out the side of the house. What size does IAQ (assuming that's Indoor Air Quality) piping run typically? We talking a 6" diameter pipe? Smaller?

I am leaning away from a cooling unit. My main concern is the top floor which is unbearably hot in the summer right now (with no headroom for ceiling fans). My hope is that a remodel with proper insulation and new windows the upstairs would be bearable without any AC...but I'm just not positive. One slope of my roof faces south (and that slope has dormers upstairs) so that sun just beats right into that side of the house. The other side of the house is generally pretty bearable in the summer, particularly with the ceiling fans I've installed. It's difficult to judge however, since only one window per room opens right now (all the others are painted shut by a previous owner). So once the heat builds up in the house, it's difficult to get rid of at night when temps drop.

Posted By justin_aws on 20 Jan 2011 10:34 PM
Dana,
Thanks for the feedback. There's a lot there that's over my head (and acronyms that I'm still not familiar with), but basically what I understood was: "Combination Boiler is a better option than a Mod/Con given the size of the house". That pretty much summarize it?

You are correct that my bungalow is fairly small. It's just shy of 1,800 sq ft. right now. I estimate that creating a basement would add around 800 sq ft to the footprint.

I hadn't looked a great deal into combi options because I mistakenly took them to be variations of what radiantec offers (which everyone seems to hate btw)...looks like it's a similar concept to them, but uses a boiler instead of a tank. I just did some reading on combi options and a couple of questions come up:

1) It appears to me that a combi setup is an open cycle, right? In other words, the water comes in the house, is heated, cycles through either the house heating circuit or DHW and goes back out. Or is the house heating a closed circuit? One benefit of my neighborhood is that the houses all have flat rate water supply (I guess they didn't want to add meters to all these old houses), so water-usage levels are not a cost consideration though obviously I want to be responsible about my usage.
2) Would a combi be able to be used with either baseboards or infloor heating? Again, trying to think ahead to when I would preferably get rid of the ugly old baseboards for some heated floors.
3) Is it possible to get a strong flow-rate for the DHW while sizing a combi properly for the home heating? Right now there are two bathrooms, and if I do pour a basement, I would add a third there.
4) Will a combi support multiple zones? I have two floors now and the basement would be a third zone if I built it out.
5) You mentioned the Daikin Altherma is quite a bit more expensive. What does that mean really? One thing I don't really have a handle on is what the costs are for the various options (i.e. mod/con, combi, etc.). I have been able to price out some tankless hot water heaters I'm interested in, so I understand what kind of range I'm looking at for those. But for what you're talking about, what kind of range should I expect for costs?
6) I have the option of either electric or gas units. I get the impression from your post that electric is a more cost-effective solution...am I reading that right? I would've thought gas would be the better option (though I've admittedly never compared the costs of the two). It just always seemed to me that gas would be a more efficient process for eating on-demand water supplies.
7) In a lot of mod/con setups I've read about something that monitors the outside air temperature and adjusts the boiler accordingly to provide the level of heat desired. I can't recall the name of that, but is it something that should/can be considered with a combi?

Thanks for the explanation on dew point. I understand dew point but nothing about radiant cooling specified dew point (only mentioned high humidity areas) and most specifically illustrated the examples as Eastern Seaboard vs Arizona (no one ever thinks about us up here in lonely PNW).

It's not about the size of the house, but the size of the heat load.  If you moved your house to Saskatchewan your peak heat load would nearly double, and a mod-con would look like a good option.  If the lowest-modulated output of the boiler is a large fraction of your peak load some of the benefits of the more-complex & expensive modulating-condensing boiler aren't there, since it spends most of it's operation just turning on/off like a non-modulating boiler.  Tank-type combis use the thermal mass of the water in the tank to keep efficiency high despite mostly bang-bang on-off operation of the burner, whereas you'd have to guarantee some minimum thermal mass of the system to keep a non-modulating mod-con optimally efficiently.

In order:

1: Open loop systems are a TERRIBLE idea.  Tank-type hot-water heaters with internal heat exchangers isolating the potable from the heating system is what you're after, be it a  Versa  on the higher-end or a BW Combi-II a bit futher down. There are others, that perhaps some of the pros here might recommend.

2: The combis would be able to run either baseboard or radiant floor, but you may have to crank up the temps a bit if you don't have sufficient baseboard length to deliver the heat to the rooms at domestic hot water temps. Most fin-tube baseboard heating systems are overdesigned anyway, and don't NEED to run with 160-180F boiler water, and would do just fine at 140F (which is low enough to be damaging to old-school boilers and masonry chimneys from a condensation point of view, but also low enough to get 90% out of a boiler/combi designed to take advantage of condensing moisture out of the exhuast.)

