Please critique. Thanks.
The boiler is a mod-con, maybe a Munchkin T80, maybe something better. We only calculate about a 53000 Btu/h heat loss. Not shown, but it’ll be there, is a loop for the DHW.
One tstat for each of the radiant zones, one set high for the rad loop on the main floor. Outdoor reset for the mod-con.
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SamT
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Gene, I have built spec homes for almost 30 years now and as I understand it, this is a spec home.
I think you should just use a cheaper (and probably more reliable) boiler, because whoever you sell this house to most likely won't appreciate the fact that you did a lot of research and chose this boiler with their pocketbooks in mind.
They will look at one thing only...the price of your house, and you will most likely end up eating the cost of the frills you put in it.
The real value of your home will be its location and how it looks and fits the buyers life style. Anything beyond that is important to you but not to most buyers. I learned that lesson a long time ago.
Then how about something along the lines of a Laars 83% efficient LP-fired unit at 75K Btu/h output?
Or, let's go shopping and get real cheap, boiler wise. We would do oil but there is no room inside anywhere for a tank, and with an LP supply (we need LP anyway for the direct vent fireplace) we can get a supplier to give us an above ground tank as part of a supply contract. We'll simply assign the contract to the buyer at closing. We plan on finishing and being able to sell and close before the advent of next year's heating season.
And as for DHW, who cares how much it costs the buyers to use electricity at their high rates to heat it? An electric HWH is a whole lot cheaper that a tank with a bunch of copper lines to it and through it, plus the boiler and circulator run and controls to operate it.
You are absolutely right about the buyers having no clue at all about whether or not the heating plant is any good or not.
The only reason we're sticking PEX in the slab to heat the walkout lower level is because it seems more tedious to route radiator or baseboard supply and return in the slab than to run the PEX radiant runs. Our walls are ICF, and we don't want to hang overhead and then snake down the wall faces for the sheetrockers to shoot holes in the lines.
And the only reason we're going with rads upstairs instead of cheaper baseboards is because we've a large greatroom/kitchen/foyer area with so much heat loss (lotsa glass) and such little wall area for heat emitters, we've almost no choice but to use rads.
Certainly the piping loops and controls cannot get much cheaper, no?
Well...I like your heating system plan. There is certainly nothing wrong with that. I think you've come up with good solutions to the problems you face.
You are choosing a boiler based on fuel efficiency. This does not necessarily mean it is financially beneficial in the long run...in fact it probably isn't, considering the high initial cost, the additional maintenance, and the inevitable breakdowns you experience from a higher tech unit.
My wife's family owns the Weil Mclain distributorship for our area. I can only speak in terms of their boilers because other talk would be treason.
I have a 1987 boiler in my own home. It's got cast iron heat exchangers, induced draft, electric ignition etc. I pull the burners out every fall and give them a quick cleaning and button it up for the winter. I have not had one problem or spent one cent on that boiler in 20 years. It has an efficiency rating of about 84%.
The new units with cast iron heat exchangers are upper 80% efficient and the exchangers are guaranteed for life. The Ultra MC units cost about twice as much, have a heat exchanger life expectancy of 15 years, and may be 7 or 8 % more efficient if used in the proper setting.
My point is, I don't think you would necessarily be doing your potential buyer a big disservice by not installing an expensive high tech boiler.
When you are building spec homes, you must always build well, but don't go overboard on things you value, but the customer probably doesn't.
The number one rule of spec home building is: location, location, location and then visual appeal and lifestyle needs. Anything beyond that is coming off of your profit margin.
A takagi TK-Junior tankless runs $600 with direct vent kit, minus the stainless vent pipe and qualifies for a $300 tax credit. $300 unit is pretty hard to beat. It's all we used for years.
Beer was created so carpenters wouldn't rule the world.
Now you got it. You don't need the checks, but if they come with the pumps, great.
Personally, I would use grundfos 3 speed pumps.
I would think of putting some of your 'heating money' into really good insulation. I would also contact energy star to see what it would take to get the house rated as an energy star home. There are all sorts of rebate programs available. For instance in MA you can get up to $1500 back on an insul job from the state and I think a Fed tax refund of like 5% is additionally available.
http://www.energystar.gov/index.cfm?c=products.pr_tax_credits
I think with ICFs, he's probably most of the way there.