3: Tank type combis have EXCELLENT flow rates on the hot water, unlike many tankless HW heaters.  You may want to up-size the gallons if you expect to be running 3 showers at the same time though.

4: Tank-type combis readily support multiple zones (or even micro-zoning), even better than low-mass mod-con boilers, since the low mass boilers can short-cycle on zone-calls if the heat load of the individual zone is small. (The solution is usually to add a buffer tank for more thermal mass, but the combi is already inherently buffered.)

5:  An Altherma is likely to be north of $15KUSD, maybe north of $20K installed (maybe NRT.Rob can jump in here.)  A combi will be less than $10K, maybe even less than $5K installed if you went with a Combi-2 or similar, depending on how awkward it is to retrofit.

6:  Electric in general is NOT a more cost-effective solution, unless the elecric unit is a heat-pump with an average coefficient of performance "COP" of better than 2.  The Altherma is electric, yes, but will average COPs better than 3 in your climate.  The COP is a multiplier- for every unit of energy put into the thing, it delivers more energy out. A COP of 3 is sometime 300% efficient in terms of energy use.  A resistance-element heater is limited to 100% (but is far less than that from source-fuel to load, due to the generation & grid losses.)  To calculate it all correctly you need to be able to convert the efficiency x fuel cost for the gas vs. electric units, but while it's usually pretty easy for a 90% efficient gas unit to compete with 100% efficient resistance electric  in $/BTU-delivered, the converse is true when looking at a 300%+ efficient heat pump.  But without the actual utility pricing we can't say for sure.

7: The term you're looking for is "outdoor reset".  It's primary function with a mod-con is to be able to minimize the heating water temperature, which maximizes the amount of condensing-heat it can extract from the exhaust stream, and to modulate the output to track the load for longer, more efficient burns (which you almost surely can't do with a mod-con running multiple zones in your house & climate.)  A third benefit is that it delivers a more even room-temperature, but that's much less of an issue once you've gone to radiant floor.  It's possible to buy thermostatic mixing valves that respond to outdoor temps, but I'm not sure it's worth the expense in your case.  (I'm running retrofitted radiant floors at my place with DHW temp water, no outdoor reset- it's still pretty damned nice!)

I think of you in the PNW quite often- I'm a native, and visit relatives there every summer escaping even the modest humidity of New England.  Summertime dew points here average in the low-mid 60s, but reguarly hit mid-70s during occasional heat waves.  The 90F+ temperatures of early July last year in the Puget Sound region were downright refreshing compared to 85F in MA with dew points in the low 70s.

Dana,
Again, thanks for taking the time on another in-depth response. It's a great help to me. I'm not really set on any one thing, prefer to understand the +/- of all the options and then make a decision.

The Altherma is definitely out at that range. $5K-$10 is about what I was expecting to shell out for the boiler replacement plus I expected another $1500 or so for the tankless (plus installation costs are rumored to be outrageous here depending on current setup). I think I'll definitely lead to the combi boiler option and I'm glad to hear confirmation that the Open Loop systems are a bad idea. With these tank-type hot water heaters, is it accurate to assume that the amount of hot water available for residential use (say a shower, bath, or dishwasher) at a given time is equivalent to the size of the tank? I read the link you provided on the Combi II and it seems like the tank itself is segmented so that part of it is for residential and part of it is for the home heating. Or does the system replace the hot water as quickly as you use it during a shower and, effectively, act like an unlimited hot water supply (assuming you're only running a single shower, washer, etc. at a time)?

I don't expect to be running two showers at a time, let alone three, so it sounds as if a Combi II or smaller might be sufficient. Now that I have an idea of what I'm looking for I can start reading up on models and calling local vendors for pricing and options.

And I understand completely on the New England summers. All my relatives live back east. Attending June weddings in the Florida keys in 100-110 degree weather with nearly 100% humidity was brutal.

Thanks again for all the input. I have a feeling I'll be visiting these forums some more as I plan out the other aspects of remodeling this place.

Have you considered a ductless mini-split heat pump?

You could go to a minimal water heating system that would service your hot water and peak radiant needs while running the ductless mini-split for general heating and cooling. If you haven't seen them before, the ductless minis are air source heat pumps with connections for up to four "wall units". The structure modifications are minimal as you only need about a 3" hole to come into the house at the wall unit locations. You could put a small wall unit (9 kBTU) in each bedroom (two?) and a larger one in the main living area to temper it. Since they have four connections, you would have one in reserve for your basement remodel. $7,500 for the system and three wall units..

This way, you could get heat pump efficiency for both heating and cooling while retaining the traditional nature of the radiant in specific areas like bathrooms or whatnot - as much or as little as you wanted to keep/install. This should put the cost of your hot water unit way down.

not necessarily. the cost of upsizing water units is incremental. Once you've decided to put one in, making it bigger doesn't jack the price up very fast.

I am getting much more interested in conversion of typical or new heat pump air equipment to hydronics. is anyone aware of any condensers or heat pumps that won't void the warranty if you size a brazed plate heat exchanger for them instead of a duct coil?

Posted By justin_aws on 21 Jan 2011 08:54 PM
Dana,
Again, thanks for taking the time on another in-depth response. It's a great help to me. I'm not really set on any one thing, prefer to understand the +/- of all the options and then make a decision.

The Altherma is definitely out at that range. $5K-$10 is about what I was expecting to shell out for the boiler replacement plus I expected another $1500 or so for the tankless (plus installation costs are rumored to be outrageous here depending on current setup). I think I'll definitely lead to the combi boiler option and I'm glad to hear confirmation that the Open Loop systems are a bad idea. With these tank-type hot water heaters, is it accurate to assume that the amount of hot water available for residential use (say a shower, bath, or dishwasher) at a given time is equivalent to the size of the tank? I read the link you provided on the Combi II and it seems like the tank itself is segmented so that part of it is for residential and part of it is for the home heating. Or does the system replace the hot water as quickly as you use it during a shower and, effectively, act like an unlimited hot water supply (assuming you're only running a single shower, washer, etc. at a time)?

I don't expect to be running two showers at a time, let alone three, so it sounds as if a Combi II or smaller might be sufficient. Now that I have an idea of what I'm looking for I can start reading up on models and calling local vendors for pricing and options.

And I understand completely on the New England summers. All my relatives live back east. Attending June weddings in the Florida keys in 100-110 degree weather with nearly 100% humidity was brutal.

Thanks again for all the input. I have a feeling I'll be visiting these forums some more as I plan out the other aspects of remodeling this place.

The burner on a Combi-II is probably at least 2x your heat load (probably 3x after you insulate & air-seal), and 2x bigger than the burners of most standalone tanks, so if anything you'll have MORE hot water capacity than with a standard tank of comparable volume most of the time, or maybe about the same capacity when the heating zones are all calling for heat.

DO consider going  with a condensing combi vs. a lowest-cost forced-draft combi. They tend to be quieter, better insulated, and will use only ~3/4 the fuel.  It's worth getting a quote, anyway.  The smallest-burner 55 gallon Versa (PHE130-55) has a bigger burner than the Combi-II, and condensing heat exchanger, and a more sophisticated control scheme.  (The local Heat Transfer Products rep in Seattle could probably give you a ball-park price on it, &/or recommend an installer: Christa Peterson [email protected] T: 206-767-7140)   If it's only a a couple grand more cash up front there's some economic argument to be made for it on efficiency, but from a user point of view it's better.  You'd have enough burner to be in "endless hot water" mode for at least one shower + heating system operation at any time, yet it will modulate the fire down to about 45KBTU/hr when hot water & heating loads are light, which is most of the time.  At minimum fire it's probably still 1.5-2x oversized for your post-rehab peak heating loads, but the thermal mass of the 55gallons of water keeps it from lossy short-cycling. It's probably overall a better match for your combined heat/hot water needs, even though you probably could get by with a Combi-II.  If you'd be burning 1000 therms/year of gas with a Combi-II, you'd be looking at  750-800 therms with the smallest Versa, and it would likely pay the upfront cost difference in fuel savings over it's life cycle, but not in short-years. (Get quotes, do the financial analysis.)

The intermittent flows from washers, etc are largely "unseen" by a the combi's controls, since the thermal mass of the tank buffers the small draw, and the controls onlymonitor & maintain the tank temp, and need not be concerned about the instantaneous flow (the way a tankless must).  If you need 20gpm of flow in short bursts, it doesn't really matter- the limiting factor for max flow will be your distribution plumbing and water pressure, not the burner or heat exchanger.  But the size of the burner needs to be comparable to the combined heat flows out of the tank for it to maintain temp over a substantial period of time (such as an endless teen shower. ;-) )