I am interested in Gene's decision here b/c I have a similar house, but with a very simple radiant system, just one zone per floor and a water heater - Is it worth the extra $$ to get a munchkin or similar mod/con boiler?
My experience has been that within an ICF shell, heat stays pretty well distributed no matter what you do - I haven't adjusted design temperatures based upon floor coverings etc.. (except adding staple up plates under the bathroom floors)
Let us know what you decide and why...
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Gene
Here's what I would do in your case.
This sketch does include a re-circulating hot water loop that you probably don't need and it eliminates all low voltage wiring. Of course you are free to substitute the $2,300 munchkin t-80 and a separate electric water heater for the $1,200 Rinnai and the $300 plate heat exchanger. But since the munchkin is 92% efficient as compared to the Rinnai at 86% and the Rinnai modulates from 15 to 199 kbtuh as compared to the munchkin's spread of 19 to 80 kbtuh I don't really see the value there. No offense please, I just think that if you have a tight enough place that you only need 53,000 BTU you really won't see the benefit of an additional 6% of efficiency.
Note that the temp in the slab is reduced by running a taco 006 circulating pump 24 hrs per day and only injecting hot water as demanded by the thermostat, we have used mixing valves there but over the years have discovered that they aren't really necessary so long as you keep the water coming out of the heat exchanger to 135 degrees or less. That may present a problem with your carpet upstairs in which case you would need to use a mixing valve at the slab and also on the hot water line going out to the house.
Since all the control wiring is line voltage we can use those $15 dollar 120 volt resistance heat T-stats from the box store. Also note that the big Taco 009 pump can be actuated by EITHER the t-stat in the tempering tank OR the flow switch on the heat exchanger loop as they are wired parallel. So it can come on to keep the tank at the temp you set OR it can come on to provide heat to the heat exchanger.
Of course there are fill valves and air bleeders and an expansion tank not drawn into this schematic but you'll hopefully get the gist of it. It's a rough and dirty system but I think it would solve your problem for the least cash with better durability.
Hey Gene, I came across your thread over at HeatingHelp.com while researching a dual boiler setup w/Tekmar controls that, as new member of the building committee at my church, I am trying to get a handle on.
Did you...or any of the other folks reading this thread..ever come up with or know a good explanation for the "closely spaced Tees" rule of thumb?
I'm having a heck of a time following the piping schematic for dual boiler systems (each boiler loop seems to be subject to the same closely spaced tee rule that heating zones are). I get that you don't want to pipe dual boilers in series, if the system really does operate part of the time on one boiler, because you would be wasting energy heating up the unfired boiler. But I can't picture in my mind the flows and pressures in the typical dual boiler pipe setup, and anyway it seems like both boilers and boiler circulating pumps are always on in the installation I'm looking at. So, short of the fact that two boilers provides built in redundancy, I don't see the reason for it.
Anyway, it's an interesting subject, given all the new control technology available...though something that fail-safes to a gravity feed situation might be a good thing in this day of overloaded power grids ;-)
The reason for close tees is to seperate the flow from one system to another.
Flow always goes from high pressure to low pressure.
If you measure the pressure on the outlet of each t, it will be the same.
(Good rule of thumb is no more than 4 pipe diameters apart)
Turn on a pump in the loop and the pressure changes, and you have flow.
If a boiler is not fireing,and there is flow through it, it is now a giant rad.
Not good. Costs money.
Are the pumps wired to the tekmar or to a starter?
I believe the pumps are controlled by a relay which in turn is operated by the Tekmar control.....I'm not sure what you mean by a "starter"as far as the closely spaced tees- (not meaning to be snotty here, just trying to get precise)I can see where if the tees are spaced far apart, you are likely to get more thermal siphoning than if they are close together.
But in a closed system, isn't the pressure pretty much same at any given height, and head pressure (as opposed to static pressure) dependent on velocity, not on distance from the pump?
A follow up...the control is a Tekmar 252.....not a current control, but not that old, either.
I just went and got the installation manual for a second reading, and I see where there is a single "system" pump control output. Since we have circulators on each of the boilers, plus at least three other zone circulating pumps, it isn't clear to me what signal is controlling which pump(s). It may be that the two boiler pumps are controlled together, but it seems like that would waste a lot of heat in situations where the heat load only requires one boiler firing.
Guess I'll have to look into it further